[PATCH] libctf,libsframe: remove include of config.h

[Indu Bhagat]

On 2026-08-11 09:18, Andrew Burgess wrote:
> While testing the upcoming GDB 18 release an issue was reported
> relating to libsframe/sframe.c and its use of libctf/swap.h.  The
> original report can be found here:
> 
>    https://inbox.sourceware.org/gdb-patches/865x1j1z61.fsf@gnu.org
> 
> What happens is that during the first build of GDB everything builds
> fine without any warnings.  But if for any reason we need to recompile
> libsframe/sframe.c then we would see compiler warnings like this:
> 
>         CC       libsframe_la-sframe.lo
>       In file included from ./../libctf/swap.h:23,
>                        from sframe.c:27:
>       ./../libctf/config.h:127: warning: "PACKAGE" redefined
>         127 | #define PACKAGE "libctf"
>             |
> 
> This is just one of the warnings, we actually get many similar
> warnings for the various things defined in libctf/config.h.
> 
> After investigation I discovered that this issue only occurs when
> building in the source tree.
> 
> Here's what happens, starting from a clean source tree.
> 
>  From Makefile.def we see that the 'all-bfd' target depends on
> 'all-libsframe', and the 'configure-libctf' target depends on
> 'all-bfd'.  The dependency chain then is:
> 
>    all-libsframe  →  all-bfd  →  configure-libctf
> 
> This means that, when libsframe is first built libctf/config.h will
> not yet have been created by the configure-libctf build target.  Due
> to the include search paths added to the gcc compilation command, the
> include of config.h from libctf/swap.h will be satisfied by
> libsframe/config.h.
> 
> If we allow the 'configure-libctf' target to complete then
> libctf/config.h will be created.
> 
> If we now recompile libsframe/sframe.c then we run into the problem,
> sframe.c includes config.h which will be satisfied by
> libsframe/config.h, and then sframe.c includes libctf/swap.h which
> also includes config.h.
> 
> However, now libctf/config.h exists, and this is used to satisfy the
> include from swap.h, this is a different config.h than was used in the
> original build, and conflicts with the config.h included from
> sframe.c.
> 
> Here are exact steps to reproduce:
> 
>    cd /path/to/binutils-gdb/src
>    ./configure
>    make configure-libctf
>    touch libsframe/sframe.c
>    make all-libsframe
> 
> I considered two possible fixes for this issue.
> 
> Currently the includes are written as: #include "config.h".  The use
> of quotes around the file name mean gcc will first check the directory
> of the including file and will then check the paths passed using -I to
> the compiler.  This is why we find libctf/config.h.
> 
> If we switch to: #include <config.h> then we skip the check of the
> source directory, and go straight to checking the -I paths.  When
> compiling libsframe/sframe.c this will mean we find libsframe/config.h
> first, which does indeed fix the issue.
> 
> However, in most cases we would expect the main source file to already
> pull in config.h, so it feels easier to just make that the requirement
> and remove the include of config.h from libctf/swap.h.
> 
> Removing the include of config.h seemed risky so I looked at all the
> files currently pulling in libctf/swap.h, there are not many:
> 
> libctf/ctf-endian.h:
>    - Includes config.h before including swap.h
> 
> libctf/ctf-open-bfd.c:
> libctf/ctf-open.c:
>    - Both include ctf-impl.h, which includes config.h before including
>      swap.h
> 
> libsframe/sframe.c:
>    - This is our problem case, pulls in its own local config.h before
>      including libctf/swap.h.
> 
> So I think making this change should be safe, and resolves the
> warnings when performing an in tree build.
> ---
>   libctf/swap.h | 1 -
>   1 file changed, 1 deletion(-)
> 
> diff --git a/libctf/swap.h b/libctf/swap.h
> index 15cc61c8b59..d23f5895ad2 100644
> --- a/libctf/swap.h
> +++ b/libctf/swap.h
> @@ -20,7 +20,6 @@
>   #ifndef _CTF_SWAP_H
>   #define _CTF_SWAP_H
>   
> -#include "config.h"
>   #include <stdint.h>
>   #include <assert.h>
>   
> 
> base-commit: a80fede20bc1330eca5e419392c6595bb3a6ac1d

Thanks for working on this Andrew.

(CC'ing CTF maintainer Nick Alcock as well)

While current usages of swap.h in libctf/ will do fine with this change, 
I am concerned for posterity because if any future user of swap.h does 
not include ctf-impl.h or config.h, it may lead to undesirable outcomes 
(unintended usage of swap.h definitions when those from byteswap.h 
exist, etc ?).

Previously, this issue of libsframe smuggling in the swap.h from libctf 
has been raised before in a different context, but a suggestion was to 
move this code to libiberty 
https://sourceware.org/bugzilla/show_bug.cgi?id=30588

(For the short term) A possibility is to duplicate this header in 
libsframe and at least keep the two directories not cross-use. I will 
send a patch shortly for this adding a local copy (say, 
libsframe/sframe-swap.h) and removing -I$(srcdir)/../libctf from 
libsframe/Makefile.am. This will keep libsframe cleanly decoupled 
without altering libctf/swap.h.

Another option is to move the swap.h related functions to a common place 
like include/ in binutils so libsframe, libctf (and elfcpp?) can use it.

Thoughts on what the best long term position will be ?