Re: [PATCH v2] [gdb/testsuite] Fix gdb.base/enum_cond.exp on arm-linux

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

On 3/18/25 14:46, Simon Marchi wrote:
> 
> 
> On 2025-03-18 03:28, Tom de Vries wrote:
>> On arm-linux, I run into:
>> ...
>> gdb compile failed, ld: warning: enum_cond.o uses variable-size enums yet \
>>    the output is to use 32-bit enums; use of enum values across objects may fail
>> UNTESTED: gdb.base/enum_cond.exp: failed to compile
>> ...
>>
>> Fix this by using -nostdlib.
>>
>> Tested on arm-linux and x86_64-linux.
>> ---
>>   gdb/testsuite/gdb.base/enum_cond.c   | 16 ++++++++++++++++
>>   gdb/testsuite/gdb.base/enum_cond.exp | 15 ++++++++++++++-
>>   gdb/testsuite/lib/gdb.exp            | 12 ++++++++++++
>>   3 files changed, 42 insertions(+), 1 deletion(-)
>>
>> diff --git a/gdb/testsuite/gdb.base/enum_cond.c b/gdb/testsuite/gdb.base/enum_cond.c
>> index 35e126aed45..df8830f0c9e 100644
>> --- a/gdb/testsuite/gdb.base/enum_cond.c
>> +++ b/gdb/testsuite/gdb.base/enum_cond.c
>> @@ -46,3 +46,19 @@ main (void)
>>     return 0;
>>   }
>>   
>> +void
>> +exit (int status)
>> +{
>> +#if HAVE_BUILTIN_TRAP
>> +  __builtin_trap ();
>> +#endif
>> +  while (1)
>> +    ;
> 
> Huh, it would be nice to find something that works everywhere.
> We do
> have "my_exit" in lib/my-syscalls.h, which we could call, but we would
> need to provide a syscall implementation for all arches we want to test
> (not too hard, but still).
> 
> What about having a global:
> 
>    volatile int *dummy = nullptr;
> 
> and then do:
> 
>    *dummy = 1;
> 
> Would that successfully stop the program on all known platforms?

AFAIU that's undefined behaviour, so a valid implementation might just 
skip the store.

I can submit a v3 using this (note NULL instead of nullptr since this is 
C, not C++):
...
void
exit (int status)
{
#if HAVE_BUILTIN_TRAP
   __builtin_trap ();
#endif

   {
     volatile int *dummy = NULL;
     *dummy = 1;
   }

   while (1)
     ;
...
but AFAIC I'm fine with this v2.

Thanks,
- Tom