MIPS: Move signal trampolines off of the stack.

This is a follow on to the vdso patch.

Since all processes now have signal trampolines permanently mapped, we
can use those instead of putting the trampoline on the stack and
invalidating the corresponding icache across all CPUs. We also get rid
of a bunch of ICACHE_REFILLS_WORKAROUND_WAR code.

[Ralf: GDB 7.1 which has the necessary modifications to allow backtracing
over signal frames will supposedly be released tomorrow. The old signal
frame format obsoleted by this patch exists in two variations, for sane
processors and for those requiring ICACHE_REFILLS_WORKAROUND_WAR. So
there was never a GDB which did support backtracing over signal frames
on all MIPS systems. This convinved me this series should be applied and
pushed upstream as soon as possible.]

Signed-off-by: David Daney <[e-mail]>
To: [e-mail]
Patchwork: http://patchwork.linux-mips.org/patch/974/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/include/asm/abi.h

···
 #include <asm/siginfo.h>
 
 struct mips_abi {
-	int (* const setup_frame)(struct k_sigaction * ka,
+	int (* const setup_frame)(void *sig_return, struct k_sigaction *ka,
 	                          struct pt_regs *regs, int signr,
 	                          sigset_t *set);
-	int (* const setup_rt_frame)(struct k_sigaction * ka,
+	const unsigned long	signal_return_offset;
+	int (* const setup_rt_frame)(void *sig_return, struct k_sigaction *ka,
 	                       struct pt_regs *regs, int signr,
 	                       sigset_t *set, siginfo_t *info);
+	const unsigned long	rt_signal_return_offset;
 	const unsigned long	restart;
 };
 

arch/mips/kernel/signal-common.h

···
  */
 extern void __user *get_sigframe(struct k_sigaction *ka, struct pt_regs *regs,
 				 size_t frame_size);
-/*
- * install trampoline code to get back from the sig handler
- */
-extern int install_sigtramp(unsigned int __user *tramp, unsigned int syscall);
-
 /* Check and clear pending FPU exceptions in saved CSR */
 extern int fpcsr_pending(unsigned int __user *fpcsr);
 

arch/mips/kernel/signal.c

···
 #include <asm/ucontext.h>
 #include <asm/cpu-features.h>
 #include <asm/war.h>
+#include <asm/vdso.h>
 
 #include "signal-common.h"
 
···
 extern asmlinkage int fpu_emulator_save_context(struct sigcontext __user *sc);
 extern asmlinkage int fpu_emulator_restore_context(struct sigcontext __user *sc);
 
-/*
- * Horribly complicated - with the bloody RM9000 workarounds enabled
- * the signal trampolines is moving to the end of the structure so we can
- * increase the alignment without breaking software compatibility.
- */
-#if ICACHE_REFILLS_WORKAROUND_WAR == 0
-
 struct sigframe {
 	u32 sf_ass[4];		/* argument save space for o32 */
-	u32 sf_code[2];		/* signal trampoline */
+	u32 sf_pad[2];		/* Was: signal trampoline */
 	struct sigcontext sf_sc;
 	sigset_t sf_mask;
 };
 
 struct rt_sigframe {
 	u32 rs_ass[4];		/* argument save space for o32 */
-	u32 rs_code[2];		/* signal trampoline */
+	u32 rs_pad[2];		/* Was: signal trampoline */
 	struct siginfo rs_info;
 	struct ucontext rs_uc;
 };
-
-#else
-
-struct sigframe {
-	u32 sf_ass[4];			/* argument save space for o32 */
-	u32 sf_pad[2];
-	struct sigcontext sf_sc;	/* hw context */
-	sigset_t sf_mask;
-	u32 sf_code[8] ____cacheline_aligned;	/* signal trampoline */
-};
-
-struct rt_sigframe {
-	u32 rs_ass[4];			/* argument save space for o32 */
-	u32 rs_pad[2];
-	struct siginfo rs_info;
-	struct ucontext rs_uc;
-	u32 rs_code[8] ____cacheline_aligned;	/* signal trampoline */
-};
-
-#endif
 
