Hi Arnd,
On Wed, Jan 26, 2022 at 1:26 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
On Wed, Jan 26, 2022 at 10:16 AM Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
On Wed, Jan 26, 2022 at 9:54 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
The code that causes this is drivers/net/ipa/ipa_mem.c:ipa_mem_valid():
DECLARE_BITMAP(regions, IPA_MEM_COUNT) = { };
...
for_each_clear_bit(mem_id, regions, IPA_MEM_COUNT) {
if (ipa_mem_id_required(ipa, mem_id))
dev_err(dev, "required memory region %u missing\n",
mem_id);
}
This only happens with gcc-8, not with gcc-9, so it might be a
compiler bug. I don't see anything wrong with c:ipa_mem_valid()
nor with m68k's find_first_zero_bit().
I don't see any problems about how this code uses bitmap API.
The m68k version of find_first_zero_bit() looks correct as well.
The trouble is with "enum ipa_mem_id mem_id;" which is an int, and the bitmap API requires unsigned long. I tried to fix this[1] at the source, but the maintainers want each[2] call site to fix it instead. :(
Sorry, I don't get it. "mem_id" is not used as the bitmap, "regions" is,
and the latter has the correct type?
I think you are right here, and even if it was an array of 'unsigned
int' instead
of 'unsigned long', this should not change the size of the object on
a 32-bit architecture.
Indeed, size matters not here.
I ran the preprocessed code through cvise[1], bisecting for a reduced
test case that fails on gcc-8 but succeeds on gcc-9. The reduced
case is still fairly complex, and it appears to only happen in the
presence of an inline asm. Narrowing down the compiler versions shows
that anything after gcc-9.2 does not warn, but 9.1 and earlier versions do,
which is further indication that it was probably a false-positive that got
fixed in gcc.
Thanks for investigating! So let's ignore this.
FTR, my gcc-9 is 9.4.0, i.e. >= 9.2.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
