#759: Discover available profiling signal automatically

async-profiler · Mar 16, 2024 · 397f450 · 397f450
1 parent 1be8838
commit 397f450
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Showing 6 changed files with 59 additions and 3 deletions.
diff --git a/src/ctimer_linux.cpp b/src/ctimer_linux.cpp
@@ -97,7 +97,7 @@ Error CTimer::start(Arguments& args) {
     }
     _interval = args._interval ? args._interval : DEFAULT_INTERVAL;
     _cstack = args._cstack;
-    _signal = args._signal == 0 ? SIGPROF : args._signal & 0xff;
+    _signal = args._signal == 0 ? OS::getProfilingSignal(0) : args._signal & 0xff;
 
     int max_timers = OS::getMaxThreadId();
     if (max_timers != _max_timers) {

diff --git a/src/os.h b/src/os.h
@@ -72,6 +72,7 @@ class OS {
 
     static SigAction installSignalHandler(int signo, SigAction action, SigHandler handler = NULL);
     static SigAction replaceCrashHandler(SigAction action);
+    static int getProfilingSignal(int mode);
     static bool sendSignalToThread(int thread_id, int signo);
 
     static void* safeAlloc(size_t size);

diff --git a/src/os_linux.cpp b/src/os_linux.cpp
@@ -107,6 +107,8 @@ JitWriteProtection::~JitWriteProtection() {
 }
 
 
+static SigAction installed_sigaction[64];
+
 const size_t OS::page_size = sysconf(_SC_PAGESIZE);
 const size_t OS::page_mask = OS::page_size - 1;
 
@@ -235,6 +237,9 @@ SigAction OS::installSignalHandler(int signo, SigAction action, SigHandler handl
     } else {
         sa.sa_sigaction = action;
         sa.sa_flags = SA_SIGINFO | SA_RESTART;
+        if (signo > 0 && signo < sizeof(installed_sigaction) / sizeof(installed_sigaction[0])) {
+            installed_sigaction[signo] = action;
+        }
     }
 
     sigaction(signo, &sa, &oldsa);
@@ -250,6 +255,28 @@ SigAction OS::replaceCrashHandler(SigAction action) {
     return old_action;
 }
 
+int OS::getProfilingSignal(int mode) {
+    static int preferred_signals[2] = {SIGPROF, SIGVTALRM};
+
+    const u64 allowed_signals =
+        1ULL << SIGPROF | 1ULL << SIGVTALRM | 1ULL << SIGSTKFLT | 1ULL << SIGPWR | -(1ULL << SIGRTMIN);
+
+    int& signo = preferred_signals[mode];
+    int initial_signo = signo;
+    int other_signo = preferred_signals[1 - mode];
+
+    do {
+        struct sigaction sa;
+        if ((allowed_signals & (1ULL << signo)) != 0 && signo != other_signo && sigaction(signo, NULL, &sa) == 0) {
+            if (sa.sa_handler == SIG_DFL || sa.sa_handler == SIG_IGN || sa.sa_sigaction == installed_sigaction[signo]) {
+                return signo;
+            }
+        }
+    } while ((signo = (signo + 53) & 63) != initial_signo);
+
+    return signo;
+}
+
 bool OS::sendSignalToThread(int thread_id, int signo) {
     return syscall(__NR_tgkill, processId(), thread_id, signo) == 0;
 }

diff --git a/src/os_macos.cpp b/src/os_macos.cpp
@@ -104,6 +104,8 @@ JitWriteProtection::~JitWriteProtection() {
 }
 
 
+static SigAction installed_sigaction[32];
+
 const size_t OS::page_size = sysconf(_SC_PAGESIZE);
 const size_t OS::page_mask = OS::page_size - 1;
 
@@ -204,6 +206,9 @@ SigAction OS::installSignalHandler(int signo, SigAction action, SigHandler handl
     } else {
         sa.sa_sigaction = action;
         sa.sa_flags = SA_SIGINFO | SA_RESTART;
+        if (signo > 0 && signo < sizeof(installed_sigaction) / sizeof(installed_sigaction[0])) {
+            installed_sigaction[signo] = action;
+        }
     }
 
     sigaction(signo, &sa, &oldsa);
@@ -219,6 +224,28 @@ SigAction OS::replaceCrashHandler(SigAction action) {
     return old_action;
 }
 
+int OS::getProfilingSignal(int mode) {
+    static int preferred_signals[2] = {SIGPROF, SIGVTALRM};
+
+    const u64 allowed_signals =
+        1ULL << SIGPROF | 1ULL << SIGVTALRM | 1ULL << SIGEMT | 1ULL << SIGSYS;
+
+    int& signo = preferred_signals[mode];
+    int initial_signo = signo;
+    int other_signo = preferred_signals[1 - mode];
+
+    do {
+        struct sigaction sa;
+        if ((allowed_signals & (1ULL << signo)) != 0 && signo != other_signo && sigaction(signo, NULL, &sa) == 0) {
+            if (sa.sa_handler == SIG_DFL || sa.sa_handler == SIG_IGN || sa.sa_sigaction == installed_sigaction[signo]) {
+                return signo;
+            }
+        }
+    } while ((signo = (signo + 1) & 31) != initial_signo);
+
+    return signo;
+}
+
 bool OS::sendSignalToThread(int thread_id, int signo) {
 #ifdef __aarch64__
     register long x0 asm("x0") = thread_id;

diff --git a/src/perfEvents_linux.cpp b/src/perfEvents_linux.cpp
@@ -779,7 +779,7 @@ Error PerfEvents::start(Arguments& args) {
     }
     _interval = args._interval ? args._interval : _event_type->default_interval;
     _cstack = args._cstack;
-    _signal = args._signal == 0 ? SIGPROF : args._signal & 0xff;
+    _signal = args._signal == 0 ? OS::getProfilingSignal(0) : args._signal & 0xff;
 
     _ring = args._ring;
     if (_ring != RING_USER && !Symbols::haveKernelSymbols()) {

diff --git a/src/wallClock.cpp b/src/wallClock.cpp
@@ -70,7 +70,8 @@ Error WallClock::start(Arguments& args) {
         _interval = _sample_idle_threads ? DEFAULT_INTERVAL * 5 : DEFAULT_INTERVAL;
     }
 
-    _signal = args._signal == 0 ? SIGVTALRM : ((args._signal >> 8) > 0 ? args._signal >> 8 : args._signal);
+    _signal = args._signal == 0 ? OS::getProfilingSignal(1)
+                                : ((args._signal >> 8) > 0 ? args._signal >> 8 : args._signal);
     OS::installSignalHandler(_signal, signalHandler);
 
     _running = true;