 /*
  * Helper routines
···
 		sp = current->sas_ss_sp + current->sas_ss_size;
 
 	return (void __user *)((sp - frame_size) & (ICACHE_REFILLS_WORKAROUND_WAR ? ~(cpu_icache_line_size()-1) : ALMASK));
-}
-
-int install_sigtramp(unsigned int __user *tramp, unsigned int syscall)
-{
-	int err;
-
-	/*
-	 * Set up the return code ...
-	 *
-	 *         li      v0, __NR__foo_sigreturn
-	 *         syscall
-	 */
-
-	err = __put_user(0x24020000 + syscall, tramp + 0);
-	err |= __put_user(0x0000000c         , tramp + 1);
-	if (ICACHE_REFILLS_WORKAROUND_WAR) {
-		err |= __put_user(0, tramp + 2);
-		err |= __put_user(0, tramp + 3);
-		err |= __put_user(0, tramp + 4);
-		err |= __put_user(0, tramp + 5);
-		err |= __put_user(0, tramp + 6);
-		err |= __put_user(0, tramp + 7);
-	}
-	flush_cache_sigtramp((unsigned long) tramp);
-
-	return err;
 }
 
 /*
···
 }
 
 #ifdef CONFIG_TRAD_SIGNALS
-static int setup_frame(struct k_sigaction * ka, struct pt_regs *regs,
-	int signr, sigset_t *set)
+static int setup_frame(void *sig_return, struct k_sigaction *ka,
+		       struct pt_regs *regs, int signr, sigset_t *set)
 {
 	struct sigframe __user *frame;
 	int err = 0;
···
 	frame = get_sigframe(ka, regs, sizeof(*frame));
 	if (!access_ok(VERIFY_WRITE, frame, sizeof (*frame)))
 		goto give_sigsegv;
-
-	err |= install_sigtramp(frame->sf_code, __NR_sigreturn);
 
 	err |= setup_sigcontext(regs, &frame->sf_sc);
 	err |= __copy_to_user(&frame->sf_mask, set, sizeof(*set));
···
 	regs->regs[ 5] = 0;
 	regs->regs[ 6] = (unsigned long) &frame->sf_sc;
 	regs->regs[29] = (unsigned long) frame;
-	regs->regs[31] = (unsigned long) frame->sf_code;
+	regs->regs[31] = (unsigned long) sig_return;
 	regs->cp0_epc = regs->regs[25] = (unsigned long) ka->sa.sa_handler;
 
 	DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
···
 }
 #endif
 
-static int setup_rt_frame(struct k_sigaction * ka, struct pt_regs *regs,
-	int signr, sigset_t *set, siginfo_t *info)
+static int setup_rt_frame(void *sig_return, struct k_sigaction *ka,
+			  struct pt_regs *regs,	int signr, sigset_t *set,
+			  siginfo_t *info)
 {
 	struct rt_sigframe __user *frame;
 	int err = 0;
···
 	frame = get_sigframe(ka, regs, sizeof(*frame));
 	if (!access_ok(VERIFY_WRITE, frame, sizeof (*frame)))
 		goto give_sigsegv;
-
-	err |= install_sigtramp(frame->rs_code, __NR_rt_sigreturn);
 
 	/* Create siginfo.  */
 	err |= copy_siginfo_to_user(&frame->rs_info, info);
···
 	regs->regs[ 5] = (unsigned long) &frame->rs_info;
 	regs->regs[ 6] = (unsigned long) &frame->rs_uc;
 	regs->regs[29] = (unsigned long) frame;
-	regs->regs[31] = (unsigned long) frame->rs_code;
+	regs->regs[31] = (unsigned long) sig_return;
 	regs->cp0_epc = regs->regs[25] = (unsigned long) ka->sa.sa_handler;
 
 	DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
···
 struct mips_abi mips_abi = {
 #ifdef CONFIG_TRAD_SIGNALS
 	.setup_frame	= setup_frame,
+	.signal_return_offset = offsetof(struct mips_vdso, signal_trampoline),
 #endif
 	.setup_rt_frame	= setup_rt_frame,
+	.rt_signal_return_offset =
+		offsetof(struct mips_vdso, rt_signal_trampoline),
 	.restart	= __NR_restart_syscall
 };
 
···
 	struct k_sigaction *ka, sigset_t *oldset, struct pt_regs *regs)
 {
 	int ret;
+	struct mips_abi *abi = current->thread.abi;
+	void *vdso = current->mm->context.vdso;
 
 	switch(regs->regs[0]) {
 	case ERESTART_RESTARTBLOCK:
···
 	regs->regs[0] = 0;		/* Don't deal with this again.  */
 
 	if (sig_uses_siginfo(ka))
-		ret = current->thread.abi->setup_rt_frame(ka, regs, sig, oldset, info);
+		ret = abi->setup_rt_frame(vdso + abi->rt_signal_return_offset,
+					  ka, regs, sig, oldset, info);
 	else
-		ret = current->thread.abi->setup_frame(ka, regs, sig, oldset);
+		ret = abi->setup_frame(vdso + abi->signal_return_offset,
+				       ka, regs, sig, oldset);
 
 	spin_lock_irq(&current->sighand->siglock);
 	sigorsets(&current->blocked, &current->blocked, &ka->sa.sa_mask);

arch/mips/kernel/signal32.c

···
 #include <asm/system.h>
 #include <asm/fpu.h>
 #include <asm/war.h>
+#include <asm/vdso.h>
 
