objtool: Implement stack validation 2.0

This is a major rewrite of objtool. Instead of only tracking frame
pointer changes, it now tracks all stack-related operations, including
all register saves/restores.

In addition to making stack validation more robust, this also paves the
way for undwarf generation.

Signed-off-by: Josh Poimboeuf <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

tools/objtool/Documentation/stack-validation.txt

···
 
 c) Higher live patching compatibility rate
 
-   (NOTE: This is not yet implemented)
+   Livepatch has an optional "consistency model", which is needed for
+   more complex patches.  In order for the consistency model to work,
+   stack traces need to be reliable (or an unreliable condition needs to
+   be detectable).  Objtool makes that possible.
 
-   Currently with CONFIG_LIVEPATCH there's a basic live patching
-   framework which is safe for roughly 85-90% of "security" fixes.  But
-   patches can't have complex features like function dependency or
-   prototype changes, or data structure changes.
-
-   There's a strong need to support patches which have the more complex
-   features so that the patch compatibility rate for security fixes can
-   eventually approach something resembling 100%.  To achieve that, a
-   "consistency model" is needed, which allows tasks to be safely
-   transitioned from an unpatched state to a patched state.
-
-   One of the key requirements of the currently proposed livepatch
-   consistency model [*] is that it needs to walk the stack of each
-   sleeping task to determine if it can be transitioned to the patched
-   state.  If objtool can ensure that stack traces are reliable, this
-   consistency model can be used and the live patching compatibility
-   rate can be improved significantly.
-
-   [*] https://lkml.kernel.org/r/[e-mail]
-
+   For more details, see the livepatch documentation in the Linux kernel
+   source tree at Documentation/livepatch/livepatch.txt.
 
 Rules
 -----
···
    return normally.
 
 
-Errors in .S files
-------------------
+Objtool warnings
+----------------
 
-If you're getting an error in a compiled .S file which you don't
-understand, first make sure that the affected code follows the above
-rules.
+For asm files, if you're getting an error which doesn't make sense,
+first make sure that the affected code follows the above rules.
+
+For C files, the common culprits are inline asm statements and calls to
+"noreturn" functions.  See below for more details.
+
+Another possible cause for errors in C code is if the Makefile removes
+-fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
 
 Here are some examples of common warnings reported by objtool, what
 they mean, and suggestions for how to fix them.
 
 
-1. asm_file.o: warning: objtool: func()+0x128: call without frame pointer save/setup
+1. file.o: warning: objtool: func()+0x128: call without frame pointer save/setup
 
    The func() function made a function call without first saving and/or
-   updating the frame pointer.
+   updating the frame pointer, and CONFIG_FRAME_POINTER is enabled.
 
-   If func() is indeed a callable function, add proper frame pointer
-   logic using the FRAME_BEGIN and FRAME_END macros.  Otherwise, remove
-   its ELF function annotation by changing ENDPROC to END.
+   If the error is for an asm file, and func() is indeed a callable
+   function, add proper frame pointer logic using the FRAME_BEGIN and
+   FRAME_END macros.  Otherwise, if it's not a callable function, remove
+   its ELF function annotation by changing ENDPROC to END, and instead
+   use the manual CFI hint macros in asm/undwarf.h.
 
-   If you're getting this error in a .c file, see the "Errors in .c
-   files" section.
+   If it's a GCC-compiled .c file, the error may be because the function
+   uses an inline asm() statement which has a "call" instruction.  An
+   asm() statement with a call instruction must declare the use of the
+   stack pointer in its output operand.  For example, on x86_64:
 
+     register void *__sp asm("rsp");
+     asm volatile("call func" : "+r" (__sp));
 
-2. asm_file.o: warning: objtool: .text+0x53: return instruction outside of a callable function
-
-   A return instruction was detected, but objtool couldn't find a way
-   for a callable function to reach the instruction.
-
-   If the return instruction is inside (or reachable from) a callable
-   function, the function needs to be annotated with the ENTRY/ENDPROC
-   macros.
-
-   If you _really_ need a return instruction outside of a function, and
-   are 100% sure that it won't affect stack traces, you can tell
-   objtool to ignore it.  See the "Adding exceptions" section below.
+   Otherwise the stack frame may not get created before the call.
 
 
-3. asm_file.o: warning: objtool: func()+0x9: function has unreachable instruction
+2. file.o: warning: objtool: .text+0x53: unreachable instruction
 
-   The instruction lives inside of a callable function, but there's no
-   possible control flow path from the beginning of the function to the
-   instruction.
+   Objtool couldn't find a code path to reach the instruction.
 
-   If the instruction is actually needed, and it's actually in a
-   callable function, ensure that its function is properly annotated
-   with ENTRY/ENDPROC.
+   If the error is for an asm file, and the instruction is inside (or
+   reachable from) a callable function, the function should be annotated
+   with the ENTRY/ENDPROC macros (ENDPROC is the important one).
+   Otherwise, the code should probably be annotated with the CFI hint
+   macros in asm/undwarf.h so objtool and the unwinder can know the
+   stack state associated with the code.
+
+   If you're 100% sure the code won't affect stack traces, or if you're
+   a just a bad person, you can tell objtool to ignore it.  See the
+   "Adding exceptions" section below.
 
    If it's not actually in a callable function (e.g. kernel entry code),
    change ENDPROC to END.
 
 
-4. asm_file.o: warning: objtool: func(): can't find starting instruction
+4. file.o: warning: objtool: func(): can't find starting instruction
    or
-   asm_file.o: warning: objtool: func()+0x11dd: can't decode instruction
+   file.o: warning: objtool: func()+0x11dd: can't decode instruction
 
-   Did you put data in a text section?  If so, that can confuse
+   Does the file have data in a text section?  If so, that can confuse
    objtool's instruction decoder.  Move the data to a more appropriate
    section like .data or .rodata.
 
 
-5. asm_file.o: warning: objtool: func()+0x6: kernel entry/exit from callable instruction
+5. file.o: warning: objtool: func()+0x6: unsupported instruction in callable function
 
-   This is a kernel entry/exit instruction like sysenter or sysret.
-   Such instructions aren't allowed in a callable function, and are most
-   likely part of the kernel entry code.
+   This is a kernel entry/exit instruction like sysenter or iret.  Such
+   instructions aren't allowed in a callable function, and are most
+   likely part of the kernel entry code.  They should usually not have
+   the callable function annotation (ENDPROC) and should always be
+   annotated with the CFI hint macros in asm/undwarf.h.
 
-   If the instruction isn't actually in a callable function, change
-   ENDPROC to END.
 
+6. file.o: warning: objtool: func()+0x26: sibling call from callable instruction with modified stack frame
 
-6. asm_file.o: warning: objtool: func()+0x26: sibling call from callable instruction with changed frame pointer
-
-   This is a dynamic jump or a jump to an undefined symbol.  Stacktool
+   This is a dynamic jump or a jump to an undefined symbol.  Objtool
    assumed it's a sibling call and detected that the frame pointer
    wasn't first restored to its original state.
 
···
    destination code to the local file.
 
    If the instruction is not actually in a callable function (e.g.
-   kernel entry code), change ENDPROC to END.
+   kernel entry code), change ENDPROC to END and annotate manually with
+   the CFI hint macros in asm/undwarf.h.
 
 
-7. asm_file: warning: objtool: func()+0x5c: frame pointer state mismatch
+7. file: warning: objtool: func()+0x5c: stack state mismatch
 
    The instruction's frame pointer state is inconsistent, depending on
    which execution path was taken to reach the instruction.
 
