Re: RFC: [PATCH] Add INLINE_SYSCALL_ERROR_RETURN

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sat, Aug 22, 2015 at 4:24 AM, Florian Weimer <fw@deneb.enyo.de> wrote:
> * H. J. Lu:
>
>> 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 so that i386 can optimize setting errno by
>> branching to the internal __syscall_error without PLT.
>>
>> With i386 INLINE_SYSCALL_ERROR_RETURN 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:
>
> The patch does not seem to contain the i386 optimized
> INLINE_SYSCALL_ERROR_RETURN definition.

The followup patch is at

https://sourceware.org/git/?p=glibc.git;a=commit;h=47213b3c76a4e21f490bcc0ad1e7d5ca7cf93120

which contains:

+#if IS_IN (libc)
+# define INLINE_SYSCALL(name, nr, args...) \
+  ({      \
+    unsigned int resultvar = INTERNAL_SYSCALL (name, , nr, args);      \
+    __glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (resultvar, ))      \
+    ? __syscall_error (-INTERNAL_SYSCALL_ERRNO (resultvar, ))      \
+    : (int) resultvar; })

and

+/* Set error number and return -1.  Return the internal function,
+   __syscall_error, which sets errno from the negative error number
+   and returns -1, to avoid PIC.  */
+#undef INLINE_SYSCALL_ERROR_RETURN
+#define INLINE_SYSCALL_ERROR_RETURN(resultvar) \
+  __syscall_error (-(resultvar))

-- 
H.J.