Date: Tue, 21 Jan 2020 11:05:37 -0500
From: Steve Grubb <sgrubb(a)redhat.com>
Subject: Re: gcc 10: Default to -fno-common, multiple definitions of
...
To: devel(a)lists.fedoraproject.org
Cc: Jakub Jelinek <jakub(a)redhat.com>
Message-ID: <4127758.jL2Gs7s9Fr@x2>
Content-Type: text/plain; charset="UTF-8"
On Tuesday, January 21, 2020 7:35:03 AM EST Miro Hrončok wrote:
> This is a known thing in gcc 10:
>
>
https://gcc.gnu.org/gcc-10/porting_to.html#common
>
> "Default to -fno-common
>
> A common mistake in C is omitting extern when declaring a global variable
> in a header file. If the header is included by several files it results in
> multiple definitions of the same variable. In previous GCC versions this
> error is ignored. GCC 10 defaults to -fno-common, which means a linker
> error will now be reported. To fix this, use extern in header files when
> declaring global variables, and ensure each global is defined in exactly
> one C file. As a workaround, legacy C code can be compiled with -fcommon.
>
>
> int x; // tentative definition - avoid in header files
>
> extern int y; // correct declaration in a header file"
So, for those of us using F31 as the development / test environment, is there
a macro that we can add -fno-common to in ~/.rpmmacros without placing it in
the %__global_compiler_flags in /usr/lib/rpm/redhat/macros ?
Looking for an easy way to reproduce this without modifying root owned files.
-Steve
------------------------------
Date: Tue, 21 Jan 2020 17:27:20 +0100
From: Miro Hrončok <mhroncok(a)redhat.com>
Subject: Re: gcc 10: Default to -fno-common, multiple definitions of
...
To: Steve Grubb <sgrubb(a)redhat.com>, devel(a)lists.fedoraproject.org
Message-ID: <0f655139-44f5-a0c5-b600-66614c8bd6d6(a)redhat.com>
Content-Type: text/plain; charset=utf-8; format=flowed
On 21. 01. 20 17:05, Steve Grubb wrote:
> On Tuesday, January 21, 2020 7:35:03 AM EST Miro Hrončok wrote:
> > This is a known thing in gcc 10:
> >
> >
https://gcc.gnu.org/gcc-10/porting_to.html#common
> >
> > "Default to -fno-common
> >
> > A common mistake in C is omitting extern when declaring a global variable
> > in a header file. If the header is included by several files it results in
> > multiple definitions of the same variable. In previous GCC versions this
> > error is ignored. GCC 10 defaults to -fno-common, which means a linker
> > error will now be reported. To fix this, use extern in header files when
> > declaring global variables, and ensure each global is defined in exactly
> > one C file. As a workaround, legacy C code can be compiled with -fcommon.
> >
> >
> > int x; // tentative definition - avoid in header files
> >
> > extern int y; // correct declaration in a header file"
>
> So, for those of us using F31 as the development / test environment, is there
> a macro that we can add -fno-common to in ~/.rpmmacros without placing it in
> the %__global_compiler_flags in /usr/lib/rpm/redhat/macros ?
>
> Looking for an easy way to reproduce this without modifying root owned files.
You should be able to redefine %__global_compiler_flags in ~/.rpmmacros.
It still means you need to copy paste the current flags, but you won't need to
touch root owned files.
I proposed a change to redhat-rpm-config to handle this
case by
allowing package to add a single line to their .spec file to turn off
the new common symbol handling. Igor rejected that change arguing that
the packages themselves should be fixed.
Jeff