CATCH_TRAP doesn't work well on ARM Macs

[stefanhaller]

Describe the bug
On ARM Macs ("Apple Silicon"), CATCH_TRAP does work correctly in that it does stop in the debugger. However, you can't single-step from there, or even continue; you are stuck at the same source line forever.

This can be fixed by using the instruction d43e0000 instead of the d4200000 that is used now. This instruction is generated by the __builtin_debugtrap() function, which is also available on i386 and x86_64 and generates the int $3 instruction there. So a simple fix looks like this (against the devel branch):

diff --git a/src/catch2/internal/catch_debugger.hpp b/src/catch2/internal/catch_debugger.hpp
index c300da72..e3b0a24b 100644
--- a/src/catch2/internal/catch_debugger.hpp
+++ b/src/catch2/internal/catch_debugger.hpp
@@ -16,11 +16,7 @@ namespace Catch {
 
 #ifdef CATCH_PLATFORM_MAC
 
-    #if defined(__i386__) || defined(__x86_64__)
-        #define CATCH_TRAP() __asm__("int $3\n" : : ) /* NOLINT */
-    #elif defined(__aarch64__)
-        #define CATCH_TRAP()  __asm__(".inst 0xd4200000")
-    #endif
+    #define CATCH_TRAP() __builtin_debugtrap()
 
 #elif defined(CATCH_PLATFORM_IPHONE)
 

Platform information:

• OS: macOS 12.3.1
• Compiler+version: Apple clang version 13.0.0 (clang-1300.0.29.30)
• Catch version: v2.13.9 and v3.0.0-preview5

[horenmar]

Is this universally supported? Quick look around the internet suggests that this is supported by some (most?) versions of Clang, but not e.g. GCC.

[stefanhaller]

You're right, it's clang-specific. I was fooled by this claim that it works universally, without reading the comments further down that debunk it. Sorry.

In that case, the fix would be just to replace 0xd4200000 with 0xd43e0000 in the existing code. (It would of course be possible to check __has_builtin(__builtin_debugtrap) and use it if available, and fall back to assembly if not, but it doesn't seem worth it.)

[horenmar]

Is this also an issue for the iphone configuration? It also uses 0xd4200000 for dbg break.