Re: gcc possibly generating invalid assembler

[Wouter Verhelst <wouter@debian.org>]

On Thu, Apr 13, 2017 at 01:08:59PM +0200, John Paul Adrian Glaubitz wrote:
> Hi!
> 
> I have unsuccessfully been trying to build liburcu on Debian/m68k. After
> adding "m68k" as a detected architecture in configure.ac, the build
> fails with the assembler generating syntax error messages [1]:
> 
> gcc -DHAVE_CONFIG_H -I. -I../.. -I../../urcu   -Wdate-time -D_FORTIFY_SOURCE=2 -I../.. -I../.. -I../../tests/common -g -g -O2
> -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -pthread -c -o test_urcu_defer.o test_urcu_defer.c
> /tmp/ccXHVXOc.s: Assembler messages:
> /tmp/ccXHVXOc.s:312: Error: syntax error -- statement `add.l %d1,nr_writes@TLSLE+4(%a0)' ignored
> /tmp/ccXHVXOc.s:440: Error: syntax error -- statement `add.l %d1,nr_writes@TLSLE+4(%a0)' ignored

Interesting.

> Since the source code file in question doesn't contain any m68k inline
> assembly, I would suspect this to be a problem with the code generated
> by gcc.
> 
> Any suggestions?

I wanted to have a closer look, so added a line saying "[m68k],
[ARCHTYPE="gcc"]," to the AS_CASE statement in configure.ac (which I'm
assuming is what you did, too; next time it would be useful if you
shared your patches ;-) ). Then I ran make until it encountered the
above error.

Then I ran 'make CFLAGS=-save-temps' to see whether it perhaps did add
some inline assembly somewhere but you missed the #include and this time
it... worked?

Not sure what's going on here.

-- 
< ron> I mean, the main *practical* problem with C++, is there's like a dozen
       people in the world who think they really understand all of its rules,
       and pretty much all of them are just lying to themselves too.
 -- #debian-devel, OFTC, 2016-02-12