From: Daniel Borkmann daniel@iogearbox.net
[ Upstream commit e7ede72a6d40cb3a30c087142d79381ca8a31dab ]
The current symbols__fixup_end() heuristic for the last entry in the rb tree is suboptimal as it leads to not being able to recognize the symbol in the call graph in a couple of corner cases, for example:
i) If the symbol has a start address (f.e. exposed via kallsyms) that is at a page boundary, then the roundup(curr->start, 4096) for the last entry will result in curr->start == curr->end with a symbol length of zero.
ii) If the symbol has a start address that is shortly before a page boundary, then also here, curr->end - curr->start will just be very few bytes, where it's unrealistic that we could perform a match against.
Instead, change the heuristic to roundup(curr->start, 4096) + 4096, so that we can catch such corner cases and have a better chance to find that specific symbol. It's still just best effort as the real end of the symbol is unknown to us (and could even be at a larger offset than the current range), but better than the current situation.
Alexei reported that he recently run into case i) with a JITed eBPF program (these are all page aligned) as the last symbol which wasn't properly shown in the call graph (while other eBPF program symbols in the rb tree were displayed correctly). Since this is a generic issue, lets try to improve the heuristic a bit.
Reported-and-Tested-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Fixes: 2e538c4a1847 ("perf tools: Improve kernel/modules symbol lookup") Link: http://lkml.kernel.org/r/bb5c80d27743be6f12afc68405f1956a330e1bc9.1489614365... Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin alexander.levin@verizon.com --- tools/perf/util/symbol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index f7b35e178582..f199d5b11d76 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -202,7 +202,7 @@ void symbols__fixup_end(struct rb_root *symbols)
/* Last entry */ if (curr->end == curr->start) - curr->end = roundup(curr->start, 4096); + curr->end = roundup(curr->start, 4096) + 4096; }
void __map_groups__fixup_end(struct map_groups *mg, enum map_type type)