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SubjectRe: [PATCH 2/2] perf unwind: fix libunwind when tid != pid
On Mon, Jul 29, 2019 at 06:24:30PM +0100, John Keeping wrote:
> Commit e5adfc3e7e77 ("perf map: Synthesize maps only for thread group
> leader") changed the recording side so that we no longer get mmap events
> for threads other than the thread group leader.
>
> When a file recorded after this change is loaded, the lack of mmap
> records mean that unwinding is not set up for any other threads.

sry I dont' follow what's the problem here, could you please
describe the scenrio where the current code is failing in
more details

>
> Following the rationale in that commit, move the libunwind fields into
> struct map_groups and update the libunwind functions to take this
> instead of the struct thread. This is only required for
> unwind__finish_access which must now be called from map_groups__delete
> and the others are changed for symmetry.
>
> Note that unwind__get_entries keeps the thread argument since it is
> required for symbol lookup and the libdw unwind provider uses the thread
> ID.

SNIP

> @@ -59,37 +59,31 @@ int unwind__prepare_access(struct thread *thread, struct map *map,
> return 0;
> }
> out_register:
> - unwind__register_ops(thread, ops);
> + unwind__register_ops(mg, ops);
>
> - err = thread->unwind_libunwind_ops->prepare_access(thread);
> + err = mg->unwind_libunwind_ops->prepare_access(mg);
> if (initialized)
> *initialized = err ? false : true;
> return err;
> }
>
> -void unwind__flush_access(struct thread *thread)
> +void unwind__flush_access(struct map_groups *mg)
> {
> - if (!dwarf_callchain_users)
> - return;

why did you remove this check?

> -
> - if (thread->unwind_libunwind_ops)
> - thread->unwind_libunwind_ops->flush_access(thread);
> + if (mg->unwind_libunwind_ops)
> + mg->unwind_libunwind_ops->flush_access(mg);
> }
>
> -void unwind__finish_access(struct thread *thread)
> +void unwind__finish_access(struct map_groups *mg)
> {
> - if (!dwarf_callchain_users)
> - return;

why did you remove this check?

thanks,
jirka

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