Re: [PATCH v2] gdb: rely on the first non-exited thread TPID when reading Linux procfs files

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

On 03/09/2026 23:56, Matthieu Longo wrote:
> On 24/08/2026 17:21, Matthieu Longo wrote:
>> On Linux, /proc/<pid> is keyed by the thread-group leader PID. When
>> the leader has exited, some /proc/<pid>/... entries become unavailable
>> even though another thread is still alive. This can happen, for instance,
>> when the main thread calls pthread_exit() and another thread continues
>> the execution (existing test: gcore-stale-thread).
>>
>> This causes GDB to fail to read procfs entries such as cmdline, cwd,
>> exe, maps, and smaps when it uses 'current_inferior ()->pid' after the
>> thread-group leader has exited.
>>
>> Fix this by adding inferior::first_non_exited_thread(), which returns
>> the PTID of the first non-exited thread of the inferior. Use its LWP ID
>> when accessing procfs entries that only need a representative live LWP
>> belonging to the process.
>>
>> This is a best-effort choice of a thread that is expected to still exist
>> in the target. Since GDB's view of the threads list may be stale, the
>> selected thread may already have exited by the time it is accessed.
>> Callers must therefore still be prepared to handle that case.
>>
>> Update the following functions:
>>  - linux_info_proc
>>  - linux_process_address_in_memtag_page
>>  - linux_find_memory_regions_full
>>  - linux_fill_prpsinfo
>>  - linux_address_in_shadow_stack_mem_range
>> to use the first non-exited thread's LWP ID instead of the inferior PID
>> when constructing procfs paths.
>>
>> Add a new test in gdb.threads.
>>
>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31207
>>
>> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
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