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

[Elena Zannoni]

Andrew Cagney writes:
 > > Michal Ludvig <mludvig@suse.cz> 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}}
 > 
 > When you say broken, you mean the output or the values?
 > 
 > >> 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).
 > 
 > 
 > The idea behind the registers having struct/union types was to make it 
 > possible for the user to ``explore'' (and access) sub fields and the 
 > composite vis:
 > 
 > 	$xmm0.v4si[1]
 > 	$xmm0.v2di[0]
 > 
 > (don't quote me on the syntax).  It sounds like the current type isn't 
 > sufficient - a union of types is needed?
 > 
 > Can I suggest treating how ``info registers'' displays registers as a 
 > separate problem - the code is free to display the registers in what 
 > ever format it sees fit.
 > 
 > >> 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 think the full register contents should be displayed - we can't assume 
 > that the user is using GCC.
 > 
 > Ok, one MMX patch comming right up ...
 > 
 > Andrew
 > 
 > 

Another example to look at is the printing of the AltiVec registers.
The code for this is in rs6000-tdep.c.

Elena