AltiVec aware ptrace for Linux

[Franz Sirl]

At 15:27 07.09.2001, Edwin Robert Tisdale wrote:

>Paul Mackerras wrote:
>
> > 1. Make a unified diff listing rather than the old-style diff.
> >
> > 2. Your diff is backwards, it shows your new stuff as being deleted.
> >    Do the diff as "diff -u old new".
> >
> > 3. Don't take out the "addr = addr >> 2;" lines.
> >    I know the comment says "temporary hack"
> >    but you don't want to believe everything you read. :)
> >    In fact, a lot of existing software relies on
> >    the argument to PTRACE_PEEK/POKEUSR
> >    being an offset into a notional structure rather than an index
> >    and your change would introduce a significant change
> >    to existing behaviour which would break applications.
> >    Note that >> 2 divides by 4, not 2
> >    as you seemed to think in a previous message.
> >
> > 4. Send the patch to me (paulus at samba.org, the PPC/Linux maintainer)
> >    and to the linuxppc-dev at lists.linuxppc.org list.
>
>/usr/src/linux-2.2.19/arch/ppc/kernel$ diff -u ptrace.cold ptrace.c
>--- ptrace.cold Sun Mar 25 08:31:49 2001
>+++ ptrace.c Fri Sep  7 07:00:43 2001
>@@ -415,19 +415,26 @@
>     unsigned long tmp;
>
>     ret = -EIO;
>-   if ((addr & 3) || addr < 0 || addr > (PT_FPSCR << 2))
>+   if ((addr & 3))
>      goto out;
>
>     tmp = 0;  /* Default return condition */
>-   addr = addr >> 2; /* temporary hack. */
>-   if (addr < PT_FPR0) {
>+   addr >>= 2;
>+   if (PT_R0 <= addr && addr <= PT_MQ) {
>      tmp = get_reg(child, addr);
>     }
>-   else if (addr >= PT_FPR0 && addr <= PT_FPSCR) {
>+   else if (PT_FPR0 <= addr && addr <= PT_FPSCR) {
>      if (child->tss.regs->msr & MSR_FP)
>       giveup_fpu(child);
>      tmp = ((long *)child->tss.fpr)[addr - PT_FPR0];
>     }
>+#ifdef CONFIG_ALTIVEC
>+   else if (PT_VR0 <= addr && addr <= PT_VRSAVE) {
>+    if (child->tss.regs->msr & MSR_VEC)
>+     giveup_altivec(child);
>+    tmp = ((long *)child->tss.vr)[addr - PT_VR0];
>+   }
>+#endif /* CONFIG_ALTIVEC */
>     else
>      goto out;
>     ret = put_user(tmp, (unsigned long *) data);
>@@ -444,26 +451,29 @@
>
>    case PTRACE_POKEUSR: /* write the word at location addr in the USER
> area */
>     ret = -EIO;
>-   if ((addr & 3) || addr < 0 || addr >= ((PT_FPR0 + 64) << 2))
>+   if ((addr & 3) || PT_ORIG_R3 == addr)
>      goto out;
>
>-   addr = addr >> 2; /* temporary hack. */
>-
>-   if (addr == PT_ORIG_R3)
>-    goto out;
>-   if (addr < PT_FPR0) {
>+   addr >>= 2;
>+   if (PT_FPR0 <= addr && addr <= PT_FPSCR) {
>      if (put_reg(child, addr, data))
>       goto out;
>      ret = 0;
>-    goto out;
>     }
>-   if (addr >= PT_FPR0 && addr < PT_FPR0 + 64) {
>+   else if (PT_FPR0 <= addr && addr <= PT_FPSRC) {
>      if (child->tss.regs->msr & MSR_FP)
>       giveup_fpu(child);
>      ((long *)child->tss.fpr)[addr - PT_FPR0] = data;     ret = 0;
>-    goto out;
>     }
>+#ifdef CONFIG_ALTIVEC
>+   else if (PT_VR0 <= addr && addr <= PT_VRSAVE) {
>+    if (child->tss.regs->msr & MSR_VEC)
>+     giveup_altivec(child);
>+    ((long *)child->tss.vr)[addr - PT_VR0] = data;
>+    ret = 0;
>+   }
>+#endif /* CONFIG_ALTIVEC */
>     goto out;
>
>    case PTRACE_SYSCALL: /* continue and stop at next (return from) syscall */
>
>/usr/src/linux-2.2.19/include/asm$ diff -u ptrace.hold ptrace.h
>--- ptrace.hold Sun Mar 25 08:31:08 2001
>+++ ptrace.h Thu Sep  6 17:13:12 2001
>@@ -97,5 +97,12 @@
>  #define PT_FPR31 (PT_FPR0 + 2*31)
>  #define PT_FPSCR (PT_FPR0 + 2*32 + 1)
>
>+#ifdef CONFIG_ALTIVEC
>+#define PT_VR0 128
>+#define PT_VR31 (PT_VR0 + 4*31)
>+#define PT_VRCR (PT_VR0 + 4*32)
>+#define PT_VRSAVE (PT_VR0 + 4*33 + 1)
>+#endif /* CONFIG_ALTIVEC */
>+
>  #endif
>
>

Well, since nobody else dares to comment, here some of mine (and I cc'ed
Daniel because he dealt with that earlier I think):

- is it really a good idea to stuff this into PEEK/POKEUSR?
- how are userspace apps supposed to detect what version of data
PEEK/POKEUSR give back?
- how well does this work with a possible AltiVec2 engine with different
register sizes/layout?
- wouldn't it be better to introduce PTRACE_[SG]ETVR[2]REGS, which would be
able to return something like ENOSYS if AltiVec[2] is not enabled?

Franz.


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