Re: [PATCH v3] gdb: align siginfo_t with the Linux kernel definition

[Matthieu Longo <matthieu.longo@arm.com>]

On 24/07/2026 10:18, Matthieu Longo wrote:

Sorry, the previous email left by mistake.

> On 23/07/2026 00:09, Luis wrote:
>> Hi Matthieu,
>>
>> On 22/07/2026 16:00, Matthieu Longo wrote:
>>> On 21/07/2026 22:09, Luis wrote:
>>>> On 02/07/2026 17:52, Matthieu Longo wrote:
>>> --- a/gdb/linux-tdep.c
>>> +++ b/gdb/linux-tdep.c
>>>>> +  append_composite_type_field (sigfault_union_type, "si_addr_lsb", short_type);
>>>>> +
>>>>> +  /* used when si_code=SEGV_BNDERR */
>>>>> +  type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
>>>>> +  append_composite_type_field (type, "_dummy_bnd", addr_bnd_pkey_padding_type);
>>>>> +  append_composite_type_field (type, "si_lower", void_ptr_type);
>>>>> +  append_composite_type_field (type, "si_upper", void_ptr_type);
>>>>> +  append_composite_type_field (sigfault_union_type, "_addr_bnd", type);
>>>>> +
>>>>> +  /* used when si_code=SEGV_PKUERR */
>>>>> +  type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
>>>>> +  append_composite_type_field (type, "_dummy_pkey", addr_bnd_pkey_padding_type);
>>>>> +  append_composite_type_field (type, "si_pkey", uint32_type);
>>>>> +  append_composite_type_field (sigfault_union_type, "_addr_pkey", type);
>>>>> +
>>>>> +  /* used when si_code=TRAP_PERF */
>>>>> +  type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
>>>>> +  append_composite_type_field (type, "si_perf_data", unsigned_long_type);
>>>>> +  append_composite_type_field (type, "si_perf_type", uint32_type);
>>>>> +  append_composite_type_field (type, "si_perf_flags", uint32_type);
>>>>> +  append_composite_type_field (sigfault_union_type, "_perf", type);
>>>>> +
>>>>> +  /* End _sigfault's anonymous union.  */
>>>>> +
>>>>> +  /* _sigfault is set by SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
>>>>>      type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
>>>>>      append_composite_type_field (type, "si_addr", void_ptr_type);
>>>>> +  /* Since there is no possibility to declare an anonymous union,
>>>>> +     using '_' instead.  */
>>>>> +  append_composite_type_field (type, "_", sigfault_union_type);
>>>>
>>>> Could we name this in a better way? Simply using _ is a bit strange.
>>>>
>>>
>>> What about "_union" ?
>>>
>>
>> Naming is hard. Given it is an anonymous union, should it have something anonymous in the name?
>>
> 
> I understand your point, but the name is going to start getting very lengthy.
> What about "_anon_union" ?
> 
>> If we're going to access this by hand, it might be worth having some easy to use too.
>>
> 
> What type of accessors do you have in mind ? Compile-time ones ? Or runtime ones at the destination
> of the GDB users when accessing _siginfo ?
> 
> For the compile-time ones, I propose to add those defines:
> --- a/gdb/linux-tdep.h
> +++ b/gdb/linux-tdep.h
> @@ -98,4 +98,18 @@ extern CORE_ADDR linux_get_hwcap2 ();
>  extern bool linux_address_in_shadow_stack_mem_range
>    (CORE_ADDR addr, std::pair<CORE_ADDR, CORE_ADDR> *range);
> 
> +/* How the fields from siginfo_t's _sigfault can be accessed.  */
> +#ifdef si_addr
> +#error "Matthieu: this should not happen"
> +#endif
> +#define si_addr       "_sifields._sigfault.si_addr"
> +#define si_trapno     "_sifields._sigfault._anon_union.si_trapno"
> +#define si_addr_lsb   "_sifields._sigfault._anon_union.si_addr_lsb"
> +#define si_lower      "_sifields._sigfault._anon_union._addr_bnd.si_lower"
> +#define si_upper      "_sifields._sigfault._anon_union._addr_bnd.si_upper"
> +#define si_pkey       "_sifields._sigfault._anon_union._addr_pkey.si_pkey"
> +#define si_perf_data  "_sifields._sigfault._anon_union._perf.si_perf_data"
> +#define si_perf_type  "_sifields._sigfault._anon_union._perf.si_perf_type"
> +#define si_perf_flags "_sifields._sigfault._anon_union._perf.si_perf_flags"
> +

This solution for accessors does not work because the si_* defines conflict with the ones from
/usr/include/aarch64-linux-gnu/bits/types/siginfo_t.h

I will come back to you with another approach that does not conflict with the linux kernel headers
(potentially with <signal.h> too).

Matthieu