| commit | 69359e93face3ea06556fe4d52347fcd08c1b357 | [log] [tgz] |
|---|---|---|
| author | Daniel Cheng <[email protected]> | Thu Jun 20 23:43:02 2019 |
| committer | Commit Bot <[email protected]> | Thu Jun 20 23:43:02 2019 |
| tree | 0494d8b4e872f7c374b0d92c0c8b675339fc60f0 | |
| parent | e495062bb06c8b5b03f4eec0507a097d036e5981 [diff] |
Shorten TRAP_SEQUENCE on Intel.
On Intel, TRAP_SEQUENCE() consisted of:
int3 // Breakpoint
ud2 // Make sure it crashes in case a developer
// steps past the breakpoint
push $<unique value> // Prevent trap sequences from being merged
ud2 // Only on Windows x64 and Mac, quirk of
// __builtin_unreachable().
Previously, the push instruction was required to make CHECKs somewhat
unique, so that compilers like gcc wouldn't fold all the CHECKs in a
function into one common sequence.
However, clang won't fold asm sequences together, so just drop the push
completely.
On Win64 and Mac, also drop the explicit ud2 from TRAP_SEQUENCE:
__builtin_unreachable() always emits a ud2 on those platforms, and
there's no reason to have ud2 twice in a row.
To simplify followups, this CL also temporarily splits the TRAP_SEQUENCE
macro into TRAP_SEQUENCE1 and TRAP_SEQUENCE2:
- TRAP_SEQUENCE1() is responsible for triggering a debug breakpoint.
- TRAP_SEQUENCE2() is responsible for ensuring fatal termination.
Staged followups will turn TRAP_SEQUENCE1 into no-ops. Assuming crash
reports aren't affected, the final followup will remove TRAP_SEQUENCE1
entirely.
Bug: 958675
Change-Id: Id86e70a23a1407404721b9da4f2d2374fa86dc3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1589282
Commit-Queue: Daniel Cheng <[email protected]>
Reviewed-by: Mark Mentovai <[email protected]>
Reviewed-by: Bruce Dawson <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/master@{#671123}
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