• Stefano Sanfilippo's avatar
    perf jit: Generate .eh_frame/.eh_frame_hdr in DSO · 086f9f3d
    Stefano Sanfilippo authored
    When the jit_buf_desc contains unwinding information, it is emitted as
    eh_frame unwinding sections in the DSOs generated by perf inject.
    
    The unwinding information is required to unwind of JITed code which do
    not maintain the frame pointer register during function calls.  It can
    be emitted by V8 / Chromium when the --perf_prof_unwinding_info is
    passed to V8.
    
    The eh_frame and eh_frame_hdr sections are emitted immediately after the
    .text.
    
    The .eh_frame is aligned at a 8-byte boundary, and .eh_frame_hdr at a
    4-byte one. Since size of the .eh_frame is required to be a multiple of
    the word size, which means there will never be additional padding
    between it and the .eh_frame_hdr on machines where the word size is 4 or
    8 bytes.
    
    However, additional padding might be inserted between .text and
    .eh_frame to reach the correct alignment, which will always be 8 bytes,
    also on 32bit machines. The reasoning behind this choice is that 4 extra
    bytes of padding worst case are not a large cost for the advantage of
    removing word-size dependent offset calculations when emitting the
    jitdump.
    Signed-off-by: default avatarStefano Sanfilippo <ssanfilippo@chromium.org>
    Signed-off-by: default avatarRoss McIlroy <rmcilroy@chromium.org>
    Reviewed-by: default avatarStephane Eranian <eranian@google.com>
    Cc: Anton Blanchard <anton@ozlabs.org>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/1476356383-30100-8-git-send-email-eranian@google.comSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    086f9f3d
genelf.c 11.4 KB