Greg's off-line this week but it'd be worth checking with him about how the
names on Darwin were chosen.
I don't know if it's that important to maintain the exact same names for these
types of registers. The thread context structure (defined in the system header
files) defines these as
_STRUCT_FP_CONTROL __fpu_fcw; /* x87 FPU control word
*/
_STRUCT_FP_STATUS __fpu_fsw; /* x87 FPU status word
*/
__uint8_t __fpu_ftw; /* x87 FPU tag word */
__uint8_t __fpu_rsrv1; /* reserved */
__uint16_t __fpu_fop; /* x87 FPU Opcode */
/* x87 FPU Instruction Pointer */
__uint32_t __fpu_ip; /* offset */
__uint16_t __fpu_cs; /* Selector */
__uint16_t __fpu_rsrv2; /* reserved */
/* x87 FPU Instruction Operand(Data) Pointer */
__uint32_t __fpu_dp; /* offset */
__uint16_t __fpu_ds; /* Selector */
The actual behavior on a Darwin system is,
(lldb) reg read -a
[...]
Floating Point Registers:
fctrl = 0x037f
fstat = 0x0020
ftag = 0x00
fop = 0x0000
fioff = 0x8a114262
fiseg = 0x002b
fooff = 0x8a14bf30
foseg = 0x0000
mxcsr = 0x00001fa3
mxcsrmask = 0x0000ffff
stmm0 = {0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xff 0xff}
[...]
(lldb) reg read ip
error: Invalid register name 'ip'.
(lldb) reg read fpu_ip
error: Invalid register name 'fpu_ip'.
(lldb) reg read fioff
fioff = 0x8a114262
(lldb)
On Aug 7, 2013, at 11:43 AM, Richard Mitton <[email protected]> wrote:
> Exactly, displaying an 'ip' register which is not the instruction pointer is
> very unhelpful.
>
> The existing register names are currently different on posix-vs-Darwin
> anyway, so there shouldn't be any harm in making the change now. I think it's
> "fioff" on Darwin. It uses different display names vs. the internal variable
> names.
>
> I agree that it would be nice to make it consistent everywhere. Personally
> I'm in favor of it matching the Intel names as closely as possible. I'm
> slightly puzzled by how many places in the codebase (re)define the register
> sets, it seems like making changes like this may not be straightforward.
>
> Richard Mitton
> [email protected]
>
> On 08/07/2013 09:12 AM, Daniel Malea wrote:
>> To clarify the original problem this patch addresses (Richard correct me
>> if I'm wrong) the result of a user doing "register read ip" is that they
>> would see the floating point register instead of the instruction pointer.
>>
>> This change makes the register names on POSIX platforms diverge from the
>> Mac OS X ones.. Specifically, in the darwin plugins, the register in
>> question is still called "ip".
>>
>> At the very least, this implies we should change TestRegisters.py as well
>> (in its current form, it crashes) but i'm not sure that change is ideal as
>> we'd have to use different names for the same hardware on different
>> platforms.
>>
>> My gut feeling is we should probably keep register names consistent across
>> platforms... so making this change to the POSIX side might require a
>> corresponding change on the Darwin side -- maybe someone from Apple can
>> chime in on the merits?
>>
>> http://llvm-reviews.chandlerc.com/D1307
>
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