For ia32 PIC, the first thing of many syscalls does is to call
__x86.get_pc_thunk.reg to load PC into reg in case there is an error,
which is required for setting errno. In most cases, there are no
errors. But we still call __x86.get_pc_thunk.reg. This patch adds
INLINE_SYSCALL_ERROR_RETURN_VALUE so that i386 can optimize setting
errno by branching to the internal __syscall_error without PLT.
With i386 INLINE_SYSCALL_ERROR_RETURN_VALUE and i386 syscall inlining
optimization for GCC 5, for sysdeps/unix/sysv/linux/fchmodat.c with
-O2 -march=i686 -mtune=generic, GCC 5.2 now generates:
<fchmodat>:
0: push %ebx
1: mov 0x14(%esp),%eax
5: mov 0x8(%esp),%ebx
9: mov 0xc(%esp),%ecx
d: mov 0x10(%esp),%edx
11: test $0xfffffeff,%eax
16: jne 38 <fchmodat+0x38>
18: test $0x1,%ah
1b: jne 48 <fchmodat+0x48>
1d: mov $0x132,%eax
22: call *%gs:0x10
29: cmp $0xfffff000,%eax
2e: ja 58 <fchmodat+0x58>
30: pop %ebx
31: ret
32: lea 0x0(%esi),%esi
38: pop %ebx
39: mov $0xffffffea,%eax
3e: jmp 3f <fchmodat+0x3f> 3f: R_386_PC32 __syscall_error
43: nop
44: lea 0x0(%esi,%eiz,1),%esi
48: pop %ebx
49: mov $0xffffffa1,%eax
4e: jmp 4f <fchmodat+0x4f> 4f: R_386_PC32 __syscall_error
53: nop
54: lea 0x0(%esi,%eiz,1),%esi
58: pop %ebx
59: jmp 5a <fchmodat+0x5a> 5a: R_386_PC32 __syscall_error