Hi Steve,
I don't really have a strong opinion about whether NumFloatRegs should
be changed back to the old value or not. What you suggest might be
clearer though.
I think we should still keep this changeset even if we decide to change
NumFloatRegs. In my opinion, copying a non-flattened register file is
wrong since flattening can depend on register content which might not
have been copied yet.
//Andreas
On 2014-02-05 18:36, Steve Reinhardt wrote:
Hi Andreas,
Thanks for fixing the bug. Your fix is not what I expected though... based
on our last email exchange, I had myself convinced that we should change
NumFloatRegs back to the old value (-8 from where it is now), and then just
hack in the extra 8 needed to leave space for the stack aliases when
calculating Ctrl_Reg_Base.
I see how this fix also solves the problem, but it leaves us in the strange
situation of having 8 more regs in the float reg file than really exist,
which (I would guess) are only ever accessed when they are copied back and
forth in this function.
What do you think?
Steve
On Wed, Feb 5, 2014 at 5:05 AM, Andreas Sandberg <[email protected]>wrote:
changeset 32784c63de81 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=32784c63de81
description:
x86: Fix x87 state transfer bug
Changeset 7274310be1bb (isa: clean up register constants) increased
the value of NumFloatRegs, which triggered a bug in
X86ISA::copyRegs(). This bug is caused by the x87 stack being
copied
twice since register indexes past NUM_FLOATREGS are mapped into the
x87 stack relative to the top of the stack, which is undefined when
the copy takes place.
This changeset updates the copyRegs() function to use access
registers
using the non-flattening interface, which guarantees that
undesirable
register folding does not happen.
diffstat:
src/arch/x86/utility.cc | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diffs (20 lines):
diff -r 09507a45c701 -r 32784c63de81 src/arch/x86/utility.cc
--- a/src/arch/x86/utility.cc Sun Feb 02 16:37:35 2014 +0100
+++ b/src/arch/x86/utility.cc Wed Feb 05 14:08:13 2014 +0100
@@ -240,13 +240,13 @@
{
//copy int regs
for (int i = 0; i < NumIntRegs; ++i)
- dest->setIntReg(i, src->readIntReg(i));
+ dest->setIntRegFlat(i, src->readIntRegFlat(i));
//copy float regs
for (int i = 0; i < NumFloatRegs; ++i)
- dest->setFloatRegBits(i, src->readFloatRegBits(i));
+ dest->setFloatRegBitsFlat(i, src->readFloatRegBitsFlat(i));
//copy condition-code regs
for (int i = 0; i < NumCCRegs; ++i)
- dest->setCCReg(i, src->readCCReg(i));
+ dest->setCCRegFlat(i, src->readCCRegFlat(i));
copyMiscRegs(src, dest);
dest->pcState(src->pcState());
}
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