[libunwind] Always use unwind tables in tests

[peter.smith]

Summary

For many targets setting -fno-exceptions will prevent unwinding tables from being generated for the test programs. As libunwind depends on the tables to unwind the stack several tests will fail.

This change always adds -funwind-tables so that even when -fno-exceptions is set unwind tables are generated. On x86_64 clang will add this option implicitly as the ABI requires it, I've tested this with Arm and AArch64.

This is an attempt at fixing pr33858 https://bugs.llvm.org/show_bug.cgi?id=33858. I'm not experienced in this area so there may well be better ways of doing this.

[jroelofs]

test/libunwind/test/config.py

46

I don't think that's correct. It should be:

if not self.get_lit_bool('enable_exceptions', True):
    self.cxx.compile_flags += ['-fno-exceptions', '-DLIBUNWIND_HAS_NO_EXCEPTIONS']

i.e: treat 'enable_exceptions' as True if it's not found, and only add the compile flags turning exceptions off when it's known to be False.

[peter.smith]

Yes you are correct, thanks for pointing that out. I had somewhat naively assumed the True and False was the test. I've updated the diff.

[peter.smith]

Has anyone had any more thoughts on this or is there a different approach that I can try to fix this pr?

[sdardis]

I can report that this patch clears two test failures for MIPS when D38110 is applied.

[rengolin]

Hi Peter,

This has been marked as a blocker to 5.0.1. I'm approving it in light of three facts:

1. Our long discussions from many angles have pointed us to this solution in particular
2. You have addressed @joerg's comments
3. If also fixes Mips errors, as stated by @sdardis

Please update PR33858 with the commit revision, so we can backport to the release_50 branch.

Thanks!

test/libunwind/test/config.py

class Configuration(LibcxxConfiguration):
 
     def configure_features(self):
         super(Configuration, self).configure_features()
         if not self.get_lit_bool('enable_exceptions', True):
             self.config.available_features.add('libcxxabi-no-exceptions')
 
     def configure_compile_flags(self):
         self.cxx.compile_flags += ['-DLIBUNWIND_NO_TIMER']
-        if self.get_lit_bool('enable_exceptions', True):
-            self.cxx.compile_flags += ['-funwind-tables']
-        else:
+        if self.get_lit_bool('enable_exceptions', False):
             self.cxx.compile_flags += ['-fno-exceptions', '-DLIBUNWIND_HAS_NO_EXCEPTIONS']
+        # Stack unwinding tests need unwinding tables and these are not
+        # generated by default on all Targets.
+        self.cxx.compile_flags += ['-funwind-tables']
         if not self.get_lit_bool('enable_threads', True):
             self.cxx.compile_flags += ['-D_LIBUNWIND_HAS_NO_THREADS']
             self.config.available_features.add('libunwind-no-threads')
         super(Configuration, self).configure_compile_flags()
 
     def configure_compile_flags_header_includes(self):
         self.configure_config_site_header()