On Tue, Oct 05, 2010 at 11:40:11PM +0200, Joakim Tjernlund wrote:
> yes, but this could be a new PIC mode that uses a new better
> PIC mode for everything. Especially one that doesn't require each function
> to calculate the GOT address in the function prologue(why is that so?)
The ppc32 ABI is old, much like x86. cf. x86 -O2 -fPIC (without
hidden pragma).
foo:
call __i686.get_pc_thunk.cx
addl $_GLOBAL_OFFSET_TABLE_, %ecx
pushl %ebp
movl %esp, %ebp
popl %ebp
movl y...@got(%ecx), %eax
movl x...@got(%ecx), %edx
movl (%eax), %eax
addl (%edx), %eax
ret
[snip]
__i686.get_pc_thunk.cx:
movl (%esp), %ecx
ret
The new ppc64 -mcmodel=medium support does give you pic access to
locals.
-fPIC -O2 without hidden
.LC0:
.tc x[TC],x <-- compiler managed GOT entries
.LC1:
.tc y[TC],y
[snip]
.L.foo:
addis 11,2,....@toc@ha
addis 9,2,....@toc@ha
ld 11,....@toc@l(11)
ld 9,....@toc@l(9)
lwz 3,0(11)
lwz 0,0(9)
add 3,3,0
extsw 3,3
blr
-fPIC -O2 with hidden pragma
.L.foo:
addis 11,2,x...@toc@ha
addis 9,2,y...@toc@ha
lwz 3,x...@toc@l(11) <-- TOC/GOT pointer relative
lwz 0,y...@toc@l(9)
add 3,3,0
extsw 3,3
blr
x...@toc is equivalent to @GOTOFF on other processors.
--
Alan Modra
Australia Development Lab, IBM
