On Sun, 2013-06-16 at 16:30 +1000, Erik de Castro Lopo wrote: > Been busy, but I'm back looking at this. > > David Laight wrote: > > > With a scratch register there are some two instruction sequences. > > Reusing the destination register something like: > > > > addis %r30,%r31,hi(.label - 1b) > > lwzx %r30,lo(.label - 1b)(%r30) > > > > I've managed to convert that into something gcc understands: > > addis 30, 31, (.label-(1b))@ha > lwz 30, (.label-(1b))@l(30) > > The "@l" is the equivalent of lo() and "@ha" is the sign extending > verions of hi(). Unfortunately, this code segfaults on executiion. > I suspect that is because I have used the LWZ instruction instead > of LWZX suggested by David.
No, lwz is the right instruction. The above should work, tried stepping it in something like gdb to see waht exactly is going on ? lwzx is a form that takes only registers (adds two registers to make the address to load from). lwz takes a register and an immediate offset. Cheers, Ben. > Unfortunately gcc doesn't accept LWZX which I found documented > here: > > > http://pds.twi.tudelft.nl/vakken/in101/labcourse/instruction-set/lwzx.html > > and seems to have LX as a synonym, but that instruction only seems > to work on registers, not on addresses as we have here. > > I'm actually beginning to have a better understanding of the code > and I've pulled out these snippets code code into a small assember > program I'm compiling with gcc and running under gdb. > > Cheers, > Erik _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
