tests/kernel: Add floating-point exceptions test.

Tests #18624 and related issues.

src/tests/system/kernel/Jamfile

@@ -16,6 +16,8 @@ local avxSource = [ FGristFiles hello_avx.c ] ;
 local avxObject = $(avxSource:S=$(SUFOBJ)) ;
 CCFLAGS on $(avxObject) = -mavx ;
 
+SimpleTest fp_excepts_test : fp_excepts.c ;
+
 SimpleTest live_query :
 	live_query.cpp
 	: be [ TargetLibsupc++ ]

src/tests/system/kernel/fp_excepts.c

@@ -0,0 +1,91 @@
+#define _DEFAULT_SOURCE
+#include <assert.h>
+#include <errno.h>
+#include <fenv.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+
+
+static int sExceptions = 0;
+static int sLastCode = -1;
+static jmp_buf sJmpBuf;
+
+
+static void
+signal_handler(int signal, siginfo_t* siginfo, void*)
+{
+	sExceptions++;
+	sLastCode = siginfo->si_code;
+
+	longjmp(sJmpBuf, 1);
+}
+
+
+int main()
+{
+	fenv_t exceptenv;
+	long double volatile nanl, resultl;
+
+	struct sigaction action = {};
+	sigemptyset(&action.sa_mask);
+	action.sa_flags = SA_SIGINFO | SA_NODEFER | SA_NOMASK;
+	action.sa_sigaction = signal_handler;
+	if (sigaction(SIGFPE, &action, NULL) == -1) {
+		fprintf(stderr, "failed to install signal handler: %s\n",
+			strerror(errno));
+		return 1;
+	}
+
+	assert(feclearexcept(FE_ALL_EXCEPT) == 0);
+
+	// Test 1: switching to an fenv with an exception raised triggers SIGFPE
+	// (but not a kernel panic.)
+	if (feenableexcept(FE_INVALID) == -1) {
+		fputs("trapping floating-point exceptions are not supported on this machine.\n", stderr);
+		return -1;
+	}
+
+	assert(fegetenv(&exceptenv) == 0);
+	assert(fesetenv(FE_DFL_ENV) == 0);
+
+	assert(feraiseexcept(FE_INVALID) == 0);
+
+	assert(sExceptions == 0);
+	if (setjmp(sJmpBuf) == 0) {
+		assert(feupdateenv(&exceptenv) == 0);
+	} else {
+		assert(feclearexcept(FE_INVALID) == 0);
+		assert(feupdateenv(&exceptenv) == 0);
+	}
+	assert(sExceptions == 1);
+	assert(sLastCode == FPE_FLTINV);
+
+	// Test 2: long signaling NaNs also trigger SIGFPE
+	// (but again no kernel panic.)
+	nanl = __builtin_nansl("");
+	assert(sExceptions == 1);
+	if (setjmp(sJmpBuf) == 0) {
+		resultl = nanl + 42.0L;
+	} else {
+		assert(feclearexcept(FE_ALL_EXCEPT) == 0);
+	}
+	assert(sExceptions == 2);
+	assert(sLastCode == FPE_FLTINV);
+
+	// Test 3: Overflow triggers SIGFPE, with the right code.
+	if (feenableexcept(FE_OVERFLOW) == -1) {
+		fputs("FE_OVERFLOW is not supported on this machine.\n", stderr);
+		return 0;
+	}
+
+	if (setjmp(sJmpBuf) == 0) {
+		float volatile top = FLT_MAX;
+		float volatile result = top * top;
+	}
+	assert(sExceptions == 3);
+	assert(sLastCode == FPE_FLTOVF);
+
+	return 0;
+}