https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81996
Segher Boessenkool <segher at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |segher at gcc dot gnu.org
Known to fail| |8.0
--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Hi!
(In reply to Sergei Trofimovich from comment #2)
> gcc master is slightly better here but is still inefficient in fPIC mode:
>
> gcc -O2 -fno-PIC:
>
> f:
> mflr 3
> blr
>
> gcc -O2 -fPIC:
>
> f:
> stwu 1,-16(1)
> mflr 0
> stw 0,20(1)
> stw 30,8(1)
> lwz 9,0(1)
> lwz 0,20(1)
> lwz 3,4(9)
> lwz 30,8(1)
> mtlr 0
> addi 1,1,16
> blr
This code looks fine. But it is *without* -fstack-protector-all, and with
it indeed a problem shows up:
===
f:
stwu 1,-48(1)
mflr 0
stw 0,52(1) # save at old r1+4
stw 30,40(1)
lwz 9,-28680(2)
stw 9,28(1)
li 9,0
lwz 9,32(1) # tries to get the old r1; but that is at r1+48 !
lwz 10,28(1)
lwz 8,-28680(2)
xor. 10,10,8
li 8,0
lwz 3,4(9) # and load from old r1+4
bne 0,.L5
lwz 0,52(1)
lwz 30,40(1)
addi 1,1,48
mtlr 0
blr
.L5:
bl __stack_chk_fail@plt
===
Confirmed. (Needs -m32).
