Re: [RFA] gdbtypes.[ch] rs6000-tdep.c--AltiVec regs types

[Elena Zannoni <ezannoni at redhat dot com>]

Michael Snyder writes:
 > Daniel Jacobowitz wrote:
 > > 
 > > On Fri, Jan 11, 2002 at 05:32:45PM -0500, Elena Zannoni wrote:
 > > >
 > > > This patch provides a builtin union type for the AltiVec registers,
 > > > so that the printing of such regs is a bit more enlightening, like:
 > > >
 > > >
 > > > (gdb) p $vr0
 > > > $2 = {uint128 = 0x00000064000000c80000012c00000190,
 > > >       v4sf = {f = {1.40129846e-43, 2.80259693e-43, 4.20389539e-43, 5.60519386e-43}},
 > > >       v4si = {f = {100, 200, 300, 400}},
 > > >       v8hi = {f = {0, 100, 0, 200, 0, 300, 0, 400}},
 > > >       v16qi = {f = "\0\0\0d\0\0\0È\0\0\001,\0\0\001\220"}}
 > > > (gdb) p $vr0.v4si
 > > > $3 = {f = {100, 200, 300, 400}}
 > > > (gdb) p $vr0.v4si.f[2]
 > > > $4 = 300
 > > > (gdb) p $vr0.v4si.f[2]=444
 > > > $5 = 444
 > > 
 > > Why is the .f necessary?  Why not make $vr0.v4si an array rather than
 > > struct type?
 > 
 > I know this is historical (it's been done the same way for other
 > targets), 
 > and I'm guessing it's because a struct type can be passed by value,
 > while
 > an array type is always passed by reference.  You want a type that can
 > be passed to a function.
 > 
 > I should know this (I've dealt with it before), but my 
 > memory cache is shrinking with age and misuse.  ;-(


Yes, I found an old ChangeLog entry about this, saying the following:

"The compiler needs to use a struct because arrays aren't assignable,
and the compiler and the debugger should agree."

Elena