-   Make sure the function pushes and sets up the frame pointer (for
-   x86_64, this means rbp) at the beginning of the function and pops it
-   at the end of the function.  Also make sure that no other code in the
-   function touches the frame pointer.
+   Make sure that, when CONFIG_FRAME_POINTER is enabled, the function
+   pushes and sets up the frame pointer (for x86_64, this means rbp) at
+   the beginning of the function and pops it at the end of the function.
+   Also make sure that no other code in the function touches the frame
+   pointer.
+
+   Another possibility is that the code has some asm or inline asm which
+   does some unusual things to the stack or the frame pointer.  In such
+   cases it's probably appropriate to use the CFI hint macros in
+   asm/undwarf.h.
 
 
-Errors in .c files
-------------------
-
-1. c_file.o: warning: objtool: funcA() falls through to next function funcB()
+8. file.o: warning: objtool: funcA() falls through to next function funcB()
 
    This means that funcA() doesn't end with a return instruction or an
    unconditional jump, and that objtool has determined that the function
···
       might be corrupt due to a gcc bug.  For more details, see:
       https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
 
-2. If you're getting any other objtool error in a compiled .c file, it
-   may be because the file uses an asm() statement which has a "call"
-   instruction.  An asm() statement with a call instruction must declare
-   the use of the stack pointer in its output operand.  For example, on
-   x86_64:
-
-     register void *__sp asm("rsp");
-     asm volatile("call func" : "+r" (__sp));
-
-   Otherwise the stack frame may not get created before the call.
-
-3. Another possible cause for errors in C code is if the Makefile removes
-   -fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options.
-
-Also see the above section for .S file errors for more information what
-the individual error messages mean.
 
 If the error doesn't seem to make sense, it could be a bug in objtool.
 Feel free to ask the objtool maintainer for help.

tools/objtool/Makefile

···
 all: $(OBJTOOL)
 
 INCLUDES := -I$(srctree)/tools/include -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi
-CFLAGS   += -Wall -Werror $(EXTRA_WARNINGS) -fomit-frame-pointer -O2 -g $(INCLUDES)
+CFLAGS   += -Wall -Werror $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -fomit-frame-pointer -O2 -g $(INCLUDES)
 LDFLAGS  += -lelf $(LIBSUBCMD)
 
 # Allow old libelf to be used:

tools/objtool/arch.h

···
 #define _ARCH_H
 
 #include <stdbool.h>
+#include <linux/list.h>
 #include "elf.h"
+#include "cfi.h"
 
-#define INSN_FP_SAVE		1
-#define INSN_FP_SETUP		2
-#define INSN_FP_RESTORE		3
-#define INSN_JUMP_CONDITIONAL	4
-#define INSN_JUMP_UNCONDITIONAL	5
-#define INSN_JUMP_DYNAMIC	6
-#define INSN_CALL		7
-#define INSN_CALL_DYNAMIC	8
-#define INSN_RETURN		9
-#define INSN_CONTEXT_SWITCH	10
-#define INSN_NOP		11
-#define INSN_OTHER		12
+#define INSN_JUMP_CONDITIONAL	1
+#define INSN_JUMP_UNCONDITIONAL	2
+#define INSN_JUMP_DYNAMIC	3
+#define INSN_CALL		4
+#define INSN_CALL_DYNAMIC	5
+#define INSN_RETURN		6
+#define INSN_CONTEXT_SWITCH	7
+#define INSN_STACK		8
+#define INSN_NOP		9
+#define INSN_OTHER		10
 #define INSN_LAST		INSN_OTHER
+
+enum op_dest_type {
+	OP_DEST_REG,
+	OP_DEST_REG_INDIRECT,
+	OP_DEST_MEM,
+	OP_DEST_PUSH,
+	OP_DEST_LEAVE,
+};
+
+struct op_dest {
+	enum op_dest_type type;
+	unsigned char reg;
+	int offset;
+};
+
+enum op_src_type {
+	OP_SRC_REG,
+	OP_SRC_REG_INDIRECT,
+	OP_SRC_CONST,
+	OP_SRC_POP,
+	OP_SRC_ADD,
+	OP_SRC_AND,
+};
+
+struct op_src {
+	enum op_src_type type;
+	unsigned char reg;
+	int offset;
+};
+
+struct stack_op {
+	struct op_dest dest;
+	struct op_src src;
+};
+
+void arch_initial_func_cfi_state(struct cfi_state *state);
 
 int arch_decode_instruction(struct elf *elf, struct section *sec,
 			    unsigned long offset, unsigned int maxlen,
 			    unsigned int *len, unsigned char *type,
-			    unsigned long *displacement);
+			    unsigned long *immediate, struct stack_op *op);
+
+bool arch_callee_saved_reg(unsigned char reg);
 
 #endif /* _ARCH_H */

tools/objtool/arch/x86/decode.c

···
 #include "../../arch.h"
 #include "../../warn.h"
 
+static unsigned char op_to_cfi_reg[][2] = {
+	{CFI_AX, CFI_R8},
+	{CFI_CX, CFI_R9},
+	{CFI_DX, CFI_R10},
+	{CFI_BX, CFI_R11},
+	{CFI_SP, CFI_R12},
+	{CFI_BP, CFI_R13},
+	{CFI_SI, CFI_R14},
+	{CFI_DI, CFI_R15},
+};
+
 static int is_x86_64(struct elf *elf)
 {
 	switch (elf->ehdr.e_machine) {
···
 	}
 }
 
+bool arch_callee_saved_reg(unsigned char reg)
+{
+	switch (reg) {
+	case CFI_BP:
+	case CFI_BX:
+	case CFI_R12:
+	case CFI_R13:
+	case CFI_R14:
+	case CFI_R15:
+		return true;
+
+	case CFI_AX:
+	case CFI_CX:
+	case CFI_DX:
+	case CFI_SI:
+	case CFI_DI:
+	case CFI_SP:
+	case CFI_R8:
+	case CFI_R9:
+	case CFI_R10:
+	case CFI_R11:
+	case CFI_RA:
+	default:
+		return false;
+	}
+}
+
 int arch_decode_instruction(struct elf *elf, struct section *sec,
 			    unsigned long offset, unsigned int maxlen,
 			    unsigned int *len, unsigned char *type,
-			    unsigned long *immediate)
+			    unsigned long *immediate, struct stack_op *op)
 {
 	struct insn insn;
-	int x86_64;
-	unsigned char op1, op2, ext;
+	int x86_64, sign;
+	unsigned char op1, op2, rex = 0, rex_b = 0, rex_r = 0, rex_w = 0,
+		      modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0,
+		      sib = 0;
 
 	x86_64 = is_x86_64(elf);
 	if (x86_64 == -1)
 		return -1;
 
-	insn_init(&insn, (void *)(sec->data + offset), maxlen, x86_64);
+	insn_init(&insn, sec->data->d_buf + offset, maxlen, x86_64);
 	insn_get_length(&insn);
-	insn_get_opcode(&insn);
-	insn_get_modrm(&insn);
-	insn_get_immediate(&insn);
 
 	if (!insn_complete(&insn)) {
 		WARN_FUNC("can't decode instruction", sec, offset);
···
 	op1 = insn.opcode.bytes[0];
 	op2 = insn.opcode.bytes[1];
 
+	if (insn.rex_prefix.nbytes) {
+		rex = insn.rex_prefix.bytes[0];
+		rex_w = X86_REX_W(rex) >> 3;
+		rex_r = X86_REX_R(rex) >> 2;
+		rex_b = X86_REX_B(rex);
+	}
+
+	if (insn.modrm.nbytes) {
+		modrm = insn.modrm.bytes[0];
+		modrm_mod = X86_MODRM_MOD(modrm);
+		modrm_reg = X86_MODRM_REG(modrm);
+		modrm_rm = X86_MODRM_RM(modrm);
+	}
+
+	if (insn.sib.nbytes)
+		sib = insn.sib.bytes[0];
+
 	switch (op1) {
-	case 0x55:
-		if (!insn.rex_prefix.nbytes)
-			/* push rbp */
-			*type = INSN_FP_SAVE;
+
+	case 0x1:
+	case 0x29:
+		if (rex_w && !rex_b && modrm_mod == 3 && modrm_rm == 4) {
+
+			/* add/sub reg, %rsp */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_ADD;
+			op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+			op->dest.type = OP_SRC_REG;
+			op->dest.reg = CFI_SP;
+		}
 		break;
 
