Re: [PATCH] Fix AIX build break

[Tom de Vries <tdevries@suse.de>]

On 1/12/24 10:20, Aditya Kamath1 wrote:
> Respected community members,
> 
> Hi,
> 
> Our CI in AIX for GDB has been broken for the last two days with the 
> following error.
> 
> CXXLD  gdb
> 
> ld: 0711-317 ERROR: Undefined symbol: _ZTH23deprecated_warning_hook
> 
> ld: 0711-317 ERROR: Undefined symbol: ._ZTH23deprecated_warning_hook
> 
> ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more 
> information.
> 
> collect2: error: ld returned 8 exit status
> 
> gmake: *** [Makefile:2184: gdb] Error 1
> 
> These symbols came due to the commit 
> https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=54b815ddb428944a70694e3767a0fadbdd9ca9ea <https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=54b815ddb428944a70694e3767a0fadbdd9ca9ea>
> 

I think this is triggered by using thread-local with extern.

I found this commit:
...
commit fece451c2aca57b095e7e4063e342781cf74aa75
Author: Christian Biesinger <cbiesinger@google.com>
Date:   Tue Mar 9 08:16:23 2021 -0600

     Use RAII to set the per-thread SIGSEGV handler

     This avoids using a thread-local extern variable, which causes link 
errors
     on some platforms, notably Cygwin.  But I think this is a better 
pattern
     even outside of working around linker bugs because it encapsulates 
direct
     access to the variable inside the class, instead of having a global 
extern
     variable.
...
which seems related, given that it mentions link errors.  Perhaps we can 
do something similar here.

Thanks,
- Tom

> The problem in AIX is marking a variable for thread storage as 
> thread_local that makes that symbol a weak symbol. The dump output of 
> the complaints.o shows this as pasted here:-
> 
> # dump -tov -X64 complaints.o | grep _ZTH23deprecated_warning_hook
> 
> [32]    m   0x00000000     undef     1    weak                    
> _ZTH23deprecated_warning_hook
> 
> [36]    m   0x00000000     undef     1    weak                    
> ._ZTH23deprecated_warning_hook
> 
> [3209]  m   0x000203d8     .data     1  unamex                    
> _ZTH23deprecated_warning_hook
> 
> Hence in the final stage of compilation while creating the binary gdb, 
> the ld error came and the compilation is unsuccessful since the symbol 
> is not visible though complaints.c file was successfully compiled.
> 
> This patch is a fix for the same where instead of thread_local we used 
> __thread and GDB now compiles in AIX. Please find attached the patch. 
> (See: 0001-Fix-AIX-build-break.patch).
> 
> I want to know your opinion about this. Also, I do not know the impact 
> of this change on other targets. If we can do this better, kindly let me 
> know.
> 
> Have a nice day ahead.
> 
> Thanks and regards,
> Aditya.
>