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#include <csignal>
#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <unistd.h>
#include "libutil/types.hh"
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 = nullptr;
#if defined(__x86_64__) && defined(REG_RSP)
sp = (char*)(static_cast<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 = static_cast<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, nullptr) != 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 == nullptr) {
throw Error("cannot allocate alternative stack");
}
stack.ss_flags = 0;
if (sigaltstack(&stack, nullptr) == -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, nullptr) != 0) {
throw SysError("resetting SIGSEGV");
}
#endif
}
} // namespace nix
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