x86/asm/entry: Untangle 'ia32_sysenter_target' into two entry points: entry_SYSENTER_32 and entry_SYSENTER_compat

So the SYSENTER instruction is pretty quirky and it has different behavior
depending on bitness and CPU maker.

Yet we create a false sense of coherency by naming it 'ia32_sysenter_target'
in both of the cases.

Split the name into its two uses:

ia32_sysenter_target (32) -> entry_SYSENTER_32
ia32_sysenter_target (64) -> entry_SYSENTER_compat

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

···
    the vsyscall page.  See vsyscall-sysentry.S, which defines the symbol.  */
 
 	# sysenter call handler stub
-ENTRY(ia32_sysenter_target)
+ENTRY(entry_SYSENTER_32)
 	movl TSS_sysenter_sp0(%esp),%esp
 sysenter_past_esp:
 	/*
···
 .popsection
 	_ASM_EXTABLE(1b,2b)
 	PTGS_TO_GS_EX
-ENDPROC(ia32_sysenter_target)
+ENDPROC(entry_SYSENTER_32)
 
 	# system call handler stub
 ENTRY(system_call)
···
 
 ENTRY(debug)
 	ASM_CLAC
-	cmpl $ia32_sysenter_target,(%esp)
+	cmpl $entry_SYSENTER_32,(%esp)
 	jne debug_stack_correct
 	FIX_STACK 12, debug_stack_correct, debug_esp_fix_insn
 debug_stack_correct:
···
 	popl %eax
 	je nmi_espfix_stack
 #endif
-	cmpl $ia32_sysenter_target,(%esp)
+	cmpl $entry_SYSENTER_32,(%esp)
 	je nmi_stack_fixup
 	pushl %eax
 	movl %esp,%eax
···
 	cmpl $(THREAD_SIZE-20),%eax
 	popl %eax
 	jae nmi_stack_correct
-	cmpl $ia32_sysenter_target,12(%esp)
+	cmpl $entry_SYSENTER_32,12(%esp)
 	je nmi_debug_stack_check
 nmi_stack_correct:
 	pushl %eax

arch/x86/entry/entry_64_compat.S

···
  * path below. We set up a complete hardware stack frame to share code
  * with the int 0x80 path.
  */
-ENTRY(ia32_sysenter_target)
+ENTRY(entry_SYSENTER_compat)
 	/*
 	 * Interrupts are off on entry.
 	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
···
 
 	RESTORE_EXTRA_REGS
 	jmp	sysenter_do_call
-ENDPROC(ia32_sysenter_target)
+ENDPROC(entry_SYSENTER_compat)
 
 /*
  * 32-bit SYSCALL instruction entry.

arch/x86/include/asm/proto.h

···
 
 void entry_INT80_compat(void);
 void entry_SYSCALL_compat(void);
-void ia32_sysenter_target(void);
+void entry_SYSENTER_32(void);
+void entry_SYSENTER_compat(void);
 
 void x86_configure_nx(void);
 void x86_report_nx(void);

arch/x86/kernel/cpu/common.c

···
 	      (unsigned long)tss + offsetofend(struct tss_struct, SYSENTER_stack),
 	      0);
 
-	wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long)ia32_sysenter_target, 0);
+	wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long)entry_SYSENTER_32, 0);
 
 out:
 	put_cpu();
···
 	 */
 	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
 	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
-	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)ia32_sysenter_target);
+	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
 #else
 	wrmsrl(MSR_CSTAR, ignore_sysret);
 	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);

arch/x86/xen/xen-asm_64.S

···
 /* 32-bit compat sysenter target */
 ENTRY(xen_sysenter_target)
 	undo_xen_syscall
-	jmp ia32_sysenter_target
+	jmp entry_SYSENTER_compat
 ENDPROC(xen_sysenter_target)
 
 #else /* !CONFIG_IA32_EMULATION */