-	case 0x5d:
-		if (!insn.rex_prefix.nbytes)
-			/* pop rbp */
-			*type = INSN_FP_RESTORE;
+	case 0x50 ... 0x57:
+
+		/* push reg */
+		*type = INSN_STACK;
+		op->src.type = OP_SRC_REG;
+		op->src.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
+		op->dest.type = OP_DEST_PUSH;
+
+		break;
+
+	case 0x58 ... 0x5f:
+
+		/* pop reg */
+		*type = INSN_STACK;
+		op->src.type = OP_SRC_POP;
+		op->dest.type = OP_DEST_REG;
+		op->dest.reg = op_to_cfi_reg[op1 & 0x7][rex_b];
+
+		break;
+
+	case 0x68:
+	case 0x6a:
+		/* push immediate */
+		*type = INSN_STACK;
+		op->src.type = OP_SRC_CONST;
+		op->dest.type = OP_DEST_PUSH;
 		break;
 
 	case 0x70 ... 0x7f:
 		*type = INSN_JUMP_CONDITIONAL;
 		break;
 
+	case 0x81:
+	case 0x83:
+		if (rex != 0x48)
+			break;
+
+		if (modrm == 0xe4) {
+			/* and imm, %rsp */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_AND;
+			op->src.reg = CFI_SP;
+			op->src.offset = insn.immediate.value;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = CFI_SP;
+			break;
+		}
+
+		if (modrm == 0xc4)
+			sign = 1;
+		else if (modrm == 0xec)
+			sign = -1;
+		else
+			break;
+
+		/* add/sub imm, %rsp */
+		*type = INSN_STACK;
+		op->src.type = OP_SRC_ADD;
+		op->src.reg = CFI_SP;
+		op->src.offset = insn.immediate.value * sign;
+		op->dest.type = OP_DEST_REG;
+		op->dest.reg = CFI_SP;
+		break;
+
 	case 0x89:
-		if (insn.rex_prefix.nbytes == 1 &&
-		    insn.rex_prefix.bytes[0] == 0x48 &&
-		    insn.modrm.nbytes && insn.modrm.bytes[0] == 0xe5)
-			/* mov rsp, rbp */
-			*type = INSN_FP_SETUP;
+		if (rex == 0x48 && modrm == 0xe5) {
+
+			/* mov %rsp, %rbp */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_REG;
+			op->src.reg = CFI_SP;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = CFI_BP;
+			break;
+		}
+		/* fallthrough */
+	case 0x88:
+		if (!rex_b &&
+		    (modrm_mod == 1 || modrm_mod == 2) && modrm_rm == 5) {
+
+			/* mov reg, disp(%rbp) */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_REG;
+			op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+			op->dest.type = OP_DEST_REG_INDIRECT;
+			op->dest.reg = CFI_BP;
+			op->dest.offset = insn.displacement.value;
+
+		} else if (rex_w && !rex_b && modrm_rm == 4 && sib == 0x24) {
+
+			/* mov reg, disp(%rsp) */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_REG;
+			op->src.reg = op_to_cfi_reg[modrm_reg][rex_r];
+			op->dest.type = OP_DEST_REG_INDIRECT;
+			op->dest.reg = CFI_SP;
+			op->dest.offset = insn.displacement.value;
+		}
+
+		break;
+
+	case 0x8b:
+		if (rex_w && !rex_b && modrm_mod == 1 && modrm_rm == 5) {
+
+			/* mov disp(%rbp), reg */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_REG_INDIRECT;
+			op->src.reg = CFI_BP;
+			op->src.offset = insn.displacement.value;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
+
+		} else if (rex_w && !rex_b && sib == 0x24 &&
+			   modrm_mod != 3 && modrm_rm == 4) {
+
+			/* mov disp(%rsp), reg */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_REG_INDIRECT;
+			op->src.reg = CFI_SP;
+			op->src.offset = insn.displacement.value;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];
+		}
+
 		break;
 
 	case 0x8d:
-		if (insn.rex_prefix.nbytes &&
-		    insn.rex_prefix.bytes[0] == 0x48 &&
-		    insn.modrm.nbytes && insn.modrm.bytes[0] == 0x2c &&
-		    insn.sib.nbytes && insn.sib.bytes[0] == 0x24)
-			/* lea %(rsp), %rbp */
-			*type = INSN_FP_SETUP;
+		if (rex == 0x48 && modrm == 0x65) {
+
+			/* lea -disp(%rbp), %rsp */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_ADD;
+			op->src.reg = CFI_BP;
+			op->src.offset = insn.displacement.value;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = CFI_SP;
+			break;
+		}
+
+		if (rex == 0x4c && modrm == 0x54 && sib == 0x24 &&
+		    insn.displacement.value == 8) {
+
+			/*
+			 * lea 0x8(%rsp), %r10
+			 *
+			 * Here r10 is the "drap" pointer, used as a stack
+			 * pointer helper when the stack gets realigned.
+			 */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_ADD;
+			op->src.reg = CFI_SP;
+			op->src.offset = 8;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = CFI_R10;
+			break;
+		}
+
+		if (rex == 0x4c && modrm == 0x6c && sib == 0x24 &&
+		    insn.displacement.value == 16) {
+
+			/*
+			 * lea 0x10(%rsp), %r13
+			 *
+			 * Here r13 is the "drap" pointer, used as a stack
+			 * pointer helper when the stack gets realigned.
+			 */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_ADD;
+			op->src.reg = CFI_SP;
+			op->src.offset = 16;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = CFI_R13;
+			break;
+		}
+
+		if (rex == 0x49 && modrm == 0x62 &&
+		    insn.displacement.value == -8) {
+
+			/*
+			 * lea -0x8(%r10), %rsp
+			 *
+			 * Restoring rsp back to its original value after a
+			 * stack realignment.
+			 */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_ADD;
+			op->src.reg = CFI_R10;
+			op->src.offset = -8;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = CFI_SP;
+			break;
+		}
+
+		if (rex == 0x49 && modrm == 0x65 &&
+		    insn.displacement.value == -16) {
+
+			/*
+			 * lea -0x10(%r13), %rsp
+			 *
+			 * Restoring rsp back to its original value after a
+			 * stack realignment.
+			 */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_ADD;
+			op->src.reg = CFI_R13;
+			op->src.offset = -16;
+			op->dest.type = OP_DEST_REG;
+			op->dest.reg = CFI_SP;
+			break;
+		}
+
+		break;
+
+	case 0x8f:
+		/* pop to mem */
+		*type = INSN_STACK;
+		op->src.type = OP_SRC_POP;
+		op->dest.type = OP_DEST_MEM;
 		break;
 
 	case 0x90:
 		*type = INSN_NOP;
 		break;
 
+	case 0x9c:
+		/* pushf */
+		*type = INSN_STACK;
+		op->src.type = OP_SRC_CONST;
+		op->dest.type = OP_DEST_PUSH;
+		break;
+
+	case 0x9d:
+		/* popf */
+		*type = INSN_STACK;
+		op->src.type = OP_SRC_POP;
+		op->dest.type = OP_DEST_MEM;
+		break;
+
 	case 0x0f:
+
 		if (op2 >= 0x80 && op2 <= 0x8f)
 			*type = INSN_JUMP_CONDITIONAL;
 		else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
 			 op2 == 0x35)
+
 			/* sysenter, sysret */
 			*type = INSN_CONTEXT_SWITCH;
+
 		else if (op2 == 0x0d || op2 == 0x1f)
+
 			/* nopl/nopw */
 			*type = INSN_NOP;
-		else if (op2 == 0x01 && insn.modrm.nbytes &&
-			 (insn.modrm.bytes[0] == 0xc2 ||
-			  insn.modrm.bytes[0] == 0xd8))
-			/* vmlaunch, vmrun */
-			*type = INSN_CONTEXT_SWITCH;
+
+		else if (op2 == 0xa0 || op2 == 0xa8) {
+
+			/* push fs/gs */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_CONST;
+			op->dest.type = OP_DEST_PUSH;
+
+		} else if (op2 == 0xa1 || op2 == 0xa9) {
+
+			/* pop fs/gs */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_POP;
+			op->dest.type = OP_DEST_MEM;
+		}
 
 		break;
 
