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[vm] Update workaround for Android Kernel bug (b089d4f).

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Previous workaround was only compilable by GCC - new one is compilable
with both but is less robust because theoretically compiler can simply
use registers r0-r2 as temporaries whenever it desires.

Bug: https://github.com/flutter/flutter/issues/22172

Change-Id: Ic73fde8d3342c1455ab01ed8b7d4b267aebda136
Reviewed-on: https://dart-review.googlesource.com/76021
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
This commit is contained in:
Vyacheslav Egorov 2018-09-24 20:16:08 +00:00 committed by commit-bot@chromium.org
parent ef7d144bc7
commit e9586a5d14
1 changed files with 15 additions and 8 deletions
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23
runtime/vm/signal_handler.h
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@ -94,19 +94,26 @@ class SignalHandler : public AllStatic {
void* context_) {
// IT (If-Then) instruction makes up to four instructions that follow it
// conditional.
asm volatile("nop; nop; nop; nop" : : : "memory");
// Note: clobber all register so that compiler does not attempt to hoist
// anything from the next assembly block past this one.
asm volatile("nop; nop; nop; nop;"
:
:
: "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
"r10", "r11", "r12", "r13", "r14", "memory");
// Tail-call into the actual signal handler.
//
// Note: this code is split into a separate inline assembly block because
// any code that compiler generates to satisfy register constraints must
// be generated after four NOPs.
register int arg0 asm("r0") = signal;
register siginfo_t* arg1 asm("r1") = info;
register void* arg2 asm("r2") = context_;
asm volatile("bx %3"
:
: "r"(arg0), "r"(arg1), "r"(arg2), "r"(action)
: "memory");
//
// Note: there is no portable way to specify that we want to have
// signal, info and context_ in r0 - r2 respectively. So we just mark them
// as clobbered and hope that compiler does not emit any code that uses
// these registers to satisfy action constraint (we tested on clang and
// the generated code looks like one would expect).
asm volatile("bx %0;" : : "r"(action) : "r0", "r1", "r2", "memory");
}
#endif // defined(USE_SIGNAL_HANDLER_TRAMPOLINE)
};