Commit 799647dd authored Dec 02, 2025 by Josh Poimboeuf Committed by Ingo Molnar Dec 03, 2025

objtool: Add more robust signal error handling, detect and warn about stack overflows



When the kernel build fails due to an objtool segfault, the error
message is a bit obtuse and confusing:

  make[5]: *** [scripts/Makefile.build:503: drivers/scsi/qla2xxx/qla2xxx.o] Error 139
                                                                            ^^^^^^^^^
  make[5]: *** Deleting file 'drivers/scsi/qla2xxx/qla2xxx.o'
  make[4]: *** [scripts/Makefile.build:556: drivers/scsi/qla2xxx] Error 2
  make[3]: *** [scripts/Makefile.build:556: drivers/scsi] Error 2
  make[2]: *** [scripts/Makefile.build:556: drivers] Error 2
  make[1]: *** [/home/jpoimboe/git/linux/Makefile:2013: .] Error 2
  make: *** [Makefile:248: __sub-make] Error 2

Add a signal handler to objtool which prints an error message like if
the local stack has overflown (for which there's a chance as objtool
makes heavy use of recursion):

  drivers/scsi/qla2xxx/qla2xxx.o: error: SIGSEGV: objtool stack overflow!

or:

  drivers/scsi/qla2xxx/qla2xxx.o: error: SIGSEGV: objtool crash!

Also, re-raise the signal so the core dump still gets triggered.

[ mingo: Applied a build fix, added more comments and prettified the code. ]

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: David Laight <david.laight.linux@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/mi4tihk4dbncn7belrhp6ooudhpw4vdggerktu5333w3gqf3uf@vqlhc3y667mg

parent ed3bf863

tools/objtool/Build

+1 −0

Original line number	Diff line number	Diff line
		@@ -18,6 +18,7 @@ objtool-y += libstring.o
		objtool-y += libctype.o
		objtool-y += str_error_r.o
		objtool-y += librbtree.o
		objtool-y += signal.o

		$(OUTPUT)libstring.o: ../lib/string.c FORCE
		$(call rule_mkdir)

tools/objtool/include/objtool/objtool.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -41,6 +41,8 @@ struct objtool_file {

		char top_level_dir(const char file);

		int init_signal_handler(void);

		struct objtool_file objtool_open_read(const char _objname);

		int objtool_pv_add(struct objtool_file file, int idx, struct symbol func);

tools/objtool/objtool.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -104,11 +104,13 @@ char top_level_dir(const char file)
		return str;
		}


		int main(int argc, const char **argv)
		{
		static const char *UNUSED = "OBJTOOL_NOT_IMPLEMENTED";

		if (init_signal_handler())
		return -1;

		/* libsubcmd init */
		exec_cmd_init("objtool", UNUSED, UNUSED, UNUSED);
		pager_init(UNUSED);

tools/objtool/signal.c

0 → 100644

+135 −0

Original line number	Diff line number	Diff line
		/*
		* signal.c: Register a sigaltstack for objtool, to be able to
		* run a signal handler on a separate stack even if
		* the main process stack has overflown. Print out
		* stack overflow errors when this happens.
		*/
		#include <stdio.h>
		#include <stdlib.h>
		#include <signal.h>
		#include <unistd.h>
		#include <sys/resource.h>
		#include <string.h>

		#include <objtool/objtool.h>
		#include <objtool/warn.h>

		static unsigned long stack_limit;

		static bool is_stack_overflow(void *fault_addr)
		{
		unsigned long fault = (unsigned long)fault_addr;

		/* Check if fault is in the guard page just below the limit. */
		return fault < stack_limit && fault >= stack_limit - 4096;
		}

		static void signal_handler(int sig_num, siginfo_t info, void context)
		{
		struct sigaction sa_dfl = {0};
		const char *sig_name;
		char msg[256];
		int msg_len;

		switch (sig_num) {
		case SIGSEGV: sig_name = "SIGSEGV"; break;
		case SIGBUS: sig_name = "SIGBUS"; break;
		case SIGILL: sig_name = "SIGILL"; break;
		case SIGABRT: sig_name = "SIGABRT"; break;
		default: sig_name = "Unknown signal"; break;
		}

		if (is_stack_overflow(info->si_addr)) {
		msg_len = snprintf(msg, sizeof(msg),
		"%s: error: %s: objtool stack overflow!\n",
		objname, sig_name);
		} else {
		msg_len = snprintf(msg, sizeof(msg),
		"%s: error: %s: objtool crash!\n",
		objname, sig_name);
		}

		msg_len = write(STDERR_FILENO, msg, msg_len);

		/* Re-raise the signal to trigger the core dump */
		sa_dfl.sa_handler = SIG_DFL;
		sigaction(sig_num, &sa_dfl, NULL);
		raise(sig_num);
		}

		static int read_stack_limit(void)
		{
		unsigned long stack_start, stack_end;
		struct rlimit rlim;
		char line[256];
		int ret = 0;
		FILE *fp;

		if (getrlimit(RLIMIT_STACK, &rlim)) {
		ERROR_GLIBC("getrlimit");
		return -1;
		}

		fp = fopen("/proc/self/maps", "r");
		if (!fp) {
		ERROR_GLIBC("fopen");
		return -1;
		}

		while (fgets(line, sizeof(line), fp)) {
		if (strstr(line, "[stack]")) {
		if (sscanf(line, "%lx-%lx", &stack_start, &stack_end) != 2) {
		ERROR_GLIBC("sscanf");
		ret = -1;
		goto done;
		}
		stack_limit = stack_end - rlim.rlim_cur;
		goto done;
		}
		}

		ret = -1;
		ERROR("/proc/self/maps: can't find [stack]");

		done:
		fclose(fp);

		return ret;
		}

		int init_signal_handler(void)
		{
		int signals[] = {SIGSEGV, SIGBUS, SIGILL, SIGABRT};
		struct sigaction sa;
		stack_t ss;

		if (read_stack_limit())
		return -1;

		ss.ss_sp = malloc(SIGSTKSZ);
		if (!ss.ss_sp) {
		ERROR_GLIBC("malloc");
		return -1;
		}
		ss.ss_size = SIGSTKSZ;
		ss.ss_flags = 0;

		if (sigaltstack(&ss, NULL) == -1) {
		ERROR_GLIBC("sigaltstack");
		return -1;
		}

		sa.sa_sigaction = signal_handler;
		sigemptyset(&sa.sa_mask);

		sa.sa_flags = SA_ONSTACK \| SA_SIGINFO;

		for (int i = 0; i < ARRAY_SIZE(signals); i++) {
		if (sigaction(signals[i], &sa, NULL) == -1) {
		ERROR_GLIBC("sigaction");
		return -1;
		}
		}

		return 0;
		}