[RFA] Tweak in skip_prologue for rs6000

[RFA] Tweak in skip_prologue for rs6000

[Michael Snyder]

Kevin, 

If I'm right, this will prevent saving lr_offset twice.  It looks like the 
existing code intends to invalidate lr_reg, but setting it to zero is not
an invalid value.

Probably the same is true for cr_reg and cr_offset...

Michael

2004-11-10  msnyder  <msnyder@redhat.com>

 * rs6000-tdep.c (skip_prologue): After saving lr_offset, 
 must invalidate lr_reg (so we don't try to save it again).  

Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.230
diff -p -r1.230 rs6000-tdep.c
*** rs6000-tdep.c 13 Oct 2004 16:38:22 -0000 1.230
--- rs6000-tdep.c 11 Nov 2004 01:04:40 -0000
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 981,987 ****
     continue;
  
   }
!       else if (lr_reg != -1 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (lr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
--- 981,987 ----
     continue;
  
   }
!       else if (lr_reg >= 0 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (lr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 991,997 ****
   { /* where Rx == lr */
     fdata->lr_offset = offset;
     fdata->nosavedpc = 0;
!    lr_reg = 0;
     if ((op & 0xfc000003) == 0xf8000000 || /* std */
         (op & 0xfc000000) == 0x90000000)  /* stw */
       {
--- 991,999 ----
   { /* where Rx == lr */
     fdata->lr_offset = offset;
     fdata->nosavedpc = 0;
!    /* Invalidate lr_reg, but don't set it to -1.
!       That would mean that it had never been set.  */
!    lr_reg = -2;
     if ((op & 0xfc000003) == 0xf8000000 || /* std */
         (op & 0xfc000000) == 0x90000000)  /* stw */
       {

Re: [RFA] Tweak in skip_prologue for rs6000

[Kevin Buettner]

On Wed, 10 Nov 2004 17:11:21 -0800
"Michael Snyder" <michsnyd@cisco.com> wrote:

> If I'm right, this will prevent saving lr_offset twice.  It looks like the 
> existing code intends to invalidate lr_reg, but setting it to zero is not
> an invalid value.

Yes, I agree with your analysis.  Setting lr_reg to 0 will cause a
match whenever doing a st[dw]{,u} r0, NUM(r1).  While this is okay
if the zero value comes from the mflr case, it is definitely not okay
in the lr_reg invalidation code.

> Probably the same is true for cr_reg and cr_offset...

Yes, it appears so.  Would you mind making the same fix for these? 
Consider such a patch to be preapproved.

>  * rs6000-tdep.c (skip_prologue): After saving lr_offset, 
>  must invalidate lr_reg (so we don't try to save it again).  

Definitely okay.

Thanks for fixing this,

Kevin

Re: [RFA] Tweak in skip_prologue for rs6000

[Michael Snyder]

"Kevin Buettner" <kevinb@redhat.com> wrote:

> On Wed, 10 Nov 2004 17:11:21 -0800
> "Michael Snyder" <michsnyd@cisco.com> wrote:
> 
>> If I'm right, this will prevent saving lr_offset twice.  It looks like the 
>> existing code intends to invalidate lr_reg, but setting it to zero is not
>> an invalid value.
> 
> Yes, I agree with your analysis.  Setting lr_reg to 0 will cause a
> match whenever doing a st[dw]{,u} r0, NUM(r1).  While this is okay
> if the zero value comes from the mflr case, it is definitely not okay
> in the lr_reg invalidation code.
> 
>> Probably the same is true for cr_reg and cr_offset...
> 
> Yes, it appears so.  Would you mind making the same fix for these? 
> Consider such a patch to be preapproved.

OK, committed.  Revised version attached below.  
Thanks Kevin.  Oh, and thanks to Wendy Peikes of Cisco
for her help in tracking this down.

2004-11-10  msnyder  <msnyder@redhat.com>

 * rs6000-tdep.c (skip_prologue): After saving lr_offset, 
 must invalidate lr_reg (so we don't try to save it again).  
 Ditto for cr_offset and cr_reg.

Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.230
diff -p -r1.230 rs6000-tdep.c
*** rs6000-tdep.c 13 Oct 2004 16:38:22 -0000 1.230
--- rs6000-tdep.c 11 Nov 2004 19:14:29 -0000
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 981,987 ****
     continue;
  
   }
!       else if (lr_reg != -1 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (lr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
--- 981,987 ----
     continue;
  
   }
!       else if (lr_reg >= 0 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (lr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 991,997 ****
   { /* where Rx == lr */
     fdata->lr_offset = offset;
     fdata->nosavedpc = 0;
!    lr_reg = 0;
     if ((op & 0xfc000003) == 0xf8000000 || /* std */
         (op & 0xfc000000) == 0x90000000)  /* stw */
       {
--- 991,999 ----
   { /* where Rx == lr */
     fdata->lr_offset = offset;
     fdata->nosavedpc = 0;
!    /* Invalidate lr_reg, but don't set it to -1.
!       That would mean that it had never been set.  */
!    lr_reg = -2;
     if ((op & 0xfc000003) == 0xf8000000 || /* std */
         (op & 0xfc000000) == 0x90000000)  /* stw */
       {
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 1001,1007 ****
     continue;
  
   }
!       else if (cr_reg != -1 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (cr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
--- 1003,1009 ----
     continue;
  
   }
!       else if (cr_reg >= 0 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (cr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 1010,1016 ****
    ((op & 0xffff0000) == (cr_reg | 0x94010000))))
   { /* where Rx == cr */
     fdata->cr_offset = offset;
!    cr_reg = 0;
     if ((op & 0xfc000003) == 0xf8000000 ||
         (op & 0xfc000000) == 0x90000000)
       {
--- 1012,1020 ----
    ((op & 0xffff0000) == (cr_reg | 0x94010000))))
   { /* where Rx == cr */
     fdata->cr_offset = offset;
!    /* Invalidate cr_reg, but don't set it to -1.
!       That would mean that it had never been set.  */
!    cr_reg = -2;
     if ((op & 0xfc000003) == 0xf8000000 ||
         (op & 0xfc000000) == 0x90000000)
       {