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std.debug: fix segfault/panic race condition
closes #7859 closes #12207
This commit is contained in:
Andrew Kelley
parent
2ee328995a
commit
95ac94b7ac
@ -334,6 +334,7 @@ pub fn panicImpl(trace: ?*const std.builtin.StackTrace, first_trace_addr: ?usize
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resetSegfaultHandler();
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}
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// Note there is similar logic in handleSegfaultPosix and handleSegfaultWindowsExtra.
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nosuspend switch (panic_stage) {
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0 => {
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panic_stage = 1;
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@ -359,16 +360,7 @@ pub fn panicImpl(trace: ?*const std.builtin.StackTrace, first_trace_addr: ?usize
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dumpCurrentStackTrace(first_trace_addr);
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}
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if (panicking.fetchSub(1, .SeqCst) != 1) {
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// Another thread is panicking, wait for the last one to finish
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// and call abort()
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if (builtin.single_threaded) unreachable;
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// Sleep forever without hammering the CPU
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var futex = std.atomic.Atomic(u32).init(0);
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while (true) std.Thread.Futex.wait(&futex, 0);
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unreachable;
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}
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waitForOtherThreadToFinishPanicking();
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},
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1 => {
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panic_stage = 2;
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@ -387,6 +379,20 @@ pub fn panicImpl(trace: ?*const std.builtin.StackTrace, first_trace_addr: ?usize
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os.abort();
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}
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/// Must be called only after adding 1 to `panicking`. There are three callsites.
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fn waitForOtherThreadToFinishPanicking() void {
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if (panicking.fetchSub(1, .SeqCst) != 1) {
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// Another thread is panicking, wait for the last one to finish
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// and call abort()
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if (builtin.single_threaded) unreachable;
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// Sleep forever without hammering the CPU
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var futex = std.atomic.Atomic(u32).init(0);
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while (true) std.Thread.Futex.wait(&futex, 0);
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unreachable;
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}
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}
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pub fn writeStackTrace(
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stack_trace: std.builtin.StackTrace,
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out_stream: anytype,
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@ -1971,17 +1977,41 @@ fn handleSegfaultPosix(sig: i32, info: *const os.siginfo_t, ctx_ptr: ?*const any
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else => unreachable,
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};
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// Don't use std.debug.print() as stderr_mutex may still be locked.
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nosuspend {
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const stderr = io.getStdErr().writer();
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_ = switch (sig) {
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os.SIG.SEGV => stderr.print("Segmentation fault at address 0x{x}\n", .{addr}),
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os.SIG.ILL => stderr.print("Illegal instruction at address 0x{x}\n", .{addr}),
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os.SIG.BUS => stderr.print("Bus error at address 0x{x}\n", .{addr}),
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os.SIG.FPE => stderr.print("Arithmetic exception at address 0x{x}\n", .{addr}),
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else => unreachable,
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} catch os.abort();
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}
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nosuspend switch (panic_stage) {
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0 => {
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panic_stage = 1;
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_ = panicking.fetchAdd(1, .SeqCst);
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{
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panic_mutex.lock();
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defer panic_mutex.unlock();
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dumpSegfaultInfoPosix(sig, addr, ctx_ptr);
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}
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waitForOtherThreadToFinishPanicking();
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},
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else => {
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// panic mutex already locked
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dumpSegfaultInfoPosix(sig, addr, ctx_ptr);
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},
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};
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// We cannot allow the signal handler to return because when it runs the original instruction
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// again, the memory may be mapped and undefined behavior would occur rather than repeating
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// the segfault. So we simply abort here.
