On Fri, Sep 16, 2022 at 12:19:36PM +0200, Thomas Neumann via Gcc-patches wrote: > The __register_frame/__deregister_frame functions are used to register > unwinding frames from JITed code in a sorted list. That list itself > is protected by object_mutex, which leads to terrible performance > in multi-threaded code and is somewhat expensive even if single-threaded. > There was already a fast-path that avoided taking the mutex if no > frame was registered at all. > > This commit eliminates both the mutex and the sorted list from > the atomic fast path, and replaces it with a btree that uses > optimistic lock coupling during lookup. This allows for fully parallel > unwinding and is essential to scale exception handling to large > core counts. > > Changes since v3: > - Avoid code duplication by adding query mode to classify_object_over_fdes > - Adjust all comments as requested > > libgcc/ChangeLog: > > * unwind-dw2-fde.c (release_registered_frames): Cleanup at shutdown. > (__register_frame_info_table_bases): Use btree in atomic fast path. > (__deregister_frame_info_bases): Likewise. > (_Unwind_Find_FDE): Likewise. > (base_from_object): Make parameter const. > (classify_object_over_fdes): Add query-only mode. > (get_pc_range): Compute PC range for lookup. > * unwind-dw2-fde.h (last_fde): Make parameter const. > * unwind-dw2-btree.h: New file. > --- > libgcc/unwind-dw2-btree.h | 953 ++++++++++++++++++++++++++++++++++++++ > libgcc/unwind-dw2-fde.c | 195 ++++++-- > libgcc/unwind-dw2-fde.h | 2 +- > 3 files changed, 1098 insertions(+), 52 deletions(-) > create mode 100644 libgcc/unwind-dw2-btree.h >
Hi Thomas, This patch broke avr and pru-elf cross builds: gcc/libgcc/unwind-dw2-fde.c:680:28: error: unknown type name ‘uintptr_t’ 680 | uintptr_t *range) Should uintptr_t be replaced with __UINTPTR_TYPE__? Such change fixes the above broken builds for me. But I'm not sure how valid it is for that part of libgcc. Other embedded targets like arm-none-eabi are not broken because they overwrite LIB2ADDEH, and consequently unwind-dw2-fde.c is not built for them. Regards, Dimitar
