Use C++ to JIT entry registers on Win/x64 to resume stack walking when lost
Categories
(Core :: Gecko Profiler, task, P2)
Tracking
()
| Tracking | Status | |
|---|---|---|
| firefox91 | --- | fixed |
People
(Reporter: mozbugz, Assigned: mozbugz)
References
(Depends on 1 open bug)
Details
Attachments
(4 files, 3 obsolete files)
From bug 1700869, JS::ProfilingFrameIterator::getCppEntryRegisters() can give us the appropriate register values that can be used to resume stack walking if it gets lost in JIT code.
This bug/task will build the foundations for this, and focus on the Windows x86-64 implementation. More platforms will be added in later bugs.
|
Assignee | |
Comment 1•3 years ago
|
||
Since mozglue doesn't know about JIT, this is a generic control structures that will only deal with the few registers needed to stop and resume stack-walking.
|
|
Assignee | |
Comment 2•3 years ago
|
||
On platforms like Windows, we will need PC and SP, but also BP. To avoid polluting common functions with this unneeded information, the new StackWalkControl will record it before the callback is invoked.
StackWalkControl also contains "ResumePoint"s, with the following information:
- Where to stop stack-walking (this will be used to avoid unnecessarily walking JIT code native frames),
- Where to resume (if stopped, or if the walker gets lost),
- Whether to output stop/resume frames.
Depends on D113269
|
|
Assignee | |
Comment 3•3 years ago
|
||
DoMozStackWalkThread is the main stack walker for Windows.
Note that since StackWalkControl is only implemented for x86-64, so this patch effectively only applies to that platform (for now).
Depends on D113270
|
|
Assignee | |
Comment 4•3 years ago
|
||
This is almost code-free: An empty StackWalkControl is constructed where&when needed, and then passed to ExtractJsFrames and the stack walker, but is not actively used yet.
(See next patch for ExtractJsFrames implementation.)
Depends on D113271
|
|
Assignee | |
Comment 5•3 years ago
|
||
ExtractJsFrames should now fill the provided StackWalkControl with C++-to-JIT entry registers, if any.
This patch connects the JIT data to StackWalkControl and MozStackWalkThread that have been implemented on Windows/x86-64 in previous patches. So on this platform, profile should now contain fewer incomplete stacks.
Depends on D113272
|
|
Assignee | |
Comment 6•3 years ago
•
|
||
Startup+reddit profile before: https://share.firefox.dev/3xligsy
Startup+reddit profile with patches: https://share.firefox.dev/2QvcILv
The main difference to notice is the number of incomplete stacks, which is visible in the Call Tree, with stacks starting with a label like "XREMain::XRE_main" or "XRE_InitChildProcess", instead of a native function like RtlUserThreadStart.
For example, looking at "Web Content (3/3)" which handled Reddit, the number of incomplete stacks went from 44% down to 6.3%. And in the parent process, 12% to 0.7%. 😄🎉
It's also noticeable more visually in the Stack Chart, where frames near the root now form longer uninterrupted blocks, with more of the native gray frames.
|
|
Assignee | |
Comment 7•3 years ago
|
||
Let's wait for bug 1712674 to be resolved (as it's a simpler fix for most bad-stack issues), before coming back here...
|
||
Updated•3 years ago
|
|
|
||
Updated•3 years ago
|
|
|
||
Updated•3 years ago
|
|
|
Assignee | |
Comment 8•3 years ago
|
||
This structure manages a list of known "ResumePoint", which contains the registers needed to restart stack walks from JIT C++ entry points.
Depends on D113272
|
|
Assignee | |
Comment 9•3 years ago
|
||
When mozglue's MozStackWalkThread ends, the last found SP can be checked to see if it was called by JIT code, in which case we can restart the native stack walk from the known caller of the JIT code.
Depends on D113273
|
||
Comment 10•3 years ago
|
||
Pushed by gsquelart@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/5fb8ebb1a365 Pass StackWalkControl to ExtractJsFrames and then forward it to stack walkers - r=canaltinova https://hg.mozilla.org/integration/autoland/rev/e582c06a7323 Implement StackWalkControl struct on Windows/x86-64 - r=canaltinova https://hg.mozilla.org/integration/autoland/rev/a5c3c4a00acc Retrieve entry registers and stop areas from JIT - r=canaltinova https://hg.mozilla.org/integration/autoland/rev/92276cf98902 Use StackWalkControl in Profiler's DoMozStackWalkBacktrace - r=canaltinova
|
||
Comment 11•3 years ago
|
||
Backed out for causing build bustages. The build bustages are happening on Windows 2012 AArch64 opt and debug.
|
|
Assignee | |
Comment 12•3 years ago
|
||
Thank you.
Using #error in the false branch of if constexpr (StackWalkControl::scIsSupported) was wrong, as the preprocessor #error is not suppressed as I may have thought. I'll fix and re-test before landing...
|
|
||
Comment 13•3 years ago
|
||
Pushed by gsquelart@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/b8d18e3e34c1 Pass StackWalkControl to ExtractJsFrames and then forward it to stack walkers - r=canaltinova https://hg.mozilla.org/integration/autoland/rev/5eebaf1cdc31 Implement StackWalkControl struct on Windows/x86-64 - r=canaltinova https://hg.mozilla.org/integration/autoland/rev/750af5adba75 Retrieve entry registers and stop areas from JIT - r=canaltinova https://hg.mozilla.org/integration/autoland/rev/d93c8ecddf48 Use StackWalkControl in Profiler's DoMozStackWalkBacktrace - r=canaltinova
|
||
Comment 14•3 years ago
|
||
| bugherder | ||
https://hg.mozilla.org/mozilla-central/rev/b8d18e3e34c1
https://hg.mozilla.org/mozilla-central/rev/5eebaf1cdc31
https://hg.mozilla.org/mozilla-central/rev/750af5adba75
https://hg.mozilla.org/mozilla-central/rev/d93c8ecddf48
Description
•