10 files changed, 157 insertions, 6 deletions
diff --git a/src/runtime/arch_386.go b/src/runtime/arch_386.go
index 4e9cce72b..90ec8e8ba 100644
--- a/src/runtime/arch_386.go
+++ b/src/runtime/arch_386.go
@@ -9,7 +9,12 @@ const deferExtraRegs = 0
 
 const callInstSize = 5 // "call someFunction" is 5 bytes
 
-const linux_MAP_ANONYMOUS = 0x20
+const (
+	linux_MAP_ANONYMOUS = 0x20
+	linux_SIGBUS        = 7
+	linux_SIGILL        = 4
+	linux_SIGSEGV       = 11
+)
 
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
diff --git a/src/runtime/arch_amd64.go b/src/runtime/arch_amd64.go
index 3bb03e3c7..436d6e384 100644
--- a/src/runtime/arch_amd64.go
+++ b/src/runtime/arch_amd64.go
@@ -9,7 +9,12 @@ const deferExtraRegs = 0
 
 const callInstSize = 5 // "call someFunction" is 5 bytes
 
-const linux_MAP_ANONYMOUS = 0x20
+const (
+	linux_MAP_ANONYMOUS = 0x20
+	linux_SIGBUS        = 7
+	linux_SIGILL        = 4
+	linux_SIGSEGV       = 11
+)
 
 // Align a pointer.
 // Note that some amd64 instructions (like movaps) expect 16-byte aligned
diff --git a/src/runtime/arch_arm.go b/src/runtime/arch_arm.go
index e28e85410..ea6b540d2 100644
--- a/src/runtime/arch_arm.go
+++ b/src/runtime/arch_arm.go
@@ -11,7 +11,12 @@ const deferExtraRegs = 0
 
 const callInstSize = 4 // "bl someFunction" is 4 bytes
 
-const linux_MAP_ANONYMOUS = 0x20
+const (
+	linux_MAP_ANONYMOUS = 0x20
+	linux_SIGBUS        = 7
+	linux_SIGILL        = 4
+	linux_SIGSEGV       = 11
+)
 
 // Align on the maximum alignment for this platform (double).
 func align(ptr uintptr) uintptr {
diff --git a/src/runtime/arch_arm64.go b/src/runtime/arch_arm64.go
index 4e798e36b..6d3c856cf 100644
--- a/src/runtime/arch_arm64.go
+++ b/src/runtime/arch_arm64.go
@@ -9,7 +9,12 @@ const deferExtraRegs = 0
 
 const callInstSize = 4 // "bl someFunction" is 4 bytes
 
-const linux_MAP_ANONYMOUS = 0x20
+const (
+	linux_MAP_ANONYMOUS = 0x20
+	linux_SIGBUS        = 7
+	linux_SIGILL        = 4
+	linux_SIGSEGV       = 11
+)
 
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
diff --git a/src/runtime/arch_mips.go b/src/runtime/arch_mips.go
index bfaf890ae..5a7d05c89 100644
--- a/src/runtime/arch_mips.go
+++ b/src/runtime/arch_mips.go
@@ -9,7 +9,12 @@ const deferExtraRegs = 0
 
 const callInstSize = 8 // "jal someFunc" is 4 bytes, plus a MIPS delay slot
 
-const linux_MAP_ANONYMOUS = 0x800
+const (
+	linux_MAP_ANONYMOUS = 0x800
+	linux_SIGBUS        = 10
+	linux_SIGILL        = 4
+	linux_SIGSEGV       = 11
+)
 
 // It appears that MIPS has a maximum alignment of 8 bytes.
 func align(ptr uintptr) uintptr {
diff --git a/src/runtime/arch_mipsle.go b/src/runtime/arch_mipsle.go
index b6bf7d516..498cf862b 100644
--- a/src/runtime/arch_mipsle.go
+++ b/src/runtime/arch_mipsle.go
@@ -9,7 +9,12 @@ const deferExtraRegs = 0
 
 const callInstSize = 8 // "jal someFunc" is 4 bytes, plus a MIPS delay slot
 
-const linux_MAP_ANONYMOUS = 0x800
+const (
+	linux_MAP_ANONYMOUS = 0x800
+	linux_SIGBUS        = 10
+	linux_SIGILL        = 4
+	linux_SIGSEGV       = 11
+)
 
 // It appears that MIPS has a maximum alignment of 8 bytes.
 func align(ptr uintptr) uintptr {
diff --git a/src/runtime/os_darwin.go b/src/runtime/os_darwin.go
index eeb192dda..9255fb90f 100644
--- a/src/runtime/os_darwin.go
+++ b/src/runtime/os_darwin.go
@@ -22,6 +22,14 @@ const (
 	clock_MONOTONIC_RAW = 4
 )
 
+// Source:
+// https://opensource.apple.com/source/xnu/xnu-7195.141.2/bsd/sys/signal.h.auto.html
+const (
+	sig_SIGBUS  = 10
+	sig_SIGILL  = 4
+	sig_SIGSEGV = 11
+)
+
 // https://opensource.apple.com/source/xnu/xnu-7195.141.2/EXTERNAL_HEADERS/mach-o/loader.h.auto.html
 type machHeader struct {
 	magic      uint32
diff --git a/src/runtime/os_linux.go b/src/runtime/os_linux.go
index 403f00246..df5870a2d 100644
--- a/src/runtime/os_linux.go
+++ b/src/runtime/os_linux.go
@@ -23,6 +23,12 @@ const (
 	clock_MONOTONIC_RAW = 4
 )
 