 #include "signal-common.h"
 
···
 /*
  * Including <asm/unistd.h> would give use the 64-bit syscall numbers ...
  */
-#define __NR_O32_sigreturn		4119
-#define __NR_O32_rt_sigreturn		4193
 #define __NR_O32_restart_syscall        4253
 
 /* 32-bit compatibility types */
···
 	compat_sigset_t     uc_sigmask;   /* mask last for extensibility */
 };
 
-/*
- * Horribly complicated - with the bloody RM9000 workarounds enabled
- * the signal trampolines is moving to the end of the structure so we can
- * increase the alignment without breaking software compatibility.
- */
-#if ICACHE_REFILLS_WORKAROUND_WAR == 0
-
 struct sigframe32 {
 	u32 sf_ass[4];		/* argument save space for o32 */
-	u32 sf_code[2];		/* signal trampoline */
+	u32 sf_pad[2];		/* Was: signal trampoline */
 	struct sigcontext32 sf_sc;
 	compat_sigset_t sf_mask;
 };
 
 struct rt_sigframe32 {
 	u32 rs_ass[4];			/* argument save space for o32 */
-	u32 rs_code[2];			/* signal trampoline */
+	u32 rs_pad[2];			/* Was: signal trampoline */
 	compat_siginfo_t rs_info;
 	struct ucontext32 rs_uc;
 };
-
-#else  /* ICACHE_REFILLS_WORKAROUND_WAR */
-
-struct sigframe32 {
-	u32 sf_ass[4];			/* argument save space for o32 */
-	u32 sf_pad[2];
-	struct sigcontext32 sf_sc;	/* hw context */
-	compat_sigset_t sf_mask;
-	u32 sf_code[8] ____cacheline_aligned;	/* signal trampoline */
-};
-
-struct rt_sigframe32 {
-	u32 rs_ass[4];			/* argument save space for o32 */
-	u32 rs_pad[2];
-	compat_siginfo_t rs_info;
-	struct ucontext32 rs_uc;
-	u32 rs_code[8] __attribute__((aligned(32)));	/* signal trampoline */
-};
-
-#endif	/* !ICACHE_REFILLS_WORKAROUND_WAR */
 
 /*
  * sigcontext handlers
···
 	force_sig(SIGSEGV, current);
 }
 
-static int setup_frame_32(struct k_sigaction * ka, struct pt_regs *regs,
-	int signr, sigset_t *set)
+static int setup_frame_32(void *sig_return, struct k_sigaction *ka,
+			  struct pt_regs *regs, int signr, sigset_t *set)
 {
 	struct sigframe32 __user *frame;
 	int err = 0;
···
 	frame = get_sigframe(ka, regs, sizeof(*frame));
 	if (!access_ok(VERIFY_WRITE, frame, sizeof (*frame)))
 		goto give_sigsegv;
-
-	err |= install_sigtramp(frame->sf_code, __NR_O32_sigreturn);
 
 	err |= setup_sigcontext32(regs, &frame->sf_sc);
 	err |= __copy_conv_sigset_to_user(&frame->sf_mask, set);
···
 	regs->regs[ 5] = 0;
 	regs->regs[ 6] = (unsigned long) &frame->sf_sc;
 	regs->regs[29] = (unsigned long) frame;
-	regs->regs[31] = (unsigned long) frame->sf_code;
+	regs->regs[31] = (unsigned long) sig_return;
 	regs->cp0_epc = regs->regs[25] = (unsigned long) ka->sa.sa_handler;
 
 	DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
···
 	return -EFAULT;
 }
 
-static int setup_rt_frame_32(struct k_sigaction * ka, struct pt_regs *regs,
-	int signr, sigset_t *set, siginfo_t *info)
+static int setup_rt_frame_32(void *sig_return, struct k_sigaction *ka,
+			     struct pt_regs *regs, int signr, sigset_t *set,
+			     siginfo_t *info)
 {
 	struct rt_sigframe32 __user *frame;
 	int err = 0;
···
 	frame = get_sigframe(ka, regs, sizeof(*frame));
 	if (!access_ok(VERIFY_WRITE, frame, sizeof (*frame)))
 		goto give_sigsegv;
-
-	err |= install_sigtramp(frame->rs_code, __NR_O32_rt_sigreturn);
 
