[Bug target/23774] New: dealloc of dynamic stack space breaks backchain

[Bug target/23774] New: dealloc of dynamic stack space breaks backchain

[amodra at bigpond dot net dot au]

The following compiled with -m32 -O2 -S

void badFunc (int size)
{ 
  char temp[size];
  temp[size-1] = '\0';
};

gives

badFunc:
        mflr 0
        stwu 1,-16(1)
        stw 0,20(1)
        addi 0,3,30
        lwz 9,0(1)
        mr 11,1
        stw 31,12(1)
        mr 31,1
        rlwinm 0,0,0,0,27
        neg 0,0
        stwux 9,1,0
        li 9,0
        addi 0,1,23
        rlwinm 0,0,0,0,27
        add 3,3,0
        stb 9,-1(3)      <- old backchain possibly overwritten
        nop
        nop
        nop
        lwz 0,0(1)
        mr 1,11          <- adjust stack, backchain possibly invalid!
        stw 0,0(1)       <- write backchain
        nop
        lwz 11,0(1)
        lwz 0,4(11)
        lwz 31,-4(11)
        mr 1,11
        mtlr 0
        blr

This testcase also shows
a) excess allocation of dynamic stack space,
b) needless alignment of dynamic stack space,
c) poor epilogue code, with unnecesary stack adjustments.

-- 
           Summary: dealloc of dynamic stack space breaks backchain
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: amodra at bigpond dot net dot au
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: powerpc-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774

[Bug target/23774] dealloc of dynamic stack space breaks backchain

[amodra at bigpond dot net dot au]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.0.2 4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774

[Bug target/23774] dealloc of dynamic stack space breaks backchain

[amodra at bigpond dot net dot au]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |amodra at bigpond dot net
                   |dot org                     |dot au
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-09-08 03:22:26
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774

[Bug target/23774] dealloc of dynamic stack space breaks backchain

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-09 03:14 -------
This causes wrong code in a way and also causes wrong debugging too as the backchain is broken.


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code, wrong-debug


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774

[Bug target/23774] dealloc of dynamic stack space breaks backchain

[amodra at bigpond dot net dot au]

------- Additional Comments From amodra at bigpond dot net dot au  2005-09-13 00:33 -------
The same thing happens with __builtin_longjmp, eg. extracted from
gcc.c-torture/execute/builtins/lib/chk.c

void __attribute__((noreturn))
__chk_fail (void)
{
  if (chk_fail_allowed)
    __builtin_longjmp (chk_fail_buf, 1);
  abort ();
}

generates

__chk_fail:
	stwu 1,-16(1)
	mflr 0
	stw 31,12(1)
	stw 0,20(1)
	mr 31,1
	lis 9,chk_fail_allowed@ha
	lwz 0,chk_fail_allowed@l(9)
	cmpwi 7,0,0
	beq- 7,.L133
	lis 11,chk_fail_buf@ha
	la 9,chk_fail_buf@l(11)
	lwz 0,4(9)
	mtctr 0
	lwz 31,chk_fail_buf@l(11)
	lwz 0,8(9)
	lwz 1,12(9)            <- stack adjusted
	stw 0,0(1)             <- backchain written
	bctr


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774

[Bug target/23774] dealloc of dynamic stack space breaks backchain

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-09-13 02:01 -------
Subject: Bug 23774

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	amodra@gcc.gnu.org	2005-09-13 02:01:04

Modified files:
	gcc            : ChangeLog 
	gcc/config/rs6000: rs6000.md 

Log message:
	PR target/23774
	* config/rs6000/rs6000.md (restore_stack_block): Write the backchain
	word before changing the stack pointer.	 Use gen_frame_mem for MEMs.
	Use UNSPEC_TIE to prevent insn scheduling reordering the insns.
	(restore_stack_nonlocal): Likewise.
	(save_stack_nonlocal): Use template to emit insns, and gen_frame_mem.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.9942&r2=2.9943
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/config/rs6000/rs6000.md.diff?cvsroot=gcc&r1=1.407&r2=1.408



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774

[Bug target/23774] dealloc of dynamic stack space breaks backchain

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-09-13 03:01 -------
Subject: Bug 23774

CVSROOT:	/cvs/gcc
Module name:	gcc
Branch: 	gcc-4_0-branch
Changes by:	amodra@gcc.gnu.org	2005-09-13 03:01:08

Modified files:
	gcc            : ChangeLog 
	gcc/config/rs6000: rs6000.md 

Log message:
	PR target/23774
	* config/rs6000/rs6000.md (restore_stack_block): Write the backchain
	word before changing the stack pointer.	 Use gen_frame_mem for MEMs.
	Use UNSPEC_TIE to prevent insn scheduling reordering the insns.
	(restore_stack_nonlocal): Likewise.
	(save_stack_nonlocal): Use template to emit insns, and gen_frame_mem.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=2.7592.2.427&r2=2.7592.2.428
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/config/rs6000/rs6000.md.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.350.2.3&r2=1.350.2.4



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774

[Bug target/23774] dealloc of dynamic stack space breaks backchain

[amodra at bigpond dot net dot au]

------- Additional Comments From amodra at bigpond dot net dot au  2005-09-13 04:07 -------
Part (a) Fixed 4.0 and 4.1.  Opening another bug for (c), and (b) isn't worth
worrying about.

4.1 patch relies on http://gcc.gnu.org/ml/gcc-cvs/2005-09/msg00429.html and
http://gcc.gnu.org/ml/gcc-cvs/2005-09/msg00447.html
4.0 on http://gcc.gnu.org/ml/gcc-cvs/2005-09/msg00448.html

Followup fix for 4.0, http://gcc.gnu.org/ml/gcc-cvs/2005-09/msg00480.html


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23774