-	case 0xc9: /* leave */
-		*type = INSN_FP_RESTORE;
+	case 0xc9:
+		/*
+		 * leave
+		 *
+		 * equivalent to:
+		 * mov bp, sp
+		 * pop bp
+		 */
+		*type = INSN_STACK;
+		op->dest.type = OP_DEST_LEAVE;
+
 		break;
 
-	case 0xe3: /* jecxz/jrcxz */
+	case 0xe3:
+		/* jecxz/jrcxz */
 		*type = INSN_JUMP_CONDITIONAL;
 		break;
 
···
 		break;
 
 	case 0xff:
-		ext = X86_MODRM_REG(insn.modrm.bytes[0]);
-		if (ext == 2 || ext == 3)
+		if (modrm_reg == 2 || modrm_reg == 3)
+
 			*type = INSN_CALL_DYNAMIC;
-		else if (ext == 4)
+
+		else if (modrm_reg == 4)
+
 			*type = INSN_JUMP_DYNAMIC;
-		else if (ext == 5) /*jmpf */
+
+		else if (modrm_reg == 5)
+
+			/* jmpf */
 			*type = INSN_CONTEXT_SWITCH;
+
+		else if (modrm_reg == 6) {
+
+			/* push from mem */
+			*type = INSN_STACK;
+			op->src.type = OP_SRC_CONST;
+			op->dest.type = OP_DEST_PUSH;
+		}
 
 		break;
 
···
 	*immediate = insn.immediate.nbytes ? insn.immediate.value : 0;
 
 	return 0;
+}
+
+void arch_initial_func_cfi_state(struct cfi_state *state)
+{
+	int i;
+
+	for (i = 0; i < CFI_NUM_REGS; i++) {
+		state->regs[i].base = CFI_UNDEFINED;
+		state->regs[i].offset = 0;
+	}
+
+	/* initial CFA (call frame address) */
+	state->cfa.base = CFI_SP;
+	state->cfa.offset = 8;
+
+	/* initial RA (return address) */
+	state->regs[16].base = CFI_CFA;
+	state->regs[16].offset = -8;
 }

tools/objtool/cfi.h

···
+/*
+ * Copyright (C) 2015-2017 Josh Poimboeuf <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _OBJTOOL_CFI_H
+#define _OBJTOOL_CFI_H
+
+#define CFI_UNDEFINED		-1
+#define CFI_CFA			-2
+#define CFI_SP_INDIRECT		-3
+#define CFI_BP_INDIRECT		-4
+
+#define CFI_AX			0
+#define CFI_DX			1
+#define CFI_CX			2
+#define CFI_BX			3
+#define CFI_SI			4
+#define CFI_DI			5
+#define CFI_BP			6
+#define CFI_SP			7
+#define CFI_R8			8
+#define CFI_R9			9
+#define CFI_R10			10
+#define CFI_R11			11
+#define CFI_R12			12
+#define CFI_R13			13
+#define CFI_R14			14
+#define CFI_R15			15
+#define CFI_RA			16
+#define CFI_NUM_REGS	17
+
+struct cfi_reg {
+	int base;
+	int offset;
+};
+
+struct cfi_state {
+	struct cfi_reg cfa;
+	struct cfi_reg regs[CFI_NUM_REGS];
+};
+
+#endif /* _OBJTOOL_CFI_H */

tools/objtool/check.c

···
 #include <linux/hashtable.h>
 #include <linux/kernel.h>
 
-#define STATE_FP_SAVED		0x1
-#define STATE_FP_SETUP		0x2
-#define STATE_FENTRY		0x4
-
 struct alternative {
 	struct list_head list;
 	struct instruction *insn;
···
 
 const char *objname;
 static bool nofp;
+struct cfi_state initial_func_cfi;
 
 static struct instruction *find_insn(struct objtool_file *file,
 				     struct section *sec, unsigned long offset)
···
 {
 	struct instruction *next = list_next_entry(insn, list);
 
-	if (&next->list == &file->insn_list || next->sec != insn->sec)
+	if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
 		return NULL;
 
 	return next;
···
 	struct section *sec;
 	struct symbol *sym;
 
-	list_for_each_entry(sec, &file->elf->sections, list)
+	for_each_sec(file, sec)
 		list_for_each_entry(sym, &sec->symbol_list, list)
 			if (!strncmp(sym->name, "__gcov_.", 8))
 				return true;
 
 	return false;
 }
-
-#define for_each_insn(file, insn)					\
-	list_for_each_entry(insn, &file->insn_list, list)
 
 #define func_for_each_insn(file, func, insn)				\
 	for (insn = find_insn(file, func->sec, func->offset);		\
···
 #define sec_for_each_insn_from(file, insn)				\
 	for (; insn; insn = next_insn_same_sec(file, insn))
 
+#define sec_for_each_insn_continue(file, insn)				\
+	for (insn = next_insn_same_sec(file, insn); insn;		\
+	     insn = next_insn_same_sec(file, insn))
 
 /*
  * Check if the function has been manually whitelisted with the
···
 static bool ignore_func(struct objtool_file *file, struct symbol *func)
 {
 	struct rela *rela;
-	struct instruction *insn;
 
 	/* check for STACK_FRAME_NON_STANDARD */
 	if (file->whitelist && file->whitelist->rela)
···
 			if (rela->sym->type == STT_FUNC && rela->sym == func)
 				return true;
 		}
-
-	/* check if it has a context switching instruction */
-	func_for_each_insn(file, func, insn)
-		if (insn->type == INSN_CONTEXT_SWITCH)
-			return true;
 
 	return false;
 }
···
 	return __dead_end_function(file, func, 0);
 }
 
+static void clear_insn_state(struct insn_state *state)
+{
+	int i;
+
+	memset(state, 0, sizeof(*state));
+	state->cfa.base = CFI_UNDEFINED;
+	for (i = 0; i < CFI_NUM_REGS; i++)
+		state->regs[i].base = CFI_UNDEFINED;
+	state->drap_reg = CFI_UNDEFINED;
+}
+
 /*
  * Call the arch-specific instruction decoder for all the instructions and add
  * them to the global instruction list.
···
 	struct instruction *insn;
 	int ret;
 
-	list_for_each_entry(sec, &file->elf->sections, list) {
+	for_each_sec(file, sec) {
 
 		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 			continue;
 
 		for (offset = 0; offset < sec->len; offset += insn->len) {
 			insn = malloc(sizeof(*insn));
+			if (!insn) {
+				WARN("malloc failed");
+				return -1;
+			}
 			memset(insn, 0, sizeof(*insn));
-
 			INIT_LIST_HEAD(&insn->alts);
+			clear_insn_state(&insn->state);
+
 			insn->sec = sec;
 			insn->offset = offset;
 
 			ret = arch_decode_instruction(file->elf, sec, offset,
 						      sec->len - offset,
 						      &insn->len, &insn->type,
-						      &insn->immediate);
+						      &insn->immediate,
+						      &insn->stack_op);
 			if (ret)
 				return ret;
 
···
 	struct section *sec;
 	struct symbol *func;
 
