[Bug c/26549] New: pointer truncation in arch/powerpc/kernel/prom_init.c

[Bug c/26549] New: pointer truncation in arch/powerpc/kernel/prom_init.c

[olh at suse dot de]

The address of variable val in prom_init_stdout is passed to prom_getprop.
prom_getprop casts the pointer to u32 and passes it to call_prom in the hope
that OpenFirmware stores something there.
But the pointer is truncated in the lower bits and the expected value is
stored somewhere else.
This gcc bug does not exist in SLES9 gcc33 toolchain, but it is present in
gcc4.0+, likely also in gcc3.4. Compiling a testcase without any -O produces
also correct code.

In my testing I had a stackpointer of 0x0023e6b4. val was at offset 120, 
wich has address 0x0023e72c. But the value passed to OF was 0x0023e728.

c00000000040b710:       3b 01 00 78     addi    r24,r1,120
...
c00000000040b754:       57 08 00 38     rlwinm  r8,r24,0,0,28
...
c00000000040b784:       80 01 00 78     lwz     r0,120(r1)
...
c00000000040b798:       90 1b 00 0c     stw     r0,12(r27)
...

simple testcase:

int f(unsigned);
void g(void)
{
        unsigned a;
        unsigned int b = (unsigned long)(void*)(&a);
        f(b);
}

asm should look like this:
   c:   38 61 00 70     addi    r3,r1,112
  10:   78 63 00 20     clrldi  r3,r3,32
  14:   48 00 00 01     bl      14 <.g+0x14>

But instead it looks like:
   c:   38 61 00 70     addi    r3,r1,112
  10:   54 63 00 36     rlwinm  r3,r3,0,0,27
  14:   48 00 00 01     bl      14 <.g+0x14>


So just uninline prom_getprop to workaround this gcc bug.

c000000000409034 <.prom_getprop>:
c000000000409054:       7c bc 2b 78     mr      r28,r5
c000000000409074:       7b 88 00 20     clrldi  r8,r28,32
...
c00000000040b29c <.prom_init>:
c00000000040b47c:       e8 82 a1 d8     ld      r4,-24104(r2)
c00000000040b480:       80 61 00 74     lwz     r3,116(r1)
c00000000040b484:       7f 85 e3 78     mr      r5,r28
c00000000040b488:       38 c0 00 10     li      r6,16
c00000000040b48c:       4b c1 c2 95     bl      c000000000027720
<.prom_getprop>
...
c00000000040b4b4:       80 61 00 74     lwz     r3,116(r1)


Signed-off-by: Olaf Hering <olh@suse.de>

 arch/powerpc/kernel/prom_init.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6.16-rc5-olh/arch/powerpc/kernel/prom_init.c
===================================================================
--- linux-2.6.16-rc5-olh.orig/arch/powerpc/kernel/prom_init.c
+++ linux-2.6.16-rc5-olh/arch/powerpc/kernel/prom_init.c
@@ -421,8 +421,8 @@ static int __init prom_next_node(phandle
                        return 1;
        }
 }
-
-static int inline prom_getprop(phandle node, const char *pname,
+/* do not mark as inline to work around gcc bug */
+static int __init prom_getprop(phandle node, const char *pname,
                               void *value, size_t valuelen)
 {
        return call_prom("getprop", 4, 1, node, ADDR(pname),


-- 
           Summary: pointer truncation in arch/powerpc/kernel/prom_init.c
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: olh at suse dot de
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26549

[Bug rtl-optimization/26549] pointer truncation in arch/powerpc/kernel/prom_init.c

[segher at kernel dot crashing dot org]

------- Comment #1 from segher at kernel dot crashing dot org  2006-03-03 16:58 -------
Confirmed, bug is in combine...  looking into it...


-- 

segher at kernel dot crashing dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |segher at kernel dot
                   |                            |crashing dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26549

[Bug rtl-optimization/26549] [3.4/4.0/4.1/4.2 Regression] pointer truncation in arch/powerpc/kernel/prom_init.c

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-03-03 17:29 -------
Confirmed, a regression from at least 3.2.3, I don't have a 3.3.x to test with.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
      Known to work|                            |3.2.3
   Last reconfirmed|0000-00-00 00:00:00         |2006-03-03 17:29:56
               date|                            |
            Summary|pointer truncation in       |[3.4/4.0/4.1/4.2 Regression]
                   |arch/powerpc/kernel/prom_ini|pointer truncation in
                   |t.c                         |arch/powerpc/kernel/prom_ini
                   |                            |t.c
   Target Milestone|---                         |4.0.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26549

[Bug rtl-optimization/26549] [3.4/4.0/4.1/4.2 Regression] pointer truncation in arch/powerpc/kernel/prom_init.c

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2006-03-03 17:30 -------
This is also independent of GNU/Linux as it happens on powerpc-darwin too.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  GCC build triplet|powerpc64-linux             |
   GCC host triplet|powerpc64-linux             |
 GCC target triplet|powerpc64-linux             |powerpc64-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26549

[Bug rtl-optimization/26549] [3.4/4.0/4.1/4.2 Regression] pointer truncation in arch/powerpc/kernel/prom_init.c

[segher at kernel dot crashing dot org]

------- Comment #4 from segher at kernel dot crashing dot org  2006-03-03 18:34 -------
Not a bug at all, actually.  GCC thinks it can mask out the lower few bits,
because GPR1 should
always be 16-byte aligned.  And it isn't in your prom_init testing, and that's
the bug.  Better
figure out how _that_ happened :-)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26549

[Bug rtl-optimization/26549] [3.4/4.0/4.1/4.2 Regression] pointer truncation in arch/powerpc/kernel/prom_init.c

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2006-03-03 18:51 -------
Problem else where, and not in this piece of source.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WORKSFORME


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26549