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Optionally support lldb for stack traces and debugger attach (#11413) 

Summary:
lldb is more supported for Meta infrastructure than gdb, so adding support for it in generating stack traces and attaching debugger on crash. For now you need to set ROCKSDB_LLDB_STACK=1 for stack traces or ROCKSDB_DEBUG=lldb for interactive debugging.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11413

Test Plan: some manual testing (no production code changes)

Reviewed By: ajkr

Differential Revision: D45360952

Pulled By: pdillinger

fbshipit-source-id: 862bc8800eb03e3bdc1be8c0702960a19db45be8
This commit is contained in:
Peter Dillinger 2023-05-01 14:12:40 -07:00 committed by Facebook GitHub Bot
parent 76a40286b0
commit e0e318f370
1 changed files with 67 additions and 24 deletions
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91
port/stack_trace.cc
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@ -128,6 +128,14 @@ void PrintStackTraceLine(const char* symbol, void* frame) {
#endif #endif
const char* GetLldbScriptSelectThread(long long tid) {
// NOTE: called from a signal handler, so no heap allocation
static char script[80];
snprintf(script, sizeof(script),
"script -l python -- lldb.process.SetSelectedThreadByID(%lld)", tid);
return script;
}
} // namespace } // namespace
void PrintStack(void* frames[], int num_frames) { void PrintStack(void* frames[], int num_frames) {
@ -152,9 +160,13 @@ void PrintStack(int first_frames_to_skip) {
// * It doesn't appear easy to detect when ASLR is in use. // * It doesn't appear easy to detect when ASLR is in use.
// * With DEBUG_LEVEL < 2, backtrace() can skip frames that are not skipped // * With DEBUG_LEVEL < 2, backtrace() can skip frames that are not skipped
// in GDB. // in GDB.
//
// LLDB also available as an option
bool lldb_stack_trace = getenv("ROCKSDB_LLDB_STACK") != nullptr;
#if defined(OS_LINUX) #if defined(OS_LINUX)
// Default true, override with ROCKSDB_BACKTRACE_STACK=1 // Default true, override with ROCKSDB_BACKTRACE_STACK=1
bool gdb_stack_trace = getenv("ROCKSDB_BACKTRACE_STACK") == nullptr; bool gdb_stack_trace =
!lldb_stack_trace && getenv("ROCKSDB_BACKTRACE_STACK") == nullptr;
#else #else
// Default false, override with ROCKSDB_GDB_STACK=1 // Default false, override with ROCKSDB_GDB_STACK=1
bool gdb_stack_trace = getenv("ROCKSDB_GDB_STACK") != nullptr; bool gdb_stack_trace = getenv("ROCKSDB_GDB_STACK") != nullptr;
@ -164,53 +176,84 @@ void PrintStack(int first_frames_to_skip) {
char* debug_env = getenv("ROCKSDB_DEBUG"); char* debug_env = getenv("ROCKSDB_DEBUG");
bool debug = debug_env != nullptr && strlen(debug_env) > 0; bool debug = debug_env != nullptr && strlen(debug_env) > 0;
if (gdb_stack_trace || debug) { if (lldb_stack_trace || gdb_stack_trace || debug) {
// Allow ouside debugger to attach, even with Yama security restrictions // Allow ouside debugger to attach, even with Yama security restrictions
#ifdef PR_SET_PTRACER_ANY #ifdef PR_SET_PTRACER_ANY
(void)prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0); (void)prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
#endif #endif
// Try to invoke GDB, either for stack trace or debugging. // Try to invoke GDB, either for stack trace or debugging.
long long attach_id = getpid(); long long attach_pid = getpid();
// NOTE: we're in a signal handler, so no heap allocation
char attach_pid_str[20];
snprintf(attach_pid_str, sizeof(attach_pid_str), "%lld", attach_pid);
// `gdb -p PID` seems to always attach to main thread, but `gdb -p TID` // `gdb -p PID` seems to always attach to main thread, but `gdb -p TID`
