x86/asm/entry: Untangle 'system_call' into two entry points: entry_SYSCALL_64 and entry_INT80_32

The 'system_call' entry points differ starkly between native 32-bit and 64-bit
kernels: on 32-bit kernels it defines the INT 0x80 entry point, while on
64-bit it's the SYSCALL entry point.

This is pretty confusing when looking at generic code, and it also obscures
the nature of the entry point at the assembly level.

So unangle this by splitting the name into its two uses:

system_call (32) -> entry_INT80_32
system_call (64) -> entry_SYSCALL_64

As per the generic naming scheme for x86 system call entry points:

entry_MNEMONIC_qualifier

where 'qualifier' is one of _32, _64 or _compat.

Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/entry/entry_32.S

···
 ENDPROC(entry_SYSENTER_32)
 
 	# system call handler stub
-ENTRY(system_call)
+ENTRY(entry_INT80_32)
 	ASM_CLAC
 	pushl %eax			# save orig_eax
 	SAVE_ALL
···
 	lss (%esp), %esp		/* switch to espfix segment */
 	jmp restore_nocheck
 #endif
-ENDPROC(system_call)
+ENDPROC(entry_INT80_32)
 
 	# perform work that needs to be done immediately before resumption
 	ALIGN

arch/x86/entry/entry_64.S

···
  * with them due to bugs in both AMD and Intel CPUs.
  */
 
-ENTRY(system_call)
+ENTRY(entry_SYSCALL_64)
 	/*
 	 * Interrupts are off on entry.
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
···
 	 * after the swapgs, so that it can do the swapgs
 	 * for the guest and jump here on syscall.
 	 */
-GLOBAL(system_call_after_swapgs)
+GLOBAL(entry_SYSCALL_64_after_swapgs)
 
 	movq	%rsp,PER_CPU_VAR(rsp_scratch)
 	movq	PER_CPU_VAR(cpu_current_top_of_stack),%rsp
···
 
 	testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz tracesys
-system_call_fastpath:
+entry_SYSCALL_64_fastpath:
 #if __SYSCALL_MASK == ~0
 	cmpq $__NR_syscall_max,%rax
 #else
···
 	jnz tracesys_phase2		/* if needed, run the slow path */
 	RESTORE_C_REGS_EXCEPT_RAX	/* else restore clobbered regs */
 	movq ORIG_RAX(%rsp), %rax
-	jmp system_call_fastpath	/*      and return to the fast path */
+	jmp entry_SYSCALL_64_fastpath	/*      and return to the fast path */
 
 tracesys_phase2:
 	SAVE_EXTRA_REGS
···
 opportunistic_sysret_failed:
 	SWAPGS
 	jmp	restore_c_regs_and_iret
-END(system_call)
+END(entry_SYSCALL_64)
 
 
 	.macro FORK_LIKE func

arch/x86/include/asm/proto.h

···
 
 /* misc architecture specific prototypes */
 
-void system_call(void);
 void syscall_init(void);
 
-void entry_INT80_compat(void);
+void entry_SYSCALL_64(void);
 void entry_SYSCALL_compat(void);
+void entry_INT80_32(void);
+void entry_INT80_compat(void);
 void entry_SYSENTER_32(void);
 void entry_SYSENTER_compat(void);
 

arch/x86/kernel/cpu/common.c

···
 	 * set CS/DS but only a 32bit target. LSTAR sets the 64bit rip.
 	 */
 	wrmsrl(MSR_STAR,  ((u64)__USER32_CS)<<48  | ((u64)__KERNEL_CS)<<32);
-	wrmsrl(MSR_LSTAR, system_call);
+	wrmsrl(MSR_LSTAR, entry_SYSCALL_64);
 
 #ifdef CONFIG_IA32_EMULATION
 	wrmsrl(MSR_CSTAR, entry_SYSCALL_compat);

arch/x86/kernel/traps.c

···
 #else
 #include <asm/processor-flags.h>
 #include <asm/setup.h>
-
-asmlinkage int system_call(void);
+#include <asm/proto.h>
 #endif
 
 /* Must be page-aligned because the real IDT is used in a fixmap. */
···
 #endif
 
 #ifdef CONFIG_X86_32
-	set_system_trap_gate(IA32_SYSCALL_VECTOR, &system_call);
+	set_system_trap_gate(IA32_SYSCALL_VECTOR, entry_INT80_32);
 	set_bit(IA32_SYSCALL_VECTOR, used_vectors);
 #endif
 

arch/x86/xen/xen-asm_64.S

···
 /* Normal 64-bit system call target */
 ENTRY(xen_syscall_target)
 	undo_xen_syscall
-	jmp system_call_after_swapgs
+	jmp entry_SYSCALL_64_after_swapgs
 ENDPROC(xen_syscall_target)
 
 #ifdef CONFIG_IA32_EMULATION