perf jit: Add unwinding support

This record is intended to provide unwinding information in the
eh_frame format. This is required to unwind JITed code which
does not maintain the frame pointer register during function calls.

The eh_frame unwinding information can be emitted by V8 / Chromium
when the --perf_prof_unwinding_info is passed.

A record of type jr_code_unwinding_info comes before the jr_code_load
it referred to and contains both the .eh_frame and .eh_frame_hdr.

The fields in the header have the following meaning:

  * unwinding_size: size of the eh_frame and eh_frame_hdr, necessary
    for distinguishing the content from the padding.

  * eh_frame_hdr_size: as the name says.

  * mapped_size: size of the payload that was in memory at runtime.
    typically unwinding_size if the .eh_frame_hdr and .eh_frame were
    mapped, or 0 if they weren't. It should always be the former case,
    since the .eh_frame is guaranteed to be mapped in memory. However,
    certain JITs might want to inject an .eh_frame_hdr with an empty LUT
    to trigger fp-based unwinding fallback in libunwind. The only part
    of the .eh_frame_hdr that libunwind reads from remote memory is the
    LUT, and since there is none, mapping the unwinding info in memory
    is not necessary, and 0 in this field signifies that it wasn't.
    This practical hack allows to save bytes in code memory for those
    JIT compilers that might or might not maintain a valid frame pointer.

The payload that follows is assumed to contain first the .eh_frame and
then the .eh_header_hdr, with no padding between the two.

Signed-off-by: Stefano Sanfilippo <ssanfilippo@chromium.org>
Signed-off-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Stephane 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/1476356383-30100-7-git-send-email-eranian@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/tools/perf/util/jitdump.h b/tools/perf/util/jitdump.h
index bcacd20d0c1c..c6b9b67f43bf 100644
--- a/tools/perf/util/jitdump.h
+++ b/tools/perf/util/jitdump.h
@@ -19,6 +19,7 @@
 #define JITHEADER_MAGIC_SW	0x4454694A
 
 #define PADDING_8ALIGNED(x) ((((x) + 7) & 7) ^ 7)
+#define ALIGN_8(x) (((x) + 7) & (~7))
 
 #define JITHEADER_VERSION 1
 
@@ -48,6 +49,7 @@ enum jit_record_type {
         JIT_CODE_MOVE           = 1,
 	JIT_CODE_DEBUG_INFO	= 2,
 	JIT_CODE_CLOSE		= 3,
+	JIT_CODE_UNWINDING_INFO	= 4,
 
 	JIT_CODE_MAX,
 };
@@ -101,12 +103,22 @@ struct jr_code_debug_info {
 	struct debug_entry entries[0];
 };
 
+struct jr_code_unwinding_info {
+	struct jr_prefix p;
+
+	uint64_t unwinding_size;
+	uint64_t eh_frame_hdr_size;
+	uint64_t mapped_size;
+	const char unwinding_data[0];
+};
+
 union jr_entry {
         struct jr_code_debug_info info;
         struct jr_code_close close;
         struct jr_code_load load;
         struct jr_code_move move;
         struct jr_prefix prefix;
+        struct jr_code_unwinding_info unwinding;
 };
 
 static inline struct debug_entry *