// seems to be able to attach to a particular thread in a process, which // seems to be able to attach to a particular thread in a process, which
// makes sense as the main thread TID == PID of the process. // makes sense as the main thread TID == PID of the process.
// But I haven't found that gdb capability documented anywhere, so leave // But I haven't found that gdb capability documented anywhere, so leave
// a back door to attach to main thread. // a back door to attach to main thread.
long long gdb_attach_id = attach_pid;
// Save current thread id before fork
long long attach_tid = 0;
#ifdef OS_LINUX #ifdef OS_LINUX
attach_tid = gettid();
if (getenv("ROCKSDB_DEBUG_USE_PID") == nullptr) { if (getenv("ROCKSDB_DEBUG_USE_PID") == nullptr) {
attach_id = gettid(); gdb_attach_id = attach_tid;
} }
#endif #endif
char attach_id_str[20];
snprintf(attach_id_str, sizeof(attach_id_str), "%lld", attach_id); char gdb_attach_id_str[20];
snprintf(gdb_attach_id_str, sizeof(gdb_attach_id_str), "%lld",
gdb_attach_id);
pid_t child_pid = fork(); pid_t child_pid = fork();
if (child_pid == 0) { if (child_pid == 0) {
// child process // child process
if (debug) { if (debug) {
fprintf(stderr, "Invoking GDB for debugging (ROCKSDB_DEBUG=%s)...\n", if (strcmp(debug_env, "lldb") == 0) {
debug_env); fprintf(stderr, "Invoking LLDB for debugging (ROCKSDB_DEBUG=%s)...\n",
execlp(/*cmd in PATH*/ "gdb", /*arg0*/ "gdb", "-p", attach_id_str, debug_env);
(char*)nullptr); execlp(/*cmd in PATH*/ "lldb", /*arg0*/ "lldb", "-p", attach_pid_str,
return; /*"-Q",*/ "-o", GetLldbScriptSelectThread(attach_tid),
(char*)nullptr);
return;
} else {
fprintf(stderr, "Invoking GDB for debugging (ROCKSDB_DEBUG=%s)...\n",
debug_env);
execlp(/*cmd in PATH*/ "gdb", /*arg0*/ "gdb", "-p", gdb_attach_id_str,
(char*)nullptr);
return;
}
} else { } else {
fprintf(stderr, "Invoking GDB for stack trace...\n");
// Skip top ~4 frames here in PrintStack
// See https://stackoverflow.com/q/40991943/454544
auto bt_in_gdb =
"frame apply level 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 "
"21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 "
"42 43 44 -q frame";
// Redirect child stdout to original stderr // Redirect child stdout to original stderr
dup2(2, 1); dup2(2, 1);
// No child stdin (don't use pager) // No child stdin (don't use pager)
close(0); close(0);
// -n : Loading config files can apparently cause failures with the if (lldb_stack_trace) {
// other options here. fprintf(stderr, "Invoking LLDB for stack trace...\n");
// -batch : non-interactive; suppress banners as much as possible
execlp(/*cmd in PATH*/ "gdb", /*arg0*/ "gdb", "-n", "-batch", "-p", // Skip top ~8 frames here in PrintStack
attach_id_str, "-ex", bt_in_gdb, (char*)nullptr); auto bt_in_lldb =
"script -l python -- for f in lldb.thread.frames[8:]: print(f)";
execlp(/*cmd in PATH*/ "lldb", /*arg0*/ "lldb", "-p", attach_pid_str,
"-b", "-Q", "-o", GetLldbScriptSelectThread(attach_tid), "-o",
bt_in_lldb, (char*)nullptr);
} else {
// gdb_stack_trace
fprintf(stderr, "Invoking GDB for stack trace...\n");
// Skip top ~4 frames here in PrintStack
// See https://stackoverflow.com/q/40991943/454544
auto bt_in_gdb =
"frame apply level 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 "
"21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 "
"42 43 44 -q frame";
// -n : Loading config files can apparently cause failures with the
// other options here.
// -batch : non-interactive; suppress banners as much as possible
execlp(/*cmd in PATH*/ "gdb", /*arg0*/ "gdb", "-n", "-batch", "-p",
gdb_attach_id_str, "-ex", bt_in_gdb, (char*)nullptr);
}
return; return;
} }
} else { } else {