lto: lto-opts fixes [PR119625]

lto: lto-opts fixes [PR119625]

I can reproduce a really weird error in our distro i686 trunk gcc
(but haven't managed to reproduce it with vanilla trunk yet).
echo 'void foo (void) {}' > a.c; gcc -O2 -flto=auto -m32 -march=i686 -ffat-lto-objects -fhardened -o a.o -c a.c; gcc -O2 -flto=auto -m32 -march=i686 -r -o a.lo a.o
lto1: fatal error: open  failed: No such file or directory
compilation terminated.
lto-wrapper: fatal error: gcc returned 1 exit status
The error is because
cat ./a.lo.lto.o-args.0
""
a.o
My suspicion is that this "" in there is caused by weird .gnu.lto_.opts
section content during
gcc -O2 -flto=auto -m32 -march=i686 -ffat-lto-objects -fhardened -S -o a.s -c a.c
compilation (and I can reproduce that one with vanilla trunk).
The above results in
        .section        .gnu.lto_.opts,"e",@progbits
        .string "'-fno-openmp' '-fno-openacc' '-fPIC' '' '-m32' '-march=i686' '-O2' '-flto=auto' '-ffat-lto-objects'"
There are two weird things, one (IMHO the cause of the "" later on) is
the '' part, I think it comes from lto_write_options doing
append_to_collect_gcc_options (&temporary_obstack, &first_p, "");
IMHO it shouldn't call append_to_collect_gcc_options at all for that case.

The -fhardened option causes global_options.x_flag_cf_protection
to be set to CF_FULL and later on the backend option processing
sets it to CF_FULL | CF_SET (i.e. 7, a value not handled in
lto_write_options).

The following patch fixes it by not emitting anything there if
flag_cf_protection is one of the unhandled values.

Perhaps it could incrementally use
switch (global_options.x_flag_cf_protection & ~CF_SET)
instead, dunno.

And the other problem is that the -fPIC in there is really weird.
Our distro compiler or vanilla configured trunk certainly doesn't
default to -fPIC and -fhardened uses -fPIE when
-fPIC/-fpic/-fno-pie/-fno-pic is not specified, so I was expecting
-fPIE in there.
The thing is that the -fpie option causes setting of both
global_options.x_flag_pi{c,e} to 1, -fPIE both to 2:
      /* If -fPIE or -fpie is used, turn on PIC.  */
      if (opts->x_flag_pie)
        opts->x_flag_pic = opts->x_flag_pie;
      else if (opts->x_flag_pic == -1)
        opts->x_flag_pic = 0;
      if (opts->x_flag_pic && !opts->x_flag_pie)
        opts->x_flag_shlib = 1;
so checking first for flag_pic == 2 and then flag_pic == 1
and only afterwards for flag_pie means we never print
-fPIE/-fpie.

Or do you want something further (like
switch (global_options.x_flag_cf_protection & ~CF_SET)
)?

2025-04-04  Jakub Jelinek  <jakub@redhat.com>

	PR lto/119625
	* lto-opts.cc (lto_write_options): If neither flag_pic nor
	flag_pie are set, check first for flag_pie and only later
	for flag_pic rather than the other way around, use a temporary
	variable.  If flag_cf_protection is not set, don't append anything
	if flag_cf_protection is none of CF_{NONE,FULL,BRANCH,RETURN} and
	use a temporary variable.