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#include "types.hh"
#include <cstring>
#include <cstddef>
#include <cstdlib>
#include <unistd.h>
#include <signal.h>
namespace nix {
static void sigsegvHandler(int signo, siginfo_t * info, void * ctx)
{
/* Detect stack overflows by comparing the faulting address with
the stack pointer. Unfortunately, getting the stack pointer is
not portable. */
bool haveSP = true;
char * sp = 0;
#if defined(__x86_64__) && defined(REG_RSP)
sp = (char *) ((ucontext_t *) ctx)->uc_mcontext.gregs[REG_RSP];
#elif defined(REG_ESP)
sp = (char *) ((ucontext_t *) ctx)->uc_mcontext.gregs[REG_ESP];
#else
haveSP = false;
#endif
if (haveSP) {
ptrdiff_t diff = (char *) info->si_addr - sp;
if (diff < 0) diff = -diff;
if (diff < 4096) {
char msg[] = "error: stack overflow (possible infinite recursion)\n";
[[gnu::unused]] auto res = write(2, msg, strlen(msg));
_exit(1); // maybe abort instead?
}
}
/* Restore default behaviour (i.e. segfault and dump core). */
struct sigaction act;
sigfillset(&act.sa_mask);
act.sa_handler = SIG_DFL;
act.sa_flags = 0;
if (sigaction(SIGSEGV, &act, 0)) abort();
}
void detectStackOverflow()
{
#if defined(SA_SIGINFO) && defined (SA_ONSTACK)
/* Install a SIGSEGV handler to detect stack overflows. This
requires an alternative stack, otherwise the signal cannot be
delivered when we're out of stack space. */
stack_t stack;
stack.ss_size = 4096 * 4 + MINSIGSTKSZ;
static auto stackBuf = std::make_unique<std::vector<char>>(stack.ss_size);
stack.ss_sp = stackBuf->data();
if (!stack.ss_sp) throw Error("cannot allocate alternative stack");
stack.ss_flags = 0;
if (sigaltstack(&stack, 0) == -1) throw SysError("cannot set alternative stack");
struct sigaction act;
sigfillset(&act.sa_mask);
act.sa_sigaction = sigsegvHandler;
act.sa_flags = SA_SIGINFO | SA_ONSTACK;
if (sigaction(SIGSEGV, &act, 0))
throw SysError("resetting SIGSEGV");
#endif
}
}
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