Comment #6 on issue 2628 by [email protected]:
cctest/test-cpu-profiler/CollectCpuProfile is flaky on Windows
http://code.google.com/p/v8/issues/detail?id=2628
My first hypothesis is:
Imagine the chain of calls A -> B -> C. If we get a sample right at the
start of the code object C when instruction pointer is already pointing to
the callee (C) but frame pointer is still set up for the caller (B) then
stack iterator will think that C's caller is actually A because it'll take
return address based on the frame pointer.
The hypothesis seems to be confirmed. I added the following debug print
(note: for some reason we record code->address() with CodeCreateEvents, not
code->instruction_start() hence the addition of Code::kHeaderSize):
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index e4c750c..12cec1c 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -535,8 +535,17 @@ CodeEntry* CodeMap::FindEntry(Address addr) {
if (tree_.FindGreatestLessThan(addr, &locator)) {
// locator.key() <= addr. Need to check that addr is within entry.
const CodeEntryInfo& entry = locator.value();
- if (addr < (locator.key() + entry.size))
+ if (addr < (locator.key() + entry.size)) {
+ if (addr < locator.key() + Code::kHeaderSize + 4) {
+ PrintF("%s [%p - %p - %p] ~ %p\n",
+ entry.entry->name(),
+ (void*) locator.key(),
+ (void*) (locator.key() + Code::kHeaderSize),
+ (void*) (locator.key() + entry.size),
+ (void*) addr);
+ }
return entry.entry;
+ }
}
return NULL;
}
and got the following with the failure:
loop [0xbeb7c22ce80 - 0xbeb7c22cee0 - 0xbeb7c22d1e4] ~ 0xbeb7c22cee0
[Top down]:
108 0 (root) [-1]
106 0 start [-1]
1 1 loop [-1]
105 6 delay [-1]
99 99 loop [-1]
2 2 (program) [-1]
#
# Fatal error in ../test/cctest/test-cpu-profiler.cc, line 618
# CHECK_EQ(1, startNode->GetChildrenCount()) failed
# Expected: 1
# Found: 2
#
as you can see there was a sample that falls exactly at the code entry
(0xbeb7c22cee0) before the frame pointer (RBP) was updated.
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