From 1ea8c59441cd215d4f45cbe839cbfe51c6e32068 Mon Sep 17 00:00:00 2001 From: Rob Norris Date: Fri, 10 May 2024 13:04:14 +1000 Subject: [PATCH] backtrace: rework for signal safety Mostly, try a lot harder to not allocate anything. Sponsored-by: Klara, Inc. Sponsored-by: Wasabi Technology, Inc. Reviewed-by: Brian Behlendorf Signed-off-by: Rob Norris Closes #16181 --- cmd/zdb/zdb.c | 2 +- cmd/ztest.c | 2 +- lib/libspl/assert.c | 2 +- lib/libspl/backtrace.c | 89 +++++++++++++++++++++--------- lib/libspl/include/sys/backtrace.h | 2 +- 5 files changed, 67 insertions(+), 30 deletions(-) diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c index 01d584844c0f..7c2819d3cf01 100644 --- a/cmd/zdb/zdb.c +++ b/cmd/zdb/zdb.c @@ -845,7 +845,7 @@ static void sig_handler(int signo) { struct sigaction action; - libspl_backtrace(); + libspl_backtrace(STDERR_FILENO); dump_debug_buffer(); /* diff --git a/cmd/ztest.c b/cmd/ztest.c index d6f22d04a6ee..b4d63b02dda6 100644 --- a/cmd/ztest.c +++ b/cmd/ztest.c @@ -623,7 +623,7 @@ static void sig_handler(int signo) { struct sigaction action; - libspl_backtrace(); + libspl_backtrace(STDERR_FILENO); dump_debug_buffer(); /* diff --git a/lib/libspl/assert.c b/lib/libspl/assert.c index ff0d17ba2a5e..d11361b387e2 100644 --- a/lib/libspl/assert.c +++ b/lib/libspl/assert.c @@ -103,7 +103,7 @@ libspl_assertf(const char *file, const char *func, int line, getpid(), libspl_getprogname(), libspl_gettid(), tname); - libspl_backtrace(); + libspl_backtrace(STDERR_FILENO); #if !__has_feature(attribute_analyzer_noreturn) && !defined(__COVERITY__) if (libspl_assert_ok) { diff --git a/lib/libspl/backtrace.c b/lib/libspl/backtrace.c index 0e653cd96434..dd8cb025f4f1 100644 --- a/lib/libspl/backtrace.c +++ b/lib/libspl/backtrace.c @@ -24,57 +24,94 @@ */ #include -#include +#include +#include + +/* + * libspl_backtrace() must be safe to call from inside a signal hander. This + * mostly means it must not allocate, and so we can't use things like printf. + */ #if defined(HAVE_LIBUNWIND) #define UNW_LOCAL_ONLY #include +static size_t +libspl_u64_to_hex_str(uint64_t v, size_t digits, char *buf, size_t buflen) +{ + static const char hexdigits[] = { + '0', '1', '2', '3', '4', '5', '6', '7', + '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' + }; + + size_t pos = 0; + boolean_t want = (digits == 0); + for (int i = 15; i >= 0; i--) { + const uint64_t d = v >> (i * 4) & 0xf; + if (!want && (d != 0 || digits > i)) + want = B_TRUE; + if (want) { + buf[pos++] = hexdigits[d]; + if (pos == buflen) + break; + } + } + return (pos); +} + void -libspl_backtrace(void) +libspl_backtrace(int fd) { + ssize_t ret __attribute__((unused)); unw_context_t uc; unw_cursor_t cp; - unw_word_t ip, off; - char funcname[128]; -#ifdef HAVE_LIBUNWIND_ELF - char objname[128]; - unw_word_t objoff; -#endif + unw_word_t loc; + char buf[128]; + size_t n; - fprintf(stderr, "Call trace:\n"); + ret = write(fd, "Call trace:\n", 12); unw_getcontext(&uc); unw_init_local(&cp, &uc); while (unw_step(&cp) > 0) { - unw_get_reg(&cp, UNW_REG_IP, &ip); - unw_get_proc_name(&cp, funcname, sizeof (funcname), &off); + unw_get_reg(&cp, UNW_REG_IP, &loc); + ret = write(fd, " [0x", 5); + n = libspl_u64_to_hex_str(loc, 10, buf, sizeof (buf)); + ret = write(fd, buf, n); + ret = write(fd, "] ", 2); + unw_get_proc_name(&cp, buf, sizeof (buf), &loc); + for (n = 0; n < sizeof (buf) && buf[n] != '\0'; n++) {} + ret = write(fd, buf, n); + ret = write(fd, "+0x", 3); + n = libspl_u64_to_hex_str(loc, 2, buf, sizeof (buf)); + ret = write(fd, buf, n); #ifdef HAVE_LIBUNWIND_ELF - unw_get_elf_filename(&cp, objname, sizeof (objname), &objoff); - fprintf(stderr, " [0x%08lx] %s+0x%2lx (in %s +0x%2lx)\n", - ip, funcname, off, objname, objoff); -#else - fprintf(stderr, " [0x%08lx] %s+0x%2lx\n", ip, funcname, off); + ret = write(fd, " (in ", 5); + unw_get_elf_filename(&cp, buf, sizeof (buf), &loc); + for (n = 0; n < sizeof (buf) && buf[n] != '\0'; n++) {} + ret = write(fd, buf, n); + ret = write(fd, " +0x", 4); + n = libspl_u64_to_hex_str(loc, 2, buf, sizeof (buf)); + ret = write(fd, buf, n); + ret = write(fd, ")", 1); #endif + ret = write(fd, "\n", 1); } } #elif defined(HAVE_BACKTRACE) #include void -libspl_backtrace(void) +libspl_backtrace(int fd) { - void *btptrs[100]; - size_t nptrs = backtrace(btptrs, 100); - char **bt = backtrace_symbols(btptrs, nptrs); - fprintf(stderr, "Call trace:\n"); - for (size_t i = 0; i < nptrs; i++) - fprintf(stderr, " %s\n", bt[i]); - free(bt); + ssize_t ret __attribute__((unused)); + void *btptrs[64]; + size_t nptrs = backtrace(btptrs, 64); + ret = write(fd, "Call trace:\n", 12); + backtrace_symbols_fd(btptrs, nptrs, fd); } #else void -libspl_backtrace(void) +libspl_backtrace(int fd __maybe_unused) { } #endif - diff --git a/lib/libspl/include/sys/backtrace.h b/lib/libspl/include/sys/backtrace.h index 97ee7740ce6f..f9869ffc9e1a 100644 --- a/lib/libspl/include/sys/backtrace.h +++ b/lib/libspl/include/sys/backtrace.h @@ -27,6 +27,6 @@ #ifndef _LIBSPL_SYS_BACKTRACE_H #define _LIBSPL_SYS_BACKTRACE_H -void libspl_backtrace(void); +void libspl_backtrace(int fd); #endif