Re: [PATCH] Modify align-c/align-c++ test case for AIX

[Pedro Alves <pedro@palves.net>]

On 2023-03-21 7:41 a.m., Ulrich Weigand via Gdb-patches wrote:
> Aditya Kamath1 <Aditya.Kamath1@ibm.com> wrote:
> 
>> So clearly, linker optimises out unused global variables. More about the
>> same can be read in the documentation
>> {https://www.ibm.com/docs/en/aix/7.1?topic=l-ld-command } 
> 
> I see the -Wl,-bnogc option there, this makes sense.
> 
> I'm not sure why "-lodm -lcfg" should be necessary as well, this
> doesn't really appear related to me.  Can you try without those?
> 
> 
>> So I was thinking if we can pass these to our site.exp file if the target is AIX:
>>
>> set CC_FOR_TARGET "/opt/freeware/bin/gcc"
>> set CXX_FOR_TARGET "/opt/freeware/bin/g++"
>> set CXXFLAGS_FOR_TARGET "-O0 -w -g -gdwarf -maix64"
>> set CFLAGS_FOR_TARGET "-O0 -w -g -gdwarf -maix64"
>>
>> with the options -Wl,-bnogc  -lodm -lcfg. 
>>
>> We also use -maix32 for testing in 32 bit mode as well. 
>>
>> I think this would be a better patch and in AIX we will not be seeing
>> so many failures as we see now instead of the initial proposed ifdef patch.
>> Only thing is we need to add this in a file which I am not aware of such
>> that if the target is AIX we need to add these flags in the site.exp
>> file so that while running test cases we get this file to pass these flags
>> during the compilation of them. 
> 
> If the -bnogc flag is always necessary with the AIX linker, this
> should be handled automatically by the test instead of via site.exp.
> 
> I'm assuming this is only needed with test files that use global
> variables unused in the source code, but used by the debugger.
> I think it would be best to explicitly add the flag to those tests
> where it is needed.

I'm wondering whether __attribute__((used)) on the global variable makes any
difference.  IIRC with LLVM it prevents link-time stripping on Mach-O and PE/COFF,
but I don't know about XCOFF + GCC.  (It doesn't on ELF, you
need 'retain' for that.)

Pedro Alves

> 
> For example, for the align-c tests, you can change the beginning
> of run_alignment_test in gdb.base/align.exp.tcl to something like:
> 
>     set flags {debug}
>     if { "$lang" == "c++" } {
>         lappend flags "additional_flags=-std=c++11"
>     }
>     if { [istarget *-*-aix*] } {
>         # Disable linker garbage collection to avoid optimizing
>         # out global variables unused in the test source code.
>         lappend flags "ldflags=-Wl,-bnogc"
>     }
>     standard_testfile $filename
>     if {[prepare_for_testing "failed to prepare" "$testfile" $srcfile $flags]} {
>         return -1
>     }
> 
> Bye,
> Ulrich
>