fix sigaction double panic

Fixes #8357

lib/std/debug.zig

@@ -1689,6 +1689,12 @@ pub fn maybeEnableSegfaultHandler() void {
 
 var windows_segfault_handle: ?windows.HANDLE = null;
 
+pub fn updateSegfaultHandler(act: ?*const os.Sigaction) error{OperationNotSupported}!void {
+    try os.sigaction(os.SIG.SEGV, act, null);
+    try os.sigaction(os.SIG.ILL, act, null);
+    try os.sigaction(os.SIG.BUS, act, null);
+}
+
 /// Attaches a global SIGSEGV handler which calls @panic("segmentation fault");
 pub fn attachSegfaultHandler() void {
     if (!have_segfault_handling_support) {
@@ -1704,9 +1710,9 @@ pub fn attachSegfaultHandler() void {
         .flags = (os.SA.SIGINFO | os.SA.RESTART | os.SA.RESETHAND),
     };
 
-    os.sigaction(os.SIG.SEGV, &act, null);
-    os.sigaction(os.SIG.ILL, &act, null);
-    os.sigaction(os.SIG.BUS, &act, null);
+    updateSegfaultHandler(&act) catch {
+        @panic("unable to install segfault handler, maybe adjust have_segfault_handling_support in std/debug.zig");
+    };
 }
 
 fn resetSegfaultHandler() void {
@@ -1722,9 +1728,8 @@ fn resetSegfaultHandler() void {
         .mask = os.empty_sigset,
         .flags = 0,
     };
-    os.sigaction(os.SIG.SEGV, &act, null);
-    os.sigaction(os.SIG.ILL, &act, null);
-    os.sigaction(os.SIG.BUS, &act, null);
+    // do nothing if an error happens to avoid a double-panic
+    updateSegfaultHandler(&act) catch {};
 }
 
 fn handleSegfaultPosix(sig: i32, info: *const os.siginfo_t, ctx_ptr: ?*const anyopaque) callconv(.C) noreturn {

lib/std/os.zig

@@ -5521,11 +5521,10 @@ pub fn sigaltstack(ss: ?*stack_t, old_ss: ?*stack_t) SigaltstackError!void {
 }
 
 /// Examine and change a signal action.
-pub fn sigaction(sig: u6, act: ?*const Sigaction, oact: ?*Sigaction) void {
+pub fn sigaction(sig: u6, noalias act: ?*const Sigaction, noalias oact: ?*Sigaction) error{OperationNotSupported}!void {
     switch (errno(system.sigaction(sig, act, oact))) {
         .SUCCESS => return,
-        .FAULT => unreachable,
-        .INVAL => unreachable,
+        .INVAL, .NOSYS => return error.OperationNotSupported,
         else => unreachable,
     }
 }

lib/std/os/test.zig

@@ -772,16 +772,16 @@ test "sigaction" {
     };
     var old_sa: os.Sigaction = undefined;
     // Install the new signal handler.
-    os.sigaction(os.SIG.USR1, &sa, null);
+    try os.sigaction(os.SIG.USR1, &sa, null);
     // Check that we can read it back correctly.
-    os.sigaction(os.SIG.USR1, null, &old_sa);
+    try os.sigaction(os.SIG.USR1, null, &old_sa);
     try testing.expectEqual(S.handler, old_sa.handler.sigaction.?);
     try testing.expect((old_sa.flags & os.SA.SIGINFO) != 0);
     // Invoke the handler.
     try os.raise(os.SIG.USR1);
     try testing.expect(signal_test_failed == false);
     // Check if the handler has been correctly reset to SIG_DFL
-    os.sigaction(os.SIG.USR1, null, &old_sa);
+    try os.sigaction(os.SIG.USR1, null, &old_sa);
     try testing.expectEqual(os.SIG.DFL, old_sa.handler.sigaction);
 }
 

src/crash_report.zig

@@ -175,9 +175,9 @@ pub fn attachSegfaultHandler() void {
         .flags = (os.SA.SIGINFO | os.SA.RESTART | os.SA.RESETHAND),
     };
 
-    os.sigaction(os.SIG.SEGV, &act, null);
-    os.sigaction(os.SIG.ILL, &act, null);
-    os.sigaction(os.SIG.BUS, &act, null);
+    debug.updateSegfaultHandler(&act) catch {
+        @panic("unable to install segfault handler, maybe adjust have_segfault_handling_support in std/debug.zig");
+    };
 }
 
 fn handleSegfaultPosix(sig: i32, info: *const os.siginfo_t, ctx_ptr: ?*const anyopaque) callconv(.C) noreturn {