+const (
+	sig_SIGBUS  = linux_SIGBUS
+	sig_SIGILL  = linux_SIGILL
+	sig_SIGSEGV = linux_SIGSEGV
+)
+
 // For the definition of the various header structs, see:
 // https://refspecs.linuxfoundation.org/elf/elf.pdf
 // Also useful:
diff --git a/src/runtime/runtime_unix.c b/src/runtime/runtime_unix.c
new file mode 100644
index 000000000..79dd7ce91
--- /dev/null
+++ b/src/runtime/runtime_unix.c
@@ -0,0 +1,56 @@
+//go:build none
+
+// This file is included on Darwin and Linux (despite the //go:build line above).
+
+#define _GNU_SOURCE
+#define _XOPEN_SOURCE
+#include <signal.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <ucontext.h>
+#include <string.h>
+
+void tinygo_handle_fatal_signal(int sig, uintptr_t addr);
+
+static void signal_handler(int sig, siginfo_t *info, void *context) {
+	ucontext_t* uctx = context;
+	uintptr_t addr = 0;
+	#if __APPLE__
+		#if __arm64__
+			addr = uctx->uc_mcontext->__ss.__pc;
+		#elif __x86_64__
+			addr = uctx->uc_mcontext->__ss.__rip;
+		#else
+			#error unknown architecture
+		#endif
+	#elif __linux__
+		// Note: this can probably be simplified using the MC_PC macro in musl,
+		// but this works for now.
+		#if __arm__
+			addr = uctx->uc_mcontext.arm_pc;
+		#elif __i386__
+			addr = uctx->uc_mcontext.gregs[REG_EIP];
+		#elif __x86_64__
+			addr = uctx->uc_mcontext.gregs[REG_RIP];
+		#else // aarch64, mips, maybe others
+			addr = uctx->uc_mcontext.pc;
+		#endif
+	#else
+		#error unknown platform
+	#endif
+	tinygo_handle_fatal_signal(sig, addr);
+}
+
+void tinygo_register_fatal_signals(void) {
+	struct sigaction act = { 0 };
+	// SA_SIGINFO:   we want the 2 extra parameters
+	// SA_RESETHAND: only catch the signal once (the handler will re-raise the signal)
+	act.sa_flags = SA_SIGINFO | SA_RESETHAND;
+	act.sa_sigaction = &signal_handler;
+
+	// Register the signal handler for common issues. There are more signals,
+	// which can be added if needed.
+	sigaction(SIGBUS, &act, NULL);
+	sigaction(SIGILL, &act, NULL);
+	sigaction(SIGSEGV, &act, NULL);
+}
diff --git a/src/runtime/runtime_unix.go b/src/runtime/runtime_unix.go
index 8c5a42ff7..ba5d5a593 100644
--- a/src/runtime/runtime_unix.go
+++ b/src/runtime/runtime_unix.go
@@ -26,6 +26,9 @@ func abort()
 //export exit
 func exit(code int)
 
+//export raise
+func raise(sig int32)
+
 //export clock_gettime
 func libc_clock_gettime(clk_id int32, ts *timespec)
 
@@ -74,6 +77,10 @@ func main(argc int32, argv *unsafe.Pointer) int {
 	main_argc = argc
 	main_argv = argv
 
+	// Register some fatal signals, so that we can print slightly better error
+	// messages.
+	tinygo_register_fatal_signals()
+
 	// Obtain the initial stack pointer right before calling the run() function.
 	// The run function has been moved to a separate (non-inlined) function so
 	// that the correct stack pointer is read.
@@ -119,6 +126,50 @@ func runMain() {
 	run()
 }
 
+//export tinygo_register_fatal_signals
+func tinygo_register_fatal_signals()
+
+// Print fatal errors when they happen, including the instruction location.
+// With the particular formatting below, `tinygo run` can extract the location
+// where the signal happened and try to show the source location based on DWARF
+// information.
+//
+//export tinygo_handle_fatal_signal
+func tinygo_handle_fatal_signal(sig int32, addr uintptr) {
+	if panicStrategy() == panicStrategyTrap {
+		trap()
+	}
+
+	// Print signal including the faulting instruction.
+	if addr != 0 {
+		printstring("panic: runtime error at ")
+		printptr(addr)
+	} else {
+		printstring("panic: runtime error")
+	}
+	printstring(": caught signal ")
+	switch sig {
+	case sig_SIGBUS:
+		println("SIGBUS")
+	case sig_SIGILL:
+		println("SIGILL")
+	case sig_SIGSEGV:
+		println("SIGSEGV")
+	default:
+		println(sig)
+	}
+
+	// TODO: it might be interesting to also print the invalid address for
+	// SIGSEGV and SIGBUS.
+
+	// Do *not* abort here, instead raise the same signal again. The signal is
+	// registered with SA_RESETHAND which means it executes only once. So when
+	// we raise the signal again below, the signal isn't handled specially but
+	// is handled in the default way (probably exiting the process, maybe with a
+	// core dump).
+	raise(sig)
+}
+
 //go:extern environ
 var environ *unsafe.Pointer