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

[Simon Marchi <simark@simark.ca>]

On 3/18/25 10:08 AM, Tom de Vries wrote:
> 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

Ok, fair enough, that's a very edgy case anyway.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Simon