GNU bug report logs - #66002
[PATCH] build: suppress suggest-attribute=cold warnings

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Gleb Fotengauer-Malinovskiy <glebfm <at> altlinux.org>
To: bug-grep <at> gnu.org
Cc: Gleb Fotengauer-Malinovskiy <glebfm <at> altlinux.org>
Subject: [PATCH] build: suppress suggest-attribute=cold warnings
Date: Fri, 15 Sep 2023 13:45:00 +0000

Following the glibc commit glibc-2.38~298 ("Mark various cold functions
as __COLD"), GNU grep build with -flto flag triggers a GCC warning:

sigsegv.c: In function ‘stackoverflow_deinstall_handler.part.0’:
sigsegv.c:1441:1: error: function might be candidate for attribute ‘cold’ [-Werror=suggest-attribute=cold]

* configure.ac (GNULIB_WARN_CFLAGS): Suppress -Wsuggest-attribute=cold.

Tiny-change: yes
---
 configure.ac | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/configure.ac b/configure.ac
index 844a259bd..b793cabde 100644
--- a/configure.ac
+++ b/configure.ac
@@ -159,6 +159,11 @@ if test $gl_gcc_warnings != no; then
   # Remove the following and save the result in GNULIB_WARN_CFLAGS.
   nw=
   nw="$nw -Wunused-macros"
+
+  # To prevent warnings in sigsegv.c if the perror function
+  # has "cold" attribute.
+  nw="$nw -Wsuggest-attribute=cold"
+
   gl_WARN_ADD([-Wno-format-nonliteral])
   gl_MANYWARN_COMPLEMENT([GNULIB_WARN_CFLAGS], [$WARN_CFLAGS], [$nw])
   AC_SUBST([GNULIB_WARN_CFLAGS])
-- 
glebfm

Message #8 received at 66002 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Gleb Fotengauer-Malinovskiy <glebfm <at> altlinux.org>, 66002 <at> debbugs.gnu.org
Subject: Re: bug#66002: [PATCH] build: suppress suggest-attribute=cold warnings
Date: Fri, 15 Sep 2023 17:04:05 -0700

On 9/15/23 08:45, Gleb Fotengauer-Malinovskiy wrote:
> Following the glibc commit glibc-2.38~298 ("Mark various cold functions
> as __COLD"), GNU grep build with -flto flag triggers a GCC warning:
> 
> sigsegv.c: In function ‘stackoverflow_deinstall_handler.part.0’:
> sigsegv.c:1441:1: error: function might be candidate for attribute ‘cold’ [-Werror=suggest-attribute=cold]
> 
> * configure.ac (GNULIB_WARN_CFLAGS): Suppress -Wsuggest-attribute=cold.

I'm not seeing this problem on Fedora 38 when I manually mark error, 
error_at_line, and perror with _GL_ATTRIBUTE_COLD. I am compiling with 
gcc (GCC) 13.2.1 20230728 (Red Hat 13.2.1-1) and configuring with 
"./configure --enable-gcc-warnings 'CC=gcc -flto'". This is grep commit 
102be2bfa571355ff44db39348438a0def1ab382.

If you're using an older GCC, I wouldn't worry about the false alarm, 
whatever it's about (it's not clear from the diagnostic). The 
attribute-cold diagnostics are occasionally helpful for minor 
performance tuning, and are harmless if ignored.

Message #11 received at 66002 <at> debbugs.gnu.org (full text, mbox):

From: Gleb Fotengauer-Malinovskiy <glebfm <at> altlinux.org>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 66002 <at> debbugs.gnu.org
Subject: Re: bug#66002: [PATCH] build: suppress suggest-attribute=cold warnings
Date: Sun, 17 Sep 2023 01:28:53 +0400

On Fri, Sep 15, 2023 at 05:04:05PM -0700, Paul Eggert wrote:
> On 9/15/23 08:45, Gleb Fotengauer-Malinovskiy wrote:
> > Following the glibc commit glibc-2.38~298 ("Mark various cold functions
> > as __COLD"), GNU grep build with -flto flag triggers a GCC warning:
> > 
> > sigsegv.c: In function ‘stackoverflow_deinstall_handler.part.0’:
> > sigsegv.c:1441:1: error: function might be candidate for attribute ‘cold’ [-Werror=suggest-attribute=cold]
> > 
> > * configure.ac (GNULIB_WARN_CFLAGS): Suppress -Wsuggest-attribute=cold.
> 
> I'm not seeing this problem on Fedora 38 when I manually mark error, 
> error_at_line, and perror with _GL_ATTRIBUTE_COLD. I am compiling with 
> gcc (GCC) 13.2.1 20230728 (Red Hat 13.2.1-1) and configuring with 
> "./configure --enable-gcc-warnings 'CC=gcc -flto'". This is grep commit 
> 102be2bfa571355ff44db39348438a0def1ab382.
> 
> If you're using an older GCC,

I've encountered this warning with a version of GCC that's very similar:
gcc-13 (GCC) 13.2.1 20230817 (ALT Sisyphus 13.2.1-alt2)

I'm not certain what's different in our testing, but I managed to
reproduce it on Fedora 38.  This occurred both when I made a simple edit
to the /usr/include/stdio.h header:
-extern void perror (const char *__s);
+extern void perror (const char *__s) __attribute__ ((__cold__));
and with glibc version 2.38.9000-8.fc40.x86_64 from Rawhide.

> I wouldn't worry about the false alarm, 
> whatever it's about (it's not clear from the diagnostic). The 
> attribute-cold diagnostics are occasionally helpful for minor 
> performance tuning, and are harmless if ignored.

I'm not insisting that this needs to be addressed, but I do believe that
someone else might encounter this issue.

-- 
glebfm

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