-	list_for_each_entry(sec, &file->elf->sections, list) {
+	for_each_sec(file, sec) {
 		list_for_each_entry(func, &sec->symbol_list, list) {
 			if (func->type != STT_FUNC)
 				continue;
···
 				continue;
 
 			func_for_each_insn(file, func, insn)
-				insn->visited = true;
+				insn->ignore = true;
 		}
 	}
 }
···
 		    insn->type != INSN_JUMP_UNCONDITIONAL)
 			continue;
 
-		/* skip ignores */
-		if (insn->visited)
+		if (insn->ignore)
 			continue;
 
 		rela = find_rela_by_dest_range(insn->sec, insn->offset,
···
 	}
 	memset(fake_jump, 0, sizeof(*fake_jump));
 	INIT_LIST_HEAD(&fake_jump->alts);
+	clear_insn_state(&fake_jump->state);
+
 	fake_jump->sec = special_alt->new_sec;
 	fake_jump->offset = -1;
 	fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 	fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
+	fake_jump->ignore = true;
 
 	if (!special_alt->new_len) {
 		*new_insn = fake_jump;
···
 	if (!file->rodata || !file->rodata->rela)
 		return 0;
 
-	list_for_each_entry(sec, &file->elf->sections, list) {
+	for_each_sec(file, sec) {
 		list_for_each_entry(func, &sec->symbol_list, list) {
 			if (func->type != STT_FUNC)
 				continue;
···
 	return false;
 }
 
-static bool has_modified_stack_frame(struct instruction *insn)
+static bool has_modified_stack_frame(struct insn_state *state)
 {
-	return (insn->state & STATE_FP_SAVED) ||
-	       (insn->state & STATE_FP_SETUP);
+	int i;
+
+	if (state->cfa.base != initial_func_cfi.cfa.base ||
+	    state->cfa.offset != initial_func_cfi.cfa.offset ||
+	    state->stack_size != initial_func_cfi.cfa.offset ||
+	    state->drap)
+		return true;
+
+	for (i = 0; i < CFI_NUM_REGS; i++)
+		if (state->regs[i].base != initial_func_cfi.regs[i].base ||
+		    state->regs[i].offset != initial_func_cfi.regs[i].offset)
+			return true;
+
+	return false;
 }
 
-static bool has_valid_stack_frame(struct instruction *insn)
+static bool has_valid_stack_frame(struct insn_state *state)
 {
-	return (insn->state & STATE_FP_SAVED) &&
-	       (insn->state & STATE_FP_SETUP);
+	if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
+	    state->regs[CFI_BP].offset == -16)
+		return true;
+
+	if (state->drap && state->regs[CFI_BP].base == CFI_BP)
+		return true;
+
+	return false;
 }
 
