-C panic=abort doesn't generate EHABI information on arm #49867
Comments
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Note the same actually applies to EH_FRAME info on x86-64, which iirc the Firefox profiler also uses on x86-64. More generally, it can be desirable to have unwind info even when panic doesn't unwind. |
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For C/C++ code in Firefox we use The equivalent for x86-64 is It seems like having a compiler option to enable this would be good enough, since the behavior here mirrors what gcc does: only emit unwind info if needed for exceptions/unwinding. |
pietroalbini
added
C-enhancement
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LLVM seems to turn on EHABI as default by https://reviews.llvm.org/D2627 (EnableARMEHABI is removed by this landing, but src/rustllvm/PassWrapper.cpp still has it) |
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This may or may not be related to #45031, but I can prepare a patch like #40549 for the targets here. @makotokato do you know what targets are in use by Firefox and would need this treatment? |
Long ago (rust-lang#40549) we enabled the `uwtable` attribute on Windows by default (even with `-C panic=abort`) to allow unwinding binaries for [stack unwinding information][winstack]. It looks like this same issue is [plaguing][arm1] Gecko's Android platforms [as well][arm2]. This commit applies the same fix as rust-lang#40549 except that this time it's applied for all Android targets. Generating a `-C panic=abort` binary for `armv7-linux-androideabi` before this commit generated a number of `cantunwind` functions (detected with `readelf -u`) but after this commit they all list appropriate unwind information. Closes rust-lang#49867 [winstack]: https://bugzilla.mozilla.org/show_bug.cgi?id=1302078 [arm1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1453220 [arm2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1451741
rustc: Always emit `uwtable` on Android Long ago (#40549) we enabled the `uwtable` attribute on Windows by default (even with `-C panic=abort`) to allow unwinding binaries for [stack unwinding information][winstack]. It looks like this same issue is [plaguing][arm1] Gecko's Android platforms [as well][arm2]. This commit applies the same fix as #40549 except that this time it's applied for all Android targets. Generating a `-C panic=abort` binary for `armv7-linux-androideabi` before this commit generated a number of `cantunwind` functions (detected with `readelf -u`) but after this commit they all list appropriate unwind information. Closes #49867 [winstack]: https://bugzilla.mozilla.org/show_bug.cgi?id=1302078 [arm1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1453220 [arm2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1451741
ghost
mentioned this issue
Allow not emitting `uwtable` on Android `uwtable` is marked as required on Android, so it can't be disabled via `-C force-unwind-tables=no`. However, I found that the reason it's marked as required was to resolve a [backtrace issue in Gecko](rust-lang#49867), and I haven't find any other reasons that make it required ([yet](https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/Unwind.20tables.20are.20strictly.20required.20on.20Windows.20and.20Android)). Therefore, I assume it's safe to turn it off if a (nice) backtrace is not needed, and submit this PR to allow `-C force-unwind-tables=no` when targeting Android. Note that I haven't tested this change on Android as I don't have an Android environment for testing.
From https://bugzilla.mozilla.org/show_bug.cgi?id=1453220
Gecko profiler uses EHABI information to walk stack. But since rustc doesn't generate EHABI, it cannot walk stack on generated code by rust.
@glandium says, "-C panic=abort" causes that EHABI isn't emitted", so we need a option not to remove it (or don't remove EHABI even if -C panic=abort).
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