Re: [Valgrind-developers] [valgrind] coregrind/m_debuginfo: don't try to examine zero sized mmapped files

[ISHIKAWA,chiaki <ish...@yk...>]

Dear Mark,

It works.
I don't get the noisy warnings any more.

Thank you for the quick fix!

Chiaki


On 2025/03/10 14:43, ISHIKAWA,chiaki wrote:
> Dear Mark,
>
> Thank you for your analysis.
>
> I will try to create a localized version of valgrind after applying 
> the patch and see how it goes.
>
> It might take a couple of days due to my day job, etc.
>
> Chiaki
>
> On 2025/03/10 5:45, Mark Wielaard wrote:
>> Hi Chiaki,
>>
>> On Mon, Mar 10, 2025 at 03:32:16AM +0900, ISHIKAWA,chiaki wrote:
>>> Does this help reduce the occurences of presumably non-critical
>>> error messages like the following?
>> No. These are indeed related messages, but caused by using memfd
>> allocated memory.
>>
>>> I get this when I try to run mozilla's thunderbird mail client under
>>> valgrind.
>>> They appear many times.
>>>
>>>    23:44.69 GECKO(2640779) --2640783-- WARNING: Serious error when
>>> reading debug info
>>>    23:44.69 GECKO(2640779) --2640783-- When reading debug info from
>>> /memfd:mozilla-ipc (deleted):
>>>    23:44.69 GECKO(2640779) --2640783-- failed to stat64/stat this file
>>>    23:44.69 GECKO(2640779) --2640783-- WARNING: Serious error when
>>> reading debug info
>>>    23:44.69 GECKO(2640779) --2640783-- When reading debug info from
>>> /memfd:mozilla-ipc (deleted):
>>>    23:44.69 GECKO(2640779) --2640783-- failed to stat64/stat this file
>>>
>>> I have no idea why valgrind wants try to to read debug info from
>>> memory region.
>> I presume because valgrind thinks it might be a real memory mapped
>> file. The code triggering this warning is:
>>
>>     /* Don't let the stat call fail silently.  Filter out some known
>>        sources of noise before complaining, though. */
>>     if (sr_isError(statres)) {
>>        DebugInfo fake_di;
>>        Bool quiet = VG_(strstr)(filename, "/var/run/nscd/") != NULL
>>                     || VG_(strstr)(filename, "/dev/shm/") != NULL;
>>        if (!quiet && VG_(clo_verbosity) > 1) {
>>           VG_(memset)(&fake_di, 0, sizeof(fake_di));
>>           fake_di.fsm.filename = 
>> ML_(dinfo_strdup)("di.debuginfo.nmm", filename);
>>           ML_(symerr)(&fake_di, True, "failed to stat64/stat this 
>> file");
>>        }
>>        return 0;
>>     }
>>
>> So we probably should add "/memfd:" to the patterns for which not to
>> warn.
>>
>> https://www.man7.org/linux/man-pages/man2/memfd_create.2.html says:
>>
>>         int memfd_create(const char *name, unsigned int flags);
>>
>>      The name supplied in name is used as a filename and will be
>>      displayed as the target of the corresponding symbolic link in the
>>      directory /proc/self/fd/.  The displayed name is always prefixed
>>      with memfd: and serves only for debugging purposes.
>>
>> So I would propose something like the following (untested) patch:
>>
>> diff --git a/coregrind/m_debuginfo/debuginfo.c 
>> b/coregrind/m_debuginfo/debuginfo.c
>> index 15686fc5c46f..6c4a6926560b 100644
>> --- a/coregrind/m_debuginfo/debuginfo.c
>> +++ b/coregrind/m_debuginfo/debuginfo.c
>> @@ -1196,7 +1196,9 @@ ULong VG_(di_notify_mmap)( Addr a, Bool 
>> allow_SkFileV, Int use_fd )
>>      if (sr_isError(statres)) {
>>         DebugInfo fake_di;
>>         Bool quiet = VG_(strstr)(filename, "/var/run/nscd/") != NULL
>> -                   || VG_(strstr)(filename, "/dev/shm/") != NULL;
>> +                   || VG_(strstr)(filename, "/dev/shm/") != NULL
>> +                   || VG_(strncmp)("/memfd:", filename,
>> +                                   VG_(strlen)("/memfd:")) == 0;
>>         if (!quiet && VG_(clo_verbosity) > 1) {
>>            VG_(memset)(&fake_di, 0, sizeof(fake_di));
>>            fake_di.fsm.filename = 
>> ML_(dinfo_strdup)("di.debuginfo.nmm", filename);
>>
>> Does that work for you?
>>
>> Thanks,
>>
>> Mark
>
>
>
>
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