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os.abort();
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}
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fn dumpSegfaultInfoPosix(sig: i32, addr: usize, ctx_ptr: ?*const anyopaque) void {
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const stderr = io.getStdErr().writer();
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_ = switch (sig) {
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os.SIG.SEGV => stderr.print("Segmentation fault at address 0x{x}\n", .{addr}),
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os.SIG.ILL => stderr.print("Illegal instruction at address 0x{x}\n", .{addr}),
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os.SIG.BUS => stderr.print("Bus error at address 0x{x}\n", .{addr}),
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os.SIG.FPE => stderr.print("Arithmetic exception at address 0x{x}\n", .{addr}),
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else => unreachable,
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} catch os.abort();
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switch (native_arch) {
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.x86 => {
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@ -2033,11 +2063,6 @@ fn handleSegfaultPosix(sig: i32, info: *const os.siginfo_t, ctx_ptr: ?*const any
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},
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else => {},
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}
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// We cannot allow the signal handler to return because when it runs the original instruction
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// again, the memory may be mapped and undefined behavior would occur rather than repeating
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// the segfault. So we simply abort here.
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os.abort();
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}
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fn handleSegfaultWindows(info: *windows.EXCEPTION_POINTERS) callconv(windows.WINAPI) c_long {
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@ -2050,27 +2075,36 @@ fn handleSegfaultWindows(info: *windows.EXCEPTION_POINTERS) callconv(windows.WIN
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}
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}
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// zig won't let me use an anon enum here https://github.com/ziglang/zig/issues/3707
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fn handleSegfaultWindowsExtra(info: *windows.EXCEPTION_POINTERS, comptime msg: u8, comptime format: ?[]const u8) noreturn {
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fn handleSegfaultWindowsExtra(
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info: *windows.EXCEPTION_POINTERS,
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msg: u8,
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label: ?[]const u8,
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) noreturn {
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const exception_address = @ptrToInt(info.ExceptionRecord.ExceptionAddress);
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if (@hasDecl(windows, "CONTEXT")) {
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const regs = info.ContextRecord.getRegs();
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// Don't use std.debug.print() as stderr_mutex may still be locked.
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nosuspend {
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const stderr = io.getStdErr().writer();
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_ = switch (msg) {
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0 => stderr.print("{s}\n", .{format.?}),
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1 => stderr.print("Segmentation fault at address 0x{x}\n", .{info.ExceptionRecord.ExceptionInformation[1]}),
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2 => stderr.print("Illegal instruction at address 0x{x}\n", .{regs.ip}),
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else => unreachable,
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} catch os.abort();
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}
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nosuspend switch (panic_stage) {
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0 => {
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panic_stage = 1;
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_ = panicking.fetchAdd(1, .SeqCst);
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dumpStackTraceFromBase(regs.bp, regs.ip);
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{
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panic_mutex.lock();
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defer panic_mutex.unlock();
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dumpSegfaultInfoWindows(info, msg, label);
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}
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waitForOtherThreadToFinishPanicking();
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},
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else => {
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// panic mutex already locked
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dumpSegfaultInfoWindows(info, msg, label);
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},
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};
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os.abort();
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} else {
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switch (msg) {
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0 => panicImpl(null, exception_address, format.?),
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0 => panicImpl(null, exception_address, "{s}", label.?),
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1 => {
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const format_item = "Segmentation fault at address 0x{x}";
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var buf: [format_item.len + 64]u8 = undefined; // 64 is arbitrary, but sufficiently large
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@ -2083,6 +2117,19 @@ fn handleSegfaultWindowsExtra(info: *windows.EXCEPTION_POINTERS, comptime msg: u
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}
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}
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fn dumpSegfaultInfoWindows(info: *windows.EXCEPTION_POINTERS, msg: u8, label: ?[]const u8) void {
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const regs = info.ContextRecord.getRegs();
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const stderr = io.getStdErr().writer();
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_ = switch (msg) {
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0 => stderr.print("{s}\n", .{label.?}),
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1 => stderr.print("Segmentation fault at address 0x{x}\n", .{info.ExceptionRecord.ExceptionInformation[1]}),
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2 => stderr.print("Illegal instruction at address 0x{x}\n", .{regs.ip}),
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else => unreachable,
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} catch os.abort();
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dumpStackTraceFromBase(regs.bp, regs.ip);
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}
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pub fn dumpStackPointerAddr(prefix: []const u8) void {
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const sp = asm (""
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: [argc] "={rsp}" (-> usize),
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