Re: Setting an SSE register to a certain value

Re: Setting an SSE register to a certain value

[Eli Zaretskii]

> Date: Wed, 28 Dec 2005 09:15:45 +0100
> From: Guillaume POIRIER <poirierg@gmail.com>
> 
> > That is, try this:
> >
> >   set $xmm2.uint128 = 0x000000000000000000000000FFFFFFFF
> 
> Thanks you so much! That worked beautifully. I hope this information
> can be added to your documentation as this will probably come in handy
> to other people, don't you think? :-)

Yes, I've just added the following to the manual:

2005-12-28  Eli Zaretskii  <eliz@gnu.org>

	* gdb.texinfo (Registers): Describe how to refer to SSE and MMX
	registers and the likes.


Index: gdb/doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.302
diff -u -r1.302 gdb.texinfo
--- gdb/doc/gdb.texinfo	24 Dec 2005 15:28:44 -0000	1.302
+++ gdb/doc/gdb.texinfo	28 Dec 2005 20:04:30 -0000
@@ -6279,6 +6279,36 @@
 that makes sense for your program), but the @code{info registers} command
 prints the data in both formats.
 
+@cindex SSE registers (x86)
+@cindex MMX registers (x86)
+Some machines have special registers whose contents can be interpreted
+in several different ways.  For example, modern x86-based machines
+have SSE and MMX registers that can hold several values packed
+together in several different formats.  @value{GDBN} refers to such
+registers in @code{struct} notation:
+
+@smallexample
+(@value{GDBP}) print $xmm1
+$1 = @{
+  v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
+  v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
+  v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
+  v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
+  v4_int32 = @{0, 20657912, 11, 13@},
+  v2_int64 = @{88725056443645952, 55834574859@},
+  uint128 = 0x0000000d0000000b013b36f800000000
+@}
+@end smallexample
+
+@noindent
+To set values of such registers, you need to tell @value{GDBN} which
+view of the register you wish to change, as if you were assigning
+value to a @code{struct} member:
+
+@smallexample
+ (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
+@end smallexample
+
 Normally, register values are relative to the selected stack frame
 (@pxref{Selection, ,Selecting a frame}).  This means that you get the
 value that the register would contain if all stack frames farther in