x86/entry/vdso32: Remove SYSCALL_ENTER_KERNEL macro in sigreturn.S

A macro SYSCALL_ENTER_KERNEL was defined in sigreturn.S, with the
ability of overriding it. The override capability, however, is not
used anywhere, and the macro name is potentially confusing because it
seems to imply that sysenter/syscall could be used here, which is NOT
true: the sigreturn system calls MUST use int $0x80.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://patch.msgid.link/20251216212606.1325678-6-hpa@zytor.com

Author: H. Peter Anvin

arch/x86/entry/vdso/vdso32/sigreturn.S

@@ -3,10 +3,6 @@
 #include <asm/unistd_32.h>
 #include <asm/asm-offsets.h>
 
-#ifndef SYSCALL_ENTER_KERNEL
-#define	SYSCALL_ENTER_KERNEL	int $0x80
-#endif
-
 	.text
 	.globl __kernel_sigreturn
 	.type __kernel_sigreturn,@function
@@ -16,7 +12,7 @@ __kernel_sigreturn:
 .LSTART_sigreturn:
 	popl %eax		/* XXX does this mean it needs unwind info? */
 	movl $__NR_sigreturn, %eax
-	SYSCALL_ENTER_KERNEL
+	int $0x80
 .LEND_sigreturn:
 SYM_INNER_LABEL(vdso32_sigreturn_landing_pad, SYM_L_GLOBAL)
 	nop
@@ -28,7 +24,7 @@ SYM_INNER_LABEL(vdso32_sigreturn_landing_pad, SYM_L_GLOBAL)
 __kernel_rt_sigreturn:
 .LSTART_rt_sigreturn:
 	movl $__NR_rt_sigreturn, %eax
-	SYSCALL_ENTER_KERNEL
+	int $0x80
 .LEND_rt_sigreturn:
 SYM_INNER_LABEL(vdso32_rt_sigreturn_landing_pad, SYM_L_GLOBAL)
 	nop