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Ignore SEGV during profiler unwind on Unix #28291

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merged 3 commits into from
Jul 30, 2018
Merged

Ignore SEGV during profiler unwind on Unix #28291

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5730dc0
Ignore SEGV during profiler unwind on Unix.
maleadt Jul 26, 2018
24413c6
Alternative approach based on setjmp/longjmp with ptls->safe_restore.
maleadt Jul 26, 2018
a526b29
Reuse jl_call_in_ctx.
maleadt Jul 27, 2018
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21 changes: 18 additions & 3 deletions src/signals-unix.c
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Original file line number Diff line number Diff line change
Expand Up @@ -220,11 +220,19 @@ static int jl_is_on_sigstack(jl_ptls_t ptls, void *ptr, void *context)
is_addr_on_sigstack(ptls, (void*)jl_get_rsp_from_ctx(context)));
}

volatile static int profiler_state = 0;
static ucontext_t profiler_uc;

static void segv_handler(int sig, siginfo_t *info, void *context)
{
jl_ptls_t ptls = jl_get_ptls_states();
assert(sig == SIGSEGV || sig == SIGBUS);

if (profiler_state == 1) {
profiler_state = 2;
setcontext(&profiler_uc);
}

if (jl_addr_is_safepoint((uintptr_t)info->si_addr)) {
#ifdef JULIA_ENABLE_THREADING
jl_set_gc_and_wait();
Expand Down Expand Up @@ -667,9 +675,16 @@ static void *signal_listener(void *arg)
// do backtrace for profiler
if (profile && running) {
if (bt_size_cur < bt_size_max - 1) {
// Get backtrace data
bt_size_cur += rec_backtrace_ctx((uintptr_t*)bt_data_prof + bt_size_cur,
bt_size_max - bt_size_cur - 1, signal_context);
profiler_state = 1;
getcontext(&profiler_uc);
if (profiler_state == 1) {
// Get backtrace data
bt_size_cur += rec_backtrace_ctx((uintptr_t*)bt_data_prof + bt_size_cur,
bt_size_max - bt_size_cur - 1, signal_context);
} else {
jl_safe_printf("WARNING: profiler attempt to access an invalid memory location\n");
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Is there any risk of printing this message on each profile interval?

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Just mimicking

julia/src/signals-mach.c

Line 468 in 614d917

jl_safe_printf("WARNING: profiler attempt to access an invalid memory location\n");
. I agree it's not an interesting message for users though, but I've only seen it print at most a couple of times during nontrivial (1-10s) profile invocations.

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Ok.

}

// Mark the end of this block with 0
bt_data_prof[bt_size_cur++] = 0;
}
Expand Down