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Date: Thu, 15 Oct 2015 13:13:39 -0700
Message-ID: 
 <CAMe9rOriWgkdxLUx1+Rt8kh7Uguwa9ka_HeJia5-Gpm+7iLVOg@mail.gmail.com>
Subject: Re: [PATCH 5/6] Optimize i386 syscall inlining
From: "H.J. Lu" <hjl.tools@gmail.com>
To: Roland McGrath <roland@hack.frob.com>
Cc: GNU C Library <libc-alpha@sourceware.org>

On Thu, Oct 15, 2015 at 12:54 PM, Roland McGrath <roland@hack.frob.com> wrote:
> This needs comments explaining why the compiler version conditional
> makes sense.

How about this?

diff --git a/sysdeps/unix/sysv/linux/i386/sysdep.h
b/sysdeps/unix/sysv/linux/i386/sysdep.h
index 5324da6..76db7b8 100644
--- a/sysdeps/unix/sysv/linux/i386/sysdep.h
+++ b/sysdeps/unix/sysv/linux/i386/sysdep.h
@@ -227,6 +227,10 @@
 extern int __syscall_error (int)
   attribute_hidden __attribute__ ((__regparm__ (1)));

+/* Since GCC 5 and above can properly spill %ebx with PIC when needed,
+   we can inline syscalls with 6 arguments if GCC 5 or above is used
+   to compile glibc.  */
+
 #if !__GNUC_PREREQ (5,0)
 /* We need some help from the assembler to generate optimal code.  We
    define some macros here which later will be used.  */