8000 Better SEGV handling by NickBarnes · Pull Request #4061 · oxcaml/oxcaml · GitHub
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Better SEGV handling #4061

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Better SEGV handling #4061

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44 changes: 33 additions & 11 deletions runtime/signals_nat.c
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Original file line number Diff line number Diff line change
Expand Up @@ -96,43 +96,65 @@ void caml_garbage_collection(void)
#error "stack checks cannot be disabled if POSIX signals are not available"
#endif

typedef void (*sigaction_t)(int sig, siginfo_t *info, void *context);

#define DECLARE_SIGNAL_HANDLER(name) \
static void name(int sig, siginfo_t * info, ucontext_t * context)

#define SET_SIGACT(sigact,name) \
sigact.sa_sigaction = (void (*)(int,siginfo_t *,void *)) (name); \
sigact.sa_sigaction = (sigaction_t) (name); \
sigact.sa_flags = SA_SIGINFO

CAMLextern void caml_raise_stack_overflow_nat(void);

static sigaction_t prior_segv_handler = NULL;

DECLARE_SIGNAL_HANDLER(segv_handler)
{
struct sigaction act;
struct stack_info *block = Caml_state->current_stack;
char* fault_addr = info->si_addr;
char* protected_low = Protected_stack_page(block);
char* protected_high = protected_low + caml_plat_pagesize;
if ((fault_addr >= protected_low) && (fault_addr < protected_high)) {
if (Caml_state) {
struct stack_info *block = Caml_state->current_stack;
char* fault_addr = info->si_addr;
char* protected_low = Protected_stack_page(block);
char* protected_high = protected_low + caml_plat_pagesize;
if ((fault_addr >= protected_low) && (fault_addr < protected_high)) {
/* Faulting in the current guard page; presume stack overflow. Raise the
exception. */
#ifdef SYS_macosx
context->uc_mcontext->__ss.__rip = (unsigned long long) &caml_raise_stack_overflow_nat;
context->uc_mcontext->__ss.__rip = (unsigned long long) &caml_raise_stack_overflow_nat;
#else
context->uc_mcontext.gregs[REG_RIP]= (greg_t) &caml_raise_stack_overflow_nat;
context->uc_mcontext.gregs[REG_RIP]= (greg_t) &caml_raise_stack_overflow_nat;
#endif
} else {
return; /* to caml_raise_stack_overflow_nat */
}
}

/* Not a stack-overflow on our current Caml stack */
if (prior_segv_handler) {
/* Somebody else installed a SEGV handler before us. We make
* "reasonable best efforts" to invoke it, as maybe it's a SEGV
* they know about and can fix. We can't apply whatever sa_flags
* they had, but we can call their handler. */
prior_segv_handler(sig, info, context);
} else { /* default SEGV behaviour */
act.sa_handler = SIG_DFL;
act.sa_flags = 0;
sigemptyset(&act.sa_mask);
sigaction(SIGSEGV, &act, NULL);
}
/* returning from SEGV handler restarts the failing instruction */
}

void caml_init_nat_signals(void)
{
struct sigaction act;
struct sigaction act, oldact;
SET_SIGACT(act, segv_handler);
act.sa_flags |= SA_ONSTACK | SA_NODEFER;
sigemptyset(&act.sa_mask);
sigaction(SIGSEGV, &act, NULL);
sigaction(SIGSEGV, &act, &oldact);
if (oldact.sa_sigaction != (sigaction_t)SIG_DFL) {
prior_segv_handler = oldact.sa_sigaction;
}
}

#else
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