-static unsigned int frame_state(unsigned long state)
+static void save_reg(struct insn_state *state, unsigned char reg, int base,
+		     int offset)
 {
-	return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
+	if ((arch_callee_saved_reg(reg) ||
+	    (state->drap && reg == state->drap_reg)) &&
+	    state->regs[reg].base == CFI_UNDEFINED) {
+		state->regs[reg].base = base;
+		state->regs[reg].offset = offset;
+	}
+}
+
+static void restore_reg(struct insn_state *state, unsigned char reg)
+{
+	state->regs[reg].base = CFI_UNDEFINED;
+	state->regs[reg].offset = 0;
+}
+
+/*
+ * A note about DRAP stack alignment:
+ *
+ * GCC has the concept of a DRAP register, which is used to help keep track of
+ * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
+ * register.  The typical DRAP pattern is:
+ *
+ *   4c 8d 54 24 08		lea    0x8(%rsp),%r10
+ *   48 83 e4 c0		and    $0xffffffffffffffc0,%rsp
+ *   41 ff 72 f8		pushq  -0x8(%r10)
+ *   55				push   %rbp
+ *   48 89 e5			mov    %rsp,%rbp
+ *				(more pushes)
+ *   41 52			push   %r10
+ *				...
+ *   41 5a			pop    %r10
+ *				(more pops)
+ *   5d				pop    %rbp
+ *   49 8d 62 f8		lea    -0x8(%r10),%rsp
+ *   c3				retq
+ *
+ * There are some variations in the epilogues, like:
+ *
+ *   5b				pop    %rbx
+ *   41 5a			pop    %r10
+ *   41 5c			pop    %r12
+ *   41 5d			pop    %r13
+ *   41 5e			pop    %r14
+ *   c9				leaveq
+ *   49 8d 62 f8		lea    -0x8(%r10),%rsp
+ *   c3				retq
+ *
+ * and:
+ *
+ *   4c 8b 55 e8		mov    -0x18(%rbp),%r10
+ *   48 8b 5d e0		mov    -0x20(%rbp),%rbx
+ *   4c 8b 65 f0		mov    -0x10(%rbp),%r12
+ *   4c 8b 6d f8		mov    -0x8(%rbp),%r13
+ *   c9				leaveq
+ *   49 8d 62 f8		lea    -0x8(%r10),%rsp
+ *   c3				retq
+ *
+ * Sometimes r13 is used as the DRAP register, in which case it's saved and
+ * restored beforehand:
+ *
+ *   41 55			push   %r13
+ *   4c 8d 6c 24 10		lea    0x10(%rsp),%r13
+ *   48 83 e4 f0		and    $0xfffffffffffffff0,%rsp
+ *				...
+ *   49 8d 65 f0		lea    -0x10(%r13),%rsp
+ *   41 5d			pop    %r13
+ *   c3				retq
+ */
+static int update_insn_state(struct instruction *insn, struct insn_state *state)
+{
+	struct stack_op *op = &insn->stack_op;
+	struct cfi_reg *cfa = &state->cfa;
+	struct cfi_reg *regs = state->regs;
+
+	/* stack operations don't make sense with an undefined CFA */
+	if (cfa->base == CFI_UNDEFINED) {
+		if (insn->func) {
+			WARN_FUNC("undefined stack state", insn->sec, insn->offset);
+			return -1;
+		}
+		return 0;
+	}
+
+	switch (op->dest.type) {
+
+	case OP_DEST_REG:
+		switch (op->src.type) {
+
+		case OP_SRC_REG:
+			if (cfa->base == op->src.reg && cfa->base == CFI_SP &&
+			    op->dest.reg == CFI_BP && regs[CFI_BP].base == CFI_CFA &&
+			    regs[CFI_BP].offset == -cfa->offset) {
+
+				/* mov %rsp, %rbp */
+				cfa->base = op->dest.reg;
+				state->bp_scratch = false;
+			} else if (state->drap) {
+
+				/* drap: mov %rsp, %rbp */
+				regs[CFI_BP].base = CFI_BP;
+				regs[CFI_BP].offset = -state->stack_size;
+				state->bp_scratch = false;
+			} else if (!nofp) {
+
+				WARN_FUNC("unknown stack-related register move",
+					  insn->sec, insn->offset);
+				return -1;
+			}
+
+			break;
+
+		case OP_SRC_ADD:
+			if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
+
+				/* add imm, %rsp */
+				state->stack_size -= op->src.offset;
+				if (cfa->base == CFI_SP)
+					cfa->offset -= op->src.offset;
+				break;
+			}
+
+			if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
+
+				/* lea disp(%rbp), %rsp */
+				state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
+				break;
+			}
+
+			if (op->dest.reg != CFI_BP && op->src.reg == CFI_SP &&
+			    cfa->base == CFI_SP) {
+
+				/* drap: lea disp(%rsp), %drap */
+				state->drap_reg = op->dest.reg;
+				break;
+			}
+
+			if (state->drap && op->dest.reg == CFI_SP &&
+			    op->src.reg == state->drap_reg) {
+
+				 /* drap: lea disp(%drap), %rsp */
+				cfa->base = CFI_SP;
+				cfa->offset = state->stack_size = -op->src.offset;
+				state->drap_reg = CFI_UNDEFINED;
+				state->drap = false;
+				break;
+			}
+
+			if (op->dest.reg == state->cfa.base) {
+				WARN_FUNC("unsupported stack register modification",
+					  insn->sec, insn->offset);
+				return -1;
+			}
+
+			break;
+
+		case OP_SRC_AND:
+			if (op->dest.reg != CFI_SP ||
+			    (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
+			    (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
+				WARN_FUNC("unsupported stack pointer realignment",
+					  insn->sec, insn->offset);
+				return -1;
+			}
+
+			if (state->drap_reg != CFI_UNDEFINED) {
+				/* drap: and imm, %rsp */
+				cfa->base = state->drap_reg;
+				cfa->offset = state->stack_size = 0;
+				state->drap = true;
+
+			}
+
+			/*
+			 * Older versions of GCC (4.8ish) realign the stack
+			 * without DRAP, with a frame pointer.
+			 */
+
+			break;
+
+		case OP_SRC_POP:
+			if (!state->drap && op->dest.type == OP_DEST_REG &&
+			    op->dest.reg == cfa->base) {
+
+				/* pop %rbp */
+				cfa->base = CFI_SP;
+			}
+
+			if (regs[op->dest.reg].offset == -state->stack_size) {
+
+				if (state->drap && cfa->base == CFI_BP_INDIRECT &&
+				    op->dest.type == OP_DEST_REG &&
+				    op->dest.reg == state->drap_reg) {
+
+					/* drap: pop %drap */
+					cfa->base = state->drap_reg;
+					cfa->offset = 0;
+				}
+
+				restore_reg(state, op->dest.reg);
+			}
+
+			state->stack_size -= 8;
+			if (cfa->base == CFI_SP)
+				cfa->offset -= 8;
+
+			break;
+
+		case OP_SRC_REG_INDIRECT:
+			if (state->drap && op->src.reg == CFI_BP &&
+			    op->src.offset == regs[op->dest.reg].offset) {
+
+				/* drap: mov disp(%rbp), %reg */
+				if (op->dest.reg == state->drap_reg) {
+					cfa->base = state->drap_reg;
+					cfa->offset = 0;
+				}
+
+				restore_reg(state, op->dest.reg);
+
+			} else if (op->src.reg == cfa->base &&
+			    op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
+
+				/* mov disp(%rbp), %reg */
+				/* mov disp(%rsp), %reg */
+				restore_reg(state, op->dest.reg);
+			}
+
+			break;
+
+		default:
+			WARN_FUNC("unknown stack-related instruction",
+				  insn->sec, insn->offset);
+			return -1;
+		}
+
+		break;
+
+	case OP_DEST_PUSH:
+		state->stack_size += 8;
+		if (cfa->base == CFI_SP)
+			cfa->offset += 8;
+
+		if (op->src.type != OP_SRC_REG)
+			break;
+
+		if (state->drap) {
+			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
+
+				/* drap: push %drap */
+				cfa->base = CFI_BP_INDIRECT;
+				cfa->offset = -state->stack_size;
+
+				/* save drap so we know when to undefine it */
+				save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
+
+			} else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
+
+				/* drap: push %rbp */
+				state->stack_size = 0;
+
+			} else if (regs[op->src.reg].base == CFI_UNDEFINED) {
+
+				/* drap: push %reg */
+				save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
+			}
+
+		} else {
+
+			/* push %reg */
+			save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
+		}
+
+		/* detect when asm code uses rbp as a scratch register */
+		if (!nofp && insn->func && op->src.reg == CFI_BP &&
+		    cfa->base != CFI_BP)
+			state->bp_scratch = true;
+		break;
+
+	case OP_DEST_REG_INDIRECT:
+
+		if (state->drap) {
+			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
+
+				/* drap: mov %drap, disp(%rbp) */
+				cfa->base = CFI_BP_INDIRECT;
+				cfa->offset = op->dest.offset;
+
+				/* save drap so we know when to undefine it */
+				save_reg(state, op->src.reg, CFI_CFA, op->dest.offset);
+			}
+
+			else if (regs[op->src.reg].base == CFI_UNDEFINED) {
+
+				/* drap: mov reg, disp(%rbp) */
+				save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
+			}
+
+		} else if (op->dest.reg == cfa->base) {
+
+			/* mov reg, disp(%rbp) */
+			/* mov reg, disp(%rsp) */
+			save_reg(state, op->src.reg, CFI_CFA,
+				 op->dest.offset - state->cfa.offset);
+		}
+
+		break;
+
+	case OP_DEST_LEAVE:
+		if ((!state->drap && cfa->base != CFI_BP) ||
+		    (state->drap && cfa->base != state->drap_reg)) {
+			WARN_FUNC("leave instruction with modified stack frame",
+				  insn->sec, insn->offset);
+			return -1;
+		}
+
+		/* leave (mov %rbp, %rsp; pop %rbp) */
+
+		state->stack_size = -state->regs[CFI_BP].offset - 8;
+		restore_reg(state, CFI_BP);
+
+		if (!state->drap) {
+			cfa->base = CFI_SP;
+			cfa->offset -= 8;
+		}
+
+		break;
+
+	case OP_DEST_MEM:
+		if (op->src.type != OP_SRC_POP) {
+			WARN_FUNC("unknown stack-related memory operation",
+				  insn->sec, insn->offset);
+			return -1;
+		}
+
+		/* pop mem */
+		state->stack_size -= 8;
+		if (cfa->base == CFI_SP)
+			cfa->offset -= 8;
+
+		break;
+
+	default:
+		WARN_FUNC("unknown stack-related instruction",
+			  insn->sec, insn->offset);
+		return -1;
+	}
+
+	return 0;
+}
+
+static bool insn_state_match(struct instruction *insn, struct insn_state *state)
+{
+	struct insn_state *state1 = &insn->state, *state2 = state;
+	int i;
+
+	if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
+		WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
+			  insn->sec, insn->offset,
+			  state1->cfa.base, state1->cfa.offset,
+			  state2->cfa.base, state2->cfa.offset);
+
+	} else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
+		for (i = 0; i < CFI_NUM_REGS; i++) {
+			if (!memcmp(&state1->regs[i], &state2->regs[i],
+				    sizeof(struct cfi_reg)))
+				continue;
+
+			WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
+				  insn->sec, insn->offset,
+				  i, state1->regs[i].base, state1->regs[i].offset,
+				  i, state2->regs[i].base, state2->regs[i].offset);
+			break;
+		}
+
+	} else if (state1->drap != state2->drap ||
+		 (state1->drap && state1->drap_reg != state2->drap_reg)) {
+		WARN_FUNC("stack state mismatch: drap1=%d(%d) drap2=%d(%d)",
+			  insn->sec, insn->offset,
+			  state1->drap, state1->drap_reg,
+			  state2->drap, state2->drap_reg);
+
+	} else
+		return true;
+
+	return false;
 }
 
 /*
···
  * each instruction and validate all the rules described in
  * tools/objtool/Documentation/stack-validation.txt.
  */
-static int validate_branch(struct objtool_file *file,
-			   struct instruction *first, unsigned char first_state)
+static int validate_branch(struct objtool_file *file, struct instruction *first,
+			   struct insn_state state)
 {
 	struct alternative *alt;
 	struct instruction *insn;
 	struct section *sec;
 	struct symbol *func = NULL;
-	unsigned char state;
 	int ret;
 
 	insn = first;
 	sec = insn->sec;
-	state = first_state;
 
 	if (insn->alt_group && list_empty(&insn->alts)) {
 		WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
 			  sec, insn->offset);
-		return 1;
+		return -1;
 	}
 
 	while (1) {
···
 				     func->name, insn->func->name);
 				return 1;
 			}
-
-			func = insn->func;
 		}
 