 	/* Convert (siginfo_t -> compat_siginfo_t) and copy to user. */
 	err |= copy_siginfo_to_user32(&frame->rs_info, info);
···
 	regs->regs[ 5] = (unsigned long) &frame->rs_info;
 	regs->regs[ 6] = (unsigned long) &frame->rs_uc;
 	regs->regs[29] = (unsigned long) frame;
-	regs->regs[31] = (unsigned long) frame->rs_code;
+	regs->regs[31] = (unsigned long) sig_return;
 	regs->cp0_epc = regs->regs[25] = (unsigned long) ka->sa.sa_handler;
 
 	DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
···
  */
 struct mips_abi mips_abi_32 = {
 	.setup_frame	= setup_frame_32,
+	.signal_return_offset =
+		offsetof(struct mips_vdso, o32_signal_trampoline),
 	.setup_rt_frame	= setup_rt_frame_32,
+	.rt_signal_return_offset =
+		offsetof(struct mips_vdso, o32_rt_signal_trampoline),
 	.restart	= __NR_O32_restart_syscall
 };
 

arch/mips/kernel/signal_n32.c

···
 #include <asm/fpu.h>
 #include <asm/cpu-features.h>
 #include <asm/war.h>
+#include <asm/vdso.h>
 
 #include "signal-common.h"
 
 /*
  * Including <asm/unistd.h> would give use the 64-bit syscall numbers ...
  */
-#define __NR_N32_rt_sigreturn		6211
 #define __NR_N32_restart_syscall	6214
 
 extern int setup_sigcontext(struct pt_regs *, struct sigcontext __user *);
···
 	compat_sigset_t     uc_sigmask;   /* mask last for extensibility */
 };
 
-#if ICACHE_REFILLS_WORKAROUND_WAR == 0
-
 struct rt_sigframe_n32 {
 	u32 rs_ass[4];			/* argument save space for o32 */
-	u32 rs_code[2];			/* signal trampoline */
+	u32 rs_pad[2];			/* Was: signal trampoline */
 	struct compat_siginfo rs_info;
 	struct ucontextn32 rs_uc;
 };
-
-#else  /* ICACHE_REFILLS_WORKAROUND_WAR */
-
-struct rt_sigframe_n32 {
-	u32 rs_ass[4];			/* argument save space for o32 */
-	u32 rs_pad[2];
-	struct compat_siginfo rs_info;
-	struct ucontextn32 rs_uc;
-	u32 rs_code[8] ____cacheline_aligned;		/* signal trampoline */
-};
-
-#endif	/* !ICACHE_REFILLS_WORKAROUND_WAR */
 
 extern void sigset_from_compat(sigset_t *set, compat_sigset_t *compat);
 
···
 	force_sig(SIGSEGV, current);
 }
 
-static int setup_rt_frame_n32(struct k_sigaction * ka,
+static int setup_rt_frame_n32(void *sig_return, struct k_sigaction *ka,
 	struct pt_regs *regs, int signr, sigset_t *set, siginfo_t *info)
 {
 	struct rt_sigframe_n32 __user *frame;
···
 	frame = get_sigframe(ka, regs, sizeof(*frame));
 	if (!access_ok(VERIFY_WRITE, frame, sizeof (*frame)))
 		goto give_sigsegv;
-
-	install_sigtramp(frame->rs_code, __NR_N32_rt_sigreturn);
 
 	/* Create siginfo.  */
 	err |= copy_siginfo_to_user32(&frame->rs_info, info);
···
 	regs->regs[ 5] = (unsigned long) &frame->rs_info;
 	regs->regs[ 6] = (unsigned long) &frame->rs_uc;
 	regs->regs[29] = (unsigned long) frame;
-	regs->regs[31] = (unsigned long) frame->rs_code;
+	regs->regs[31] = (unsigned long) sig_return;
 	regs->cp0_epc = regs->regs[25] = (unsigned long) ka->sa.sa_handler;
 
 	DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
···
 
 struct mips_abi mips_abi_n32 = {
 	.setup_rt_frame	= setup_rt_frame_n32,
+	.rt_signal_return_offset =
+		offsetof(struct mips_vdso, n32_rt_signal_trampoline),
 	.restart	= __NR_N32_restart_syscall
 };