[Bug target/71767] Endless stream of warnings when using GCC with -Wa,-q and Clang Integrated Assembler

[noloader at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71767

--- Comment #8 from Jeffrey Walton <noloader at gmail dot com> ---
(In reply to Iain Sandoe from comment #7)
> (In reply to Dominique d'Humieres from comment #4)
> > I see the problem after having updated to Xcode 8.0. I am currently testing
> > the following patch
> 
> >  /* The .text section is generated in varasm.c  */
> >  DEF_SECTION (text_coal_section, SECTION_CODE|SECTION_NO_ANCHOR,
> > -	     ".section __TEXT,__textcoal_nt,coalesced,pure_instructions", 0)
> > +	     ".section __TEXT,__text,coalesced,pure_instructions", 0)
> 
> actually, we need to come up with a patch that simply emits the text/etc.
> section whenever it would have emitted the text_coal/etc. one.. So rather
> than adjusting section definitions - we need to change which ones are
> selected in config/darwin.c
> 
> .. but this should be conditional on a new enough linker to support it, or
> we will break support for folks on ancient systems.  Is this repeatable
> without xcode8?

Yes, it is repeatable with Xcode 8. Someone else mentioned they duplicatd with
it.

> I have some patches in progress to detect the linker features at
> configuration time,

be careful here. You use the new linker when -wa,-q is present. The new linker
is the one in Clang Integrated Assembler. You use the old Apple ld when -Wa,-q
is _not_present. Or maybe mor correctly, you just use ld.

> so that we don't need to rely on guessing from the host
> system version. 

I _think_ you can detect which linker at runtime with something like the
following:

IS_GAS := $(shell $(CXX) -xc -c /dev/null -Wa,-v -o/dev/null 2>&1 | $(EGREP) -c
"GNU assembler")

Now, ld returns the string "GNU assembler". Clang returns the string "clang:
error: unsupported argument '--version' to option 'Wa,'".

The LLVM folks may have fixed it in
https://llvm.org/bugs/show_bug.cgi?id=24200. A quick check with Clang-3.8 using
MacPort compiler shows its not fixed:

$ /opt/local/bin/clang-mp-3.8 -xc -c /dev/null -Wa,--version -o/dev/null 2>&1
clang: error: unsupported argument '--version' to option 'Wa,'

> If this is not detectable by a linker feature, them perhaps
> we can determine the earliest linker that can manage without the separate
> sections (most likely considerably older than the one from Xcode8).

I don't know about some of the other options available to you.

Maybe the "safety valve" should be another option? I'm already doing "-Wa,-q";
another `-Wa,-x` won't other me.

Jeff