[lttng-dev] Babeltrace2 - compilation error with intel18

[Simon Marchi]

On 2020-03-23 12:56 p.m., Rocky Dunlap wrote:
> Simon,
> 
> Success!  This change worked and I was able to build and install with icc.  Thank you!

Ok, thanks.  Out of curiosity, did run a "make check"?  That would validate that
the Python bindings (and everything else) works properly.

> I still get a lot of warnings during the build (see below) which seems like configure should work these out ahead of time.  They are easy enough to ignore, but if support for intel is added, it would be nice to have these cleaned up.  For what it's worth, adding support for additional compilers in my experience has greatly improved the quality of library code - it tends to snuff out those bugs that are hard to find on a single compiler.  

I agree, that's why we want to keep babeltrace building with clang (on top of having to
support macOS, on which clang is the default compiler).

We use the AX_APPEND_COMPILE_FLAGS autoconf macro [1] to determine which warning flags
the current compiler supports.  This calls the compiler with each flag individually
to see if the compiler supports that flag.  This requires that the compiler errors
out when passed an invalid flag.  Currently, it looks like icc emits a warning, but still
returns exit code 0 when passed an invalid flag, so we end up enabling all of them.  Try
to check in config.log to see what happens currently.  For example here are the test
results for two flags, one supported and one not supported by clang:

4625 configure:17825: checking whether C compiler accepts -Winit-self
4626 configure:17844: ccache clang -c -gdwarf-5 -g3 -O2 -fsanitize=address -Werror -Winit-self  conftest.c >&5
4627 configure:17844: $? = 0
4628 configure:17853: result: yes
4629 configure:17869: : WARN_CFLAGS="$WARN_CFLAGS"
4630 configure:17872: $? = 0
4631 configure:17825: checking whether C compiler accepts -Wduplicated-cond
4632 configure:17844: ccache clang -c -gdwarf-5 -g3 -O2 -fsanitize=address -Werror -Wduplicated-cond  conftest.c >&5
4633 error: unknown warning option '-Wduplicated-cond'; did you mean '-Wduplicate-enum'? [-Werror,-Wunknown-warning-option]
4634 configure:17844: $? = 1

If you can come up with the right incantation to make that work well with icc, we
can modify how we call the macro or modify the macro itself (sending a patch to
the upstream, Autoconf Archive).

[1] https://www.gnu.org/software/autoconf-archive/ax_append_compile_flags.html

> If you decide to merge this in, a release patch 2.0.3 would certainly be helpful as well!

Things have started to diverge a bit between master and the 2.0 branch, I'm not sure if we'll
be able to backport that, we'll see.

Simon
>