https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98692
--- Comment #16 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Mark Wielaard from comment #13)
> ==25741== Use of uninitialised value of size 8
> ==25741== at 0x10000504: main (pr9862.C:16)
r4 is argv here
> 0x00000000100004f0 <+16>: ld r3,0(r4)
r3 = argv[0];
> 0x00000000100004f4 <+20>: mr r31,r4
r31 = argv; // because we need it after the call, save it in a non-volatile reg
> 0x00000000100004f8 <+24>: std r0,16(r1)
> 0x00000000100004fc <+28>: stdu r1,-48(r1)
> 0x0000000010000500 <+32>: bl 0x100006b4 <isVariable(char*)+8>
The call; after this we have to load argv[0] again, the called function might
have changed it.
> 0x0000000010000504 <+36>: ld r3,0(r31)
r3 = argv[0];
So it is funny that the exact same insn four insns earlier (in the program
text)
worked fine, but this one fails.
The ABI says (taken from the ELFv1 ABI, the ELFv2 doc is not nice for
copy/paste):
Here is a sample implementation of _savegpr0_N and _restgpr0_N.
_savegpr0_14: std r14,-144(r1)
_savegpr0_15: std r15,-136(r1)
_savegpr0_16: std r16,-128(r1)
_savegpr0_17: std r17,-120(r1)
_savegpr0_18: std r18,-112(r1)
_savegpr0_19: std r19,-104(r1)
_savegpr0_20: std r20,-96(r1)
_savegpr0_21: std r21,-88(r1)
_savegpr0_22: std r22,-80(r1)
_savegpr0_23: std r23,-72(r1)
_savegpr0_24: std r24,-64(r1)
_savegpr0_25: std r25,-56(r1)
_savegpr0_26: std r26,-48(r1)
_savegpr0_27: std r27,-40(r1)
_savegpr0_28: std r28,-32(r1)
_savegpr0_29: std r29,-24(r1)
_savegpr0_30: std r30,-16(r1)
_savegpr0_31: std r31,-8(r1)
std r0, 16(r1)
blr
_restgpr0_14: ld r14,-144(r1)
_restgpr0_15: ld r15,-136(r1)
_restgpr0_16: ld r16,-128(r1)
_restgpr0_17: ld r17,-120(r1)
_restgpr0_18: ld r18,-112(r1)
_restgpr0_19: ld r19,-104(r1)
_restgpr0_20: ld r20,-96(r1)
_restgpr0_21: ld r21,-88(r1)
_restgpr0_22: ld r22,-80(r1)
_restgpr0_23: ld r23,-72(r1)
_restgpr0_24: ld r24,-64(r1)
_restgpr0_25: ld r25,-56(r1)
_restgpr0_26: ld r26,-48(r1)
_restgpr0_27: ld r27,-40(r1)
_restgpr0_28: ld r28,-32(r1)
_restgpr0_29: ld r0, 16(r1)
ld r29,-24(r1)
mtlr r0
ld r30,-16(r1)
ld r31,-8(r1)
blr
_restgpr0_30: ld r30,-16(r1)
_restgpr0_31: ld r0, 16(r1)
ld r31,-8(r1)
mtlr r0
blr
So this is one function with many entry points you could say. Maybe that is
what confused valgrind?