+		func = insn->func;
+
 		if (insn->visited) {
-			if (frame_state(insn->state) != frame_state(state)) {
-				WARN_FUNC("frame pointer state mismatch",
-					  sec, insn->offset);
+			if (!!insn_state_match(insn, &state))
 				return 1;
-			}
 
 			return 0;
 		}
 
-		insn->visited = true;
 		insn->state = state;
+
+		insn->visited = true;
 
 		list_for_each_entry(alt, &insn->alts, list) {
 			ret = validate_branch(file, alt->insn, state);
···
 
 		switch (insn->type) {
 
-		case INSN_FP_SAVE:
-			if (!nofp) {
-				if (state & STATE_FP_SAVED) {
-					WARN_FUNC("duplicate frame pointer save",
-						  sec, insn->offset);
-					return 1;
-				}
-				state |= STATE_FP_SAVED;
-			}
-			break;
-
-		case INSN_FP_SETUP:
-			if (!nofp) {
-				if (state & STATE_FP_SETUP) {
-					WARN_FUNC("duplicate frame pointer setup",
-						  sec, insn->offset);
-					return 1;
-				}
-				state |= STATE_FP_SETUP;
-			}
-			break;
-
-		case INSN_FP_RESTORE:
-			if (!nofp) {
-				if (has_valid_stack_frame(insn))
-					state &= ~STATE_FP_SETUP;
-
-				state &= ~STATE_FP_SAVED;
-			}
-			break;
-
 		case INSN_RETURN:
-			if (!nofp && has_modified_stack_frame(insn)) {
-				WARN_FUNC("return without frame pointer restore",
+			if (func && has_modified_stack_frame(&state)) {
+				WARN_FUNC("return with modified stack frame",
 					  sec, insn->offset);
 				return 1;
 			}
+
+			if (state.bp_scratch) {
+				WARN("%s uses BP as a scratch register",
+				     insn->func->name);
+				return 1;
+			}
+
 			return 0;
 
 		case INSN_CALL:
-			if (is_fentry_call(insn)) {
-				state |= STATE_FENTRY;
+			if (is_fentry_call(insn))
 				break;
-			}
 
 			ret = dead_end_function(file, insn->call_dest);
 			if (ret == 1)
···
 
 			/* fallthrough */
 		case INSN_CALL_DYNAMIC:
-			if (!nofp && !has_valid_stack_frame(insn)) {
+			if (!nofp && func && !has_valid_stack_frame(&state)) {
 				WARN_FUNC("call without frame pointer save/setup",
 					  sec, insn->offset);
 				return 1;
···
 						      state);
 				if (ret)
 					return 1;
-			} else if (has_modified_stack_frame(insn)) {
-				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
+			} else if (func && has_modified_stack_frame(&state)) {
+				WARN_FUNC("sibling call from callable instruction with modified stack frame",
 					  sec, insn->offset);
 				return 1;
 			} /* else it's a sibling call */
···
 			break;
 
 		case INSN_JUMP_DYNAMIC:
-			if (list_empty(&insn->alts) &&
-			    has_modified_stack_frame(insn)) {
-				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
+			if (func && list_empty(&insn->alts) &&
+			    has_modified_stack_frame(&state)) {
+				WARN_FUNC("sibling call from callable instruction with modified stack frame",
 					  sec, insn->offset);
 				return 1;
 			}
 
 			return 0;
+
+		case INSN_CONTEXT_SWITCH:
+			if (func) {
+				WARN_FUNC("unsupported instruction in callable function",
+					  sec, insn->offset);
+				return 1;
+			}
+			return 0;
+
+		case INSN_STACK:
+			if (update_insn_state(insn, &state))
+				return -1;
+
+			break;
 
 		default:
 			break;
···
 			"__ubsan_handle_builtin_unreachable"));
 }
 
-static bool ignore_unreachable_insn(struct symbol *func,
-				    struct instruction *insn)
+static bool ignore_unreachable_insn(struct instruction *insn)
 {
 	int i;
 
-	if (insn->type == INSN_NOP)
+	if (insn->ignore || insn->type == INSN_NOP)
+		return true;
+
+	/*
+	 * Ignore any unused exceptions.  This can happen when a whitelisted
+	 * function has an exception table entry.
+	 */
+	if (!strcmp(insn->sec->name, ".fixup"))
 		return true;
 
 	/*
···
 	 *
 	 * End the search at 5 instructions to avoid going into the weeds.
 	 */
+	if (!insn->func)
+		return false;
 	for (i = 0; i < 5; i++) {
 
 		if (is_kasan_insn(insn) || is_ubsan_insn(insn))
···
 			continue;
 		}
 
-		if (insn->offset + insn->len >= func->offset + func->len)
+		if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
 			break;
 		insn = list_next_entry(insn, list);
 	}
···
 	struct section *sec;
 	struct symbol *func;
 	struct instruction *insn;
+	struct insn_state state;
 	int ret, warnings = 0;
 
-	list_for_each_entry(sec, &file->elf->sections, list) {
+	clear_insn_state(&state);
+
+	state.cfa = initial_func_cfi.cfa;
+	memcpy(&state.regs, &initial_func_cfi.regs,
+	       CFI_NUM_REGS * sizeof(struct cfi_reg));
+	state.stack_size = initial_func_cfi.cfa.offset;
+
+	for_each_sec(file, sec) {
 		list_for_each_entry(func, &sec->symbol_list, list) {
 			if (func->type != STT_FUNC)
 				continue;
 
 			insn = find_insn(file, sec, func->offset);
-			if (!insn)
+			if (!insn || insn->ignore)
 				continue;
 
-			ret = validate_branch(file, insn, 0);
+			ret = validate_branch(file, insn, state);
 			warnings += ret;
-		}
-	}
-
-	list_for_each_entry(sec, &file->elf->sections, list) {
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
-				continue;
-
-			func_for_each_insn(file, func, insn) {
-				if (insn->visited)
-					continue;
-
-				insn->visited = true;
-
-				if (file->ignore_unreachables || warnings ||
-				    ignore_unreachable_insn(func, insn))
-					continue;
-
-				/*
-				 * gcov produces a lot of unreachable
-				 * instructions.  If we get an unreachable
-				 * warning and the file has gcov enabled, just
-				 * ignore it, and all other such warnings for
-				 * the file.
-				 */
-				if (!file->ignore_unreachables &&
-				    gcov_enabled(file)) {
-					file->ignore_unreachables = true;
-					continue;
-				}
-
-				WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
-				warnings++;
-			}
 		}
 	}
 
 	return warnings;
 }
 
-static int validate_uncallable_instructions(struct objtool_file *file)
+static int validate_reachable_instructions(struct objtool_file *file)
 {
 	struct instruction *insn;
-	int warnings = 0;
+
+	if (file->ignore_unreachables)
+		return 0;
 
 	for_each_insn(file, insn) {
-		if (!insn->visited && insn->type == INSN_RETURN) {
-			WARN_FUNC("return instruction outside of a callable function",
-				  insn->sec, insn->offset);
-			warnings++;
-		}
+		if (insn->visited || ignore_unreachable_insn(insn))
+			continue;
+
+		/*
+		 * gcov produces a lot of unreachable instructions.  If we get
+		 * an unreachable warning and the file has gcov enabled, just
+		 * ignore it, and all other such warnings for the file.  Do
+		 * this here because this is an expensive function.
+		 */
+		if (gcov_enabled(file))
+			return 0;
+
+		WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
+		return 1;
 	}
 
-	return warnings;
+	return 0;
 }
 
 static void cleanup(struct objtool_file *file)
···
 	nofp = _nofp;
 
 	file.elf = elf_open(objname);
-	if (!file.elf) {
-		fprintf(stderr, "error reading elf file %s\n", objname);
+	if (!file.elf)
 		return 1;
-	}
 
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
···
 	file.ignore_unreachables = false;
 	file.c_file = find_section_by_name(file.elf, ".comment");
 
