[libcxxabi] Disable calls to fprintf when building for baremetal targets in release mode

[rs]

Summary

We've been having issues with using libcxxabi and libunwind for baremetal targets because fprintf is dependent on io functions, this patch disable calls to fprintf when building for baremetal targets in release mode.

libunwind patch is here https://reviews.llvm.org/D30340

[jroelofs]

LGTM

[EricWF]

isn't this incorrect because config.h always defines LIBCXX_BAREMETAL?

[jroelofs]

In D30339#685888, @EricWF wrote:

isn't this incorrect because config.h always defines LIBCXX_BAREMETAL?

Oh, right, it needs to be:

#if !LIBCXXABI_BAREMETAL || !defined(NDEBUG)

[rmaprath]

Perhaps change config.h and remove the definition there and adjust other places accordingly?

The current form is very easy to trip over.

[jroelofs]

In D30339#685919, @rmaprath wrote:

Perhaps change config.h and remove the definition there and adjust other places accordingly?

The current form is very easy to trip over.

Eric's point is that LIBCXXABI_BAREMETAL is a 0/1 flag, not a defined/not-defined flag. Please don't change from one form to the other... it's disruptive to build systems.

[rs]

Ah sorry for the mistake. Fix is here https://reviews.llvm.org/D30343

[EricWF]

In D30339#685921, @jroelofs wrote:

In D30339#685919, @rmaprath wrote:

Perhaps change config.h and remove the definition there and adjust other places accordingly?

The current form is very easy to trip over.

Eric's point is that LIBCXXABI_BAREMETAL is a 0/1 flag, not a defined/not-defined flag. Please don't change from one form to the other... it's disruptive to build systems.

I actually think it's better to maintain consistency between libc++ and libc++abi. And libc++ never uses 0/1 flags. So I would rather see a fix in config.h.

Frankly I don't care that it is disruptive to build systems unless it's the build system owned by LLVM.

src/abort_message.cpp

 #       include <CrashReporterClient.h>
 #   endif
 #endif
 
 __attribute__((visibility("hidden"), noreturn))
 void abort_message(const char* format, ...)
 {
     // write message to stderr
+#if !defined(NDEBUG) && !defined(LIBCXXABI_BAREMETAL)
 #ifdef __APPLE__
     fprintf(stderr, "libc++abi.dylib: ");
 #endif
     va_list list;
     va_start(list, format);
     vfprintf(stderr, format, list);
     va_end(list);
     fprintf(stderr, "\n");
+#endif
 
 #if defined(__APPLE__) && defined(HAVE_CRASHREPORTERCLIENT_H)
     // record message in crash report
     char* buffer;
     va_list list2;
     va_start(list2, format);
     vasprintf(&buffer, format, list2);
     va_end(list2);