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Re: discuss: How to print XMM registers on i386/x86-64

Michal Ludvig <> writes:

> Hi all,
> current gdb has a problem with printing xmm registers on i386/x86-64
> architectures. XMM regsters are of type builtin_type_v4sf. In 5.1.1
> the output of 'comand info registers xmm0' was as follows:
> xmm0           0x00102030405060708090a0b0c0d0e0f0
> Now in current mainline it's completely broken (with the same type):
> xmm0  {f = {0x0, 0x0, 0x0, 0x0}} \
>        {f = {5.82303983e-10, 2.77686634e+29, -1.16826016e-09, \
>         -5.56616044e+29}}
> If I change the type to builtin_type_v4si I get a more useful output:
> xmm0  {f = {0x30201000, 0x70605040, 0xb0a09080, 0xf0e0d0c0}} \
>        {f = {807407616, 1885360192, -1331654528, -253701952}}
> So my question is how to print it? We shouldn't treat XMM registers as
> 4xFP, because it can contain 1) two double precision floats, 2) four
> single precision floats, 3) from 16 bytes, 8 words, 4 double words, 2
> quadwords or 1 double quadword (128b).
> For now gcc won't store more than one FP variable into each register,
> ie. we don't need to convert all parts to float.
> I propose to provide an output like it was in 5.1 and create a new
> command for exploring these registers from different type's point of
> view. For example 'show register xmm0 dw' would print each quarter in
> a decimal form (dw stands for doubleword), while 'show register xmm0
> dfp' would print both halves of the register as double precision
> floats.

That's the way I would go.  I'm not sure whether I'd like to see "dw"
there but we should use some flag for this.  

My first thought was extending the print /FMT argument but I'm not
sure whether this works.

> We need a working XMM debugging on x86-64 arch, because there it is
> the default for FP. Thus I'd like to change the type of xmm registers
> to builtin_type_v4si for gdb-5.2 so that it would be at least somehow
> useful. In the current state it is not.
> What do you think about these propositions?

Thanks for looking into this!

 Andreas Jaeger
  SuSE Labs

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