On 6/21/22 09:56, Richard Biener wrote:
> On Mon, Jun 20, 2022 at 12:20 PM Martin Liška <mliska@suse.cz> wrote:
>>
>> On 6/20/22 11:32, Richard Biener wrote:
>>> On Thu, Jun 16, 2022 at 9:01 AM Martin Liška <mliska@suse.cz> wrote:
>>>>
>>>> lto-plugin/ChangeLog:
>>>>
>>>>         * lto-plugin.c (plugin_lock): New lock.
>>>>         (claim_file_handler): Use mutex for critical section.
>>>>         (onload): Initialize mutex.
>>>> ---
>>>>  lto-plugin/lto-plugin.c | 16 +++++++++++++++-
>>>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lto-plugin/lto-plugin.c b/lto-plugin/lto-plugin.c
>>>> index 00b760636dc..13118c4983c 100644
>>>> --- a/lto-plugin/lto-plugin.c
>>>> +++ b/lto-plugin/lto-plugin.c
>>>> @@ -55,6 +55,7 @@ along with this program; see the file COPYING3.  If not see
>>>>  #include <unistd.h>
>>>>  #include <fcntl.h>
>>>>  #include <sys/types.h>
>>>> +#include <pthread.h>
>>>
>>> Not sure if we support any non-pthread target for building the LTO
>>> plugin, but it
>>> seems we have
>>>
>>>   # Among non-ELF, only Windows platforms support the lto-plugin so far.
>>>   # Build it unless LTO was explicitly disabled.
>>>   case $target in
>>>     *-cygwin* | *-mingw*) build_lto_plugin=$enable_lto ;;
>>>
>>> which suggests that at least build validating the above with --enable-lto
>>
>> Verified that it's fine.
>>
>>>
>>> IIRC we have gthr-*.h in libgcc/, not sure if that's usable in a
>>> host linker plugin.
>>>
>>>>  #ifdef HAVE_SYS_WAIT_H
>>>>  #include <sys/wait.h>
>>>>  #endif
>>>> @@ -157,6 +158,9 @@ enum symbol_style
>>>>    ss_uscore,   /* Underscore prefix all symbols.  */
>>>>  };
>>>>
>>>> +/* Plug-in mutex.  */
>>>> +static pthread_mutex_t plugin_lock;
>>>> +
>>>>  static char *arguments_file_name;
>>>>  static ld_plugin_register_claim_file register_claim_file;
>>>>  static ld_plugin_register_all_symbols_read register_all_symbols_read;
>>>> @@ -1262,15 +1266,18 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
>>>>                               lto_file.symtab.syms);
>>>>        check (status == LDPS_OK, LDPL_FATAL, "could not add symbols");
>>>>
>>>> +      pthread_mutex_lock (&plugin_lock);
>>>>        num_claimed_files++;
>>>>        claimed_files =
>>>>         xrealloc (claimed_files,
>>>>                   num_claimed_files * sizeof (struct plugin_file_info));
>>>>        claimed_files[num_claimed_files - 1] = lto_file;
>>>> +      pthread_mutex_unlock (&plugin_lock);
>>>>
>>>>        *claimed = 1;
>>>>      }
>>>>
>>>> +  pthread_mutex_lock (&plugin_lock);
>>>>    if (offload_files == NULL)
>>>>      {
>>>>        /* Add dummy item to the start of the list.  */
>>>> @@ -1333,11 +1340,12 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
>>>>         offload_files_last_lto = ofld;
>>>>        num_offload_files++;
>>>>      }
>>>> +  pthread_mutex_unlock (&plugin_lock);
>>>>
>>>>    goto cleanup;
>>>>
>>>>   err:
>>>> -  non_claimed_files++;
>>>> +  __atomic_fetch_add (&non_claimed_files, 1, __ATOMIC_RELAXED);
>>>
>>> is it worth "optimizing" this with yet another need for target specific support
>>> (just use pthread_mutex here as well?)
>>
>> Sure.
>>
>> May I install the patch with the change?
> 
> Can you at least add a configure check for pthread.h and maybe disable
> locking when not found or erroring out?  I figure we have GCC_AC_THREAD_HEADER

All right, let's error out then.

> for the gthr.h stuff using $target_thread_file (aka --enable-threads=XYZ),
> but as said that's for the target and I don't see any host uses.  We might also
> add an explicit list of hosts (*-linux*?) where we enable thread support for
> lto-plugin, providing opt-in (so you'd have to wrap the mutex taking or
> if-def it out).
> 
> I think you also need to link lto-plugin with -pthread, no?

Yep.

Please see the updated patch.

> On linux
> it might work omitting that but I'm not sure other libc have serial pthread
> stubs in their libc.  BFD ld definitely doesn't link against pthread so
> dlopening lto-plugin will fail (also not all libc might like
> initializing threads
> from a dlopen _init).

What initializing threads do you mean?

Martin

> 
> Richard.
> 
>> Cheers,
>> Martin
>>
>>>
>>>>    free (lto_file.name);
>>>>
>>>>   cleanup:
>>>> @@ -1415,6 +1423,12 @@ onload (struct ld_plugin_tv *tv)
>>>>    struct ld_plugin_tv *p;
>>>>    enum ld_plugin_status status;
>>>>
>>>> +  if (pthread_mutex_init (&plugin_lock, NULL) != 0)
>>>> +    {
>>>> +      fprintf (stderr, "mutex init failed\n");
>>>> +      abort ();
>>>> +    }
>>>> +
>>>>    p = tv;
>>>>    while (p->tv_tag)
>>>>      {
>>>> --
>>>> 2.36.1
>>>>
>>>>