On Mon, 13 Jun 2005, Andy Dougherty wrote:
> On Mon, 13 Jun 2005, Leopold Toetsch via RT wrote:
>
> > Chip Salzenberg wrote:
> > > On Mon, Jun 13, 2005 at 02:57:09PM -0400, Andy Dougherty wrote:
> >
> > >>Yes. The compiler does the right thing. It sensibly reports
> > >>that sizeof(PMC) = 24 for SPARC.
> > >
> > > Then I remain puzzled how Parrot could ever misalign a double.
> >
> > Yes. So I am. Could somone please run this PASM snippet in a debugger so
> > that we can see, where it fails.
>
> Here's where it fails:
>
> (dbx) run ../num2.pasm
> (process id 7721)
> [EMAIL PROTECTED] ([EMAIL PROTECTED]) signal BUS (invalid address alignment)
> in Parrot_set_n_nc (optimized) at line 149 in file "set.ops"
> 149 goto NEXT();
> (dbx) where
> current thread: [EMAIL PROTECTED]
> =>[1] Parrot_set_n_nc(cur_opcode = ???, interpreter = ???) (optimized), at
> 0xa9160 (line ~149) in "set.ops"
> [2] runops_slow_core(interpreter = ???, pc = ???) (optimized), at 0xdd2a0
> (line ~105) in "runops_cores.c"
> [3] runops_int(interpreter = ???, offset = ???) (optimized), at 0xdbc70 (line
> ~657) in "interpreter.c"
> [4] runops(interpreter = ???, offs = ???) (optimized), at 0xdc6d4 (line ~40)
> in "inter_run.c"
> [5] Parrot_runcode(interpreter = ???, argc = ???, argv = ???) (optimized), at
> 0x8482c (line ~757) in "embed.c"
> [6] Parrot_runcode(interpreter = ???, argc = ???, argv = ???) (optimized), at
> 0x846ac (line ~757) in "embed.c"
> [7] main(argc = ???, argv = ???) (optimized), at 0x68058 (line ~448) in
> "main.c"
>
> Alas, since this is an optimized compile, there is no single stepping in the
> debugger.
The following patch fixes the core dump for me. The problem appears to be
in <stacks.h>, where the 'data' segment is declared as a (void *), but is
then assumed to be aligned suitably for holding a double. I fixed that
with a union. The compiler then automatically assures that the elements
are aligned. I still need to go through places where the data element is
assigned to various things through casts and check whether any additional
members to the union ought to be added.
While hunting for a solution, I saw a lot of places in the code that
appear to be worried about alignment. In many cases it was not clear to
me what needs to be aligned with what and why. Is it for alignment of
doubles? Then we should use a double type where appropriate. Is it for
alignment of one structure with another (like perl's sv/av/hv/
structures)? If so, that should be documented carefully somewhere. Is it
for alignment with blocks returned by memalign? I didn't know, so I put
in questions in the comments.
Gcc currently gives the warning:
cast increases required alignment of target type 7,151 times. One of
those was actually the key to solving this problem. Eventually, it'd be
nice to get rid of the other 7150, even if they are all false alarms.
diff -r -u parrot-orig/include/parrot/debug.h parrot-andy/include/parrot/debug.h
--- parrot-orig/include/parrot/debug.h Mon Jun 6 09:07:45 2005
+++ parrot-andy/include/parrot/debug.h Tue Jun 14 14:01:06 2005
@@ -52,8 +52,8 @@
typedef struct PDB_condition {
unsigned short type;
unsigned char reg;
- unsigned char dummy; /* For alignment */
- void *value;
+ unsigned char dummy; /* For alignment XXX ?? */
+ void *value; /* What neeeds to be aligned with
what? */
PDB_condition_ptr next;
} PDB_condition_t;
diff -r -u parrot-orig/include/parrot/jit.h parrot-andy/include/parrot/jit.h
--- parrot-orig/include/parrot/jit.h Mon Jun 6 09:08:05 2005
+++ parrot-andy/include/parrot/jit.h Tue Jun 14 14:02:54 2005
@@ -30,8 +30,8 @@
int type;
ptrdiff_t native_offset;
char skip;
- char dummy[3]; /* For alignment */
- union {
+ char dummy[3]; /* For alignment ??? XXX */
+ union { /* What has to align with what? */
opcode_t opcode;
void (*fptr)(void);
} param;
@@ -124,8 +124,8 @@
char isjit;
char done;
char ins_count;
- char dummy; /* For alignment */
- int block;
+ char dummy; /* For alignment ??? XXX */
+ int block; /* What has to align with
what? */
Parrot_jit_optimizer_section_ptr branch_target;
Parrot_jit_optimizer_section_ptr prev;
Parrot_jit_optimizer_section_ptr next;
@@ -151,8 +151,8 @@
char *map_branch;
opcode_t **branch_list;
unsigned char has_unpredictable_jump;
- unsigned char dummy[3]; /* For alignment */
-} Parrot_jit_optimizer_t;
+ unsigned char dummy[3]; /* For alignment ??? XXX */
+} Parrot_jit_optimizer_t; /* What has to align with what?
*/
/* Parrot_jit_constant_pool_t
* Constants pool information.
diff -r -u parrot-orig/include/parrot/smallobject.h
parrot-andy/include/parrot/smallobject.h
--- parrot-orig/include/parrot/smallobject.h Mon Jun 6 09:07:38 2005
+++ parrot-andy/include/parrot/smallobject.h Tue Jun 14 14:04:34 2005
@@ -52,6 +52,7 @@
*
* XXX this could lead to unaligned FLOATVALs in the adjacent PMC
* if that's true either insert a dummy or reorder PMC members
+ * ??? How is that possible?
*/
typedef struct _gc_gms_hdr {
struct _gc_gms_hdr *prev;
diff -r -u parrot-orig/include/parrot/stacks.h
parrot-andy/include/parrot/stacks.h
--- parrot-orig/include/parrot/stacks.h Mon Jun 6 09:08:06 2005
+++ parrot-andy/include/parrot/stacks.h Tue Jun 14 14:00:11 2005
@@ -28,13 +28,13 @@
int size;
const char * name;
struct Stack_Chunk *prev;
-#if ! DISABLE_GC_DEBUG
- void * dummy; /* force 8 byte align */
-#endif
- void *data;
+ union { /* force appropriate alignment of 'data' */
+ void *data;
+ double d_dummy;
+ } u;
} Stack_Chunk_t;
-#define STACK_DATAP(chunk) &chunk->data
+#define STACK_DATAP(chunk) &chunk->u.data
/* #define STACK_ITEMSIZE(chunk) PObj_buflen(chunk) */
diff -r -u parrot-orig/src/stack_common.c parrot-andy/src/stack_common.c
--- parrot-orig/src/stack_common.c Mon Jun 6 09:02:00 2005
+++ parrot-andy/src/stack_common.c Tue Jun 14 13:15:13 2005
@@ -58,7 +58,7 @@
{
Stack_Chunk_t *chunk;
- item_size += offsetof(Stack_Chunk_t, data);
+ item_size += offsetof(Stack_Chunk_t, u.data);
item_size += 7;
item_size &= ~7; /* round up to 8 so that the chunk is aligned at
the same size - the aligned MMX memcpy needs it */
--
Andy Dougherty [EMAIL PROTECTED]
