Hi,
> > >> 'volatile' just doesn't really do what you think it should do. The
> > >> PowerPC architecture is too complicated w.r.t. ordering of reads and
> > >> writes. In other words, you can't trust it.
It's not sufficient on PowerPC.
It might be necessary, depending on the compiler's mood for moving stuff
out of loops.
Consider:
| unsigned int *foo = (unsigned int *)0x12345678;
| void bar(void) { while(*foo != 0) asm("eieio"); }
gcc 4.3.4 with -O3 compiles this to
00000000 <bar>:
0: 3d 20 00 00 lis r9,0
2: R_PPC_ADDR16_HA foo
4: 81 69 00 00 lwz r11,0(r9)
6: R_PPC_ADDR16_LO foo
8: 80 0b 00 00 lwz r0,0(r11)
c: 2f 80 00 00 cmpwi cr7,r0,0
10: 4d 9e 00 20 beqlr cr7
14: 7c 00 06 ac eieio
18: 7c 00 06 ac eieio
1c: 4b ff ff f8 b 14 <bar+0x14>
Making the target of foo volatile properly rechecks the condition on
each iteration.
OTOH my PPC box runs fine, so I'm probably missing something obvious.
Simon
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