+	arch_initial_func_cfi_state(&initial_func_cfi);
+
 	ret = decode_sections(&file);
 	if (ret < 0)
 		goto out;
 	warnings += ret;
+
+	if (list_empty(&file.insn_list))
+		goto out;
 
 	ret = validate_functions(&file);
 	if (ret < 0)
 		goto out;
 	warnings += ret;
 
-	ret = validate_uncallable_instructions(&file);
-	if (ret < 0)
-		goto out;
-	warnings += ret;
+	if (!warnings) {
+		ret = validate_reachable_instructions(&file);
+		if (ret < 0)
+			goto out;
+		warnings += ret;
+	}
 
 out:
 	cleanup(&file);

tools/objtool/check.h

···
 
 #include <stdbool.h>
 #include "elf.h"
+#include "cfi.h"
 #include "arch.h"
 #include <linux/hashtable.h>
+
+struct insn_state {
+	struct cfi_reg cfa;
+	struct cfi_reg regs[CFI_NUM_REGS];
+	int stack_size;
+	bool bp_scratch;
+	bool drap;
+	int drap_reg;
+};
 
 struct instruction {
 	struct list_head list;
 	struct hlist_node hash;
 	struct section *sec;
 	unsigned long offset;
-	unsigned int len, state;
+	unsigned int len;
 	unsigned char type;
 	unsigned long immediate;
-	bool alt_group, visited, dead_end;
+	bool alt_group, visited, dead_end, ignore;
 	struct symbol *call_dest;
 	struct instruction *jump_dest;
 	struct list_head alts;
 	struct symbol *func;
+	struct stack_op stack_op;
+	struct insn_state state;
 };
 
 struct objtool_file {
···
 };
 
 int check(const char *objname, bool nofp);
+
+#define for_each_insn(file, insn)					\
+	list_for_each_entry(insn, &file->insn_list, list)
 
 #endif /* _CHECK_H */

tools/objtool/elf.c

···
 #define ELF_C_READ_MMAP ELF_C_READ
 #endif
 
+#define WARN_ELF(format, ...)					\
+	WARN(format ": %s", ##__VA_ARGS__, elf_errmsg(-1))
+
 struct section *find_section_by_name(struct elf *elf, const char *name)
 {
 	struct section *sec;
···
 	int i;
 
 	if (elf_getshdrnum(elf->elf, &sections_nr)) {
-		perror("elf_getshdrnum");
+		WARN_ELF("elf_getshdrnum");
 		return -1;
 	}
 
 	if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
-		perror("elf_getshdrstrndx");
+		WARN_ELF("elf_getshdrstrndx");
 		return -1;
 	}
 
···
 
 		s = elf_getscn(elf->elf, i);
 		if (!s) {
-			perror("elf_getscn");
+			WARN_ELF("elf_getscn");
 			return -1;
 		}
 
 		sec->idx = elf_ndxscn(s);
 
 		if (!gelf_getshdr(s, &sec->sh)) {
-			perror("gelf_getshdr");
+			WARN_ELF("gelf_getshdr");
 			return -1;
 		}
 
 		sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 		if (!sec->name) {
-			perror("elf_strptr");
+			WARN_ELF("elf_strptr");
 			return -1;
 		}
 
-		sec->elf_data = elf_getdata(s, NULL);
-		if (!sec->elf_data) {
-			perror("elf_getdata");
+		sec->data = elf_getdata(s, NULL);
+		if (!sec->data) {
+			WARN_ELF("elf_getdata");
 			return -1;
 		}
 
-		if (sec->elf_data->d_off != 0 ||
-		    sec->elf_data->d_size != sec->sh.sh_size) {
+		if (sec->data->d_off != 0 ||
+		    sec->data->d_size != sec->sh.sh_size) {
 			WARN("unexpected data attributes for %s", sec->name);
 			return -1;
 		}
 
-		sec->data = (unsigned long)sec->elf_data->d_buf;
-		sec->len = sec->elf_data->d_size;
+		sec->len = sec->data->d_size;
 	}
 
 	/* sanity check, one more call to elf_nextscn() should return NULL */
···
 
 		sym->idx = i;
 
-		if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) {
-			perror("gelf_getsym");
+		if (!gelf_getsym(symtab->data, i, &sym->sym)) {
+			WARN_ELF("gelf_getsym");
 			goto err;
 		}
 
 		sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 				       sym->sym.st_name);
 		if (!sym->name) {
-			perror("elf_strptr");
+			WARN_ELF("elf_strptr");
 			goto err;
 		}
 
···
 			}
 			memset(rela, 0, sizeof(*rela));
 
-			if (!gelf_getrela(sec->elf_data, i, &rela->rela)) {
-				perror("gelf_getrela");
+			if (!gelf_getrela(sec->data, i, &rela->rela)) {
+				WARN_ELF("gelf_getrela");
 				return -1;
 			}
 
···
 
 	INIT_LIST_HEAD(&elf->sections);
 
-	elf->name = strdup(name);
-	if (!elf->name) {
-		perror("strdup");
-		goto err;
-	}
-
 	elf->fd = open(name, O_RDONLY);
 	if (elf->fd == -1) {
 		perror("open");
···
 
 	elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL);
 	if (!elf->elf) {
-		perror("elf_begin");
+		WARN_ELF("elf_begin");
 		goto err;
 	}
 
 	if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
-		perror("gelf_getehdr");
+		WARN_ELF("gelf_getehdr");
 		goto err;
 	}
 
···
 	struct symbol *sym, *tmpsym;
 	struct rela *rela, *tmprela;
 
+	if (elf->elf)
+		elf_end(elf->elf);
+
+	if (elf->fd > 0)
+		close(elf->fd);
+
 	list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 		list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 			list_del(&sym->list);
···
 		list_del(&sec->list);
 		free(sec);
 	}
-	if (elf->name)
-		free(elf->name);
-	if (elf->fd > 0)
-		close(elf->fd);
-	if (elf->elf)
-		elf_end(elf->elf);
+
 	free(elf);
 }

tools/objtool/elf.h

···
 	DECLARE_HASHTABLE(rela_hash, 16);
 	struct section *base, *rela;
 	struct symbol *sym;
-	Elf_Data *elf_data;
+	Elf_Data *data;
 	char *name;
 	int idx;
-	unsigned long data;
 	unsigned int len;
 };
 
···
 struct symbol *find_containing_func(struct section *sec, unsigned long offset);
 void elf_close(struct elf *elf);
 
-
+#define for_each_sec(file, sec)						\
+	list_for_each_entry(sec, &file->elf->sections, list)
 
 #endif /* _OBJTOOL_ELF_H */

tools/objtool/special.c

···
 	alt->jump_or_nop = entry->jump_or_nop;
 
 	if (alt->group) {
-		alt->orig_len = *(unsigned char *)(sec->data + offset +
+		alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset +
 						   entry->orig_len);
-		alt->new_len = *(unsigned char *)(sec->data + offset +
+		alt->new_len = *(unsigned char *)(sec->data->d_buf + offset +
 						  entry->new_len);
 	}
 
 	if (entry->feature) {
 		unsigned short feature;
 
-		feature = *(unsigned short *)(sec->data + offset +
+		feature = *(unsigned short *)(sec->data->d_buf + offset +
 					      entry->feature);
 
 		/*

tools/objtool/warn.h

···
 #ifndef _WARN_H
 #define _WARN_H
 
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include "elf.h"
+
 extern const char *objname;
 
 static inline char *offstr(struct section *sec, unsigned long offset)
···
 	WARN("%s: " format, _str, ##__VA_ARGS__);	\
 	free(_str);					\
 })
+
+#define WARN_ELF(format, ...)				\
+	WARN(format ": %s", ##__VA_ARGS__, elf_errmsg(-1))
 
 #endif /* _WARN_H */