perf/urgent fix

Hi Ingo,

Please consider pulling,

- Arnaldo

The following changes since commit d8a8cfc76919b6c830305266b23ba671623f37ff:

perf/core: Better explain the inherit magic (2017-03-16 14:16:53 +0100)

are available in the git repository at:

git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git tags/perf-urgent-for-mingo-4.11-20170317

for you to fetch changes up to e7ede72a6d40cb3a30c087142d79381ca8a31dab:

perf symbols: Fix symbols__fixup_end heuristic for corner cases (2017-03-17 10:30:22 -0300)

----------------------------------------------------------------
perf/urgent fix

- Fix symbols__fixup_end heuristic for corner cases, such as JITted eBPF programs, that are loaded at page aligned addresses, just after the kernel proper (Daniel Borkmann)

----------------------------------------------------------------
Daniel Borkmann (1):
perf symbols: Fix symbols__fixup_end heuristic for corner cases

 tools/perf/util/symbol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Pulled, thanks Arnaldo!

Ingo

From: Daniel Borkmann <[email protected]>

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.

---
 tools/perf/util/symbol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 70e389bc4af7..9b4d8ba22fed 100644
@@ -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)

2.9.3