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Bug 1642516 - In the Lul stack walker, don't subtract 1 byte from the return address, for consistency with other stackwalkers. r=gerald

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This makes all our stackwalkers in Firefox consistent with respect to return addresses:
For non-leaf frames in stacks, the code address now always points to the instruction
*after* the call instruction, i.e. to the instruction that will be executed once the
function returns.
For symbolication purposes, 1 byte will need to be subtracted in order to obtain correct
line number + inline stack information for  the call instruction. This subtraction will
be the responsibility of the Firefox profiler front-end, not of the stackwalkers.

Depends on D121930

Differential Revision: https://phabricator.services.mozilla.com/D121931
This commit is contained in:
Markus Stange 2021-08-07 00:34:41 +00:00
parent 3077dbd403
commit 06efd253f5
1 changed files with 1 additions and 4 deletions
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5
tools/profiler/lul/LulMain.cpp
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@ -1422,10 +1422,7 @@ void LUL::Unwind(/*OUT*/ uintptr_t* aFramePCs,
}
}
// For the innermost frame, the IA value is what we need. For all
// other frames, it's actually the return address, so back up one
// byte so as to get it into the calling instruction.
aFramePCs[*aFramesUsed] = ia.Value() - (*aFramesUsed == 0 ? 0 : 1);
aFramePCs[*aFramesUsed] = ia.Value();
aFrameSPs[*aFramesUsed] = sp.Valid() ? sp.Value() : 0;
(*aFramesUsed)++;