[03/10] tree-object-size: Use tree instead of HOST_WIDE_INT

  Transform tree-object-size to operate on tree objects instead of host
wide integers.  This makes it easier to extend to dynamic expressions
for object sizes.

The compute_builtin_object_size interface also now returns a tree
expression instead of HOST_WIDE_INT, so callers have been adjusted to
account for that.

gcc/ChangeLog:

	* tree-object-size.h (compute_builtin_object_size): Return tree
	instead of HOST_WIDE_INT.
	* builtins.c (fold_builtin_object_size): Adjust.
	* gimple-fold.c (gimple_fold_builtin_strncat): Likewise.
	* ubsan.c (instrument_object_size): Likewise.
	* tree-object-size.c (object_sizes): Change type to vec<tree>.
	(initval): New function.
	(unknown): Use it.
	(size_unknown_p, size_initval, size_unknown): New functions.
	(object_sizes_unknown_p): Use it.
	(object_sizes_get): Return tree.
	(object_sizes_initialize): Rename from object_sizes_set_force
	and set VAL parameter type as tree.
	(object_sizes_set): Set VAL parameter type as tree and adjust
	implementation.
	(size_for_offset): New function.
	(addr_object_size): Change PSIZE parameter to tree and adjust
	implementation.
	(alloc_object_size): Return tree.
	(compute_builtin_object_size): Return tree in PSIZE.
	(expr_object_size, call_object_size, unknown_object_size):
	Adjust for object_sizes_set change.
	(merge_object_sizes): Set OFFSET type to tree and adjust
	implementation.
	(plus_stmt_object_size, cond_expr_object_size,
	collect_object_sizes_for, check_for_plus_in_loops_1): Adjust for
	change of type from HOST_WIDE_INT to tree.
	(object_sizes_execute): Adjust for type change to tree.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>
---
 gcc/builtins.c         |  10 +-
 gcc/gimple-fold.c      |   9 +-
 gcc/tree-object-size.c | 253 ++++++++++++++++++++++-------------------
 gcc/tree-object-size.h |   2 +-
 gcc/ubsan.c            |  46 ++++----
 5 files changed, 168 insertions(+), 152 deletions(-)
  

On Wed, Nov 10, 2021 at 12:31:29AM +0530, Siddhesh Poyarekar wrote:
> 	* tree-object-size.h (compute_builtin_object_size): Return tree
> 	instead of HOST_WIDE_INT.
> 	* builtins.c (fold_builtin_object_size): Adjust.
> 	* gimple-fold.c (gimple_fold_builtin_strncat): Likewise.
> 	* ubsan.c (instrument_object_size): Likewise.
> 	* tree-object-size.c (object_sizes): Change type to vec<tree>.
> 	(initval): New function.
> 	(unknown): Use it.
> 	(size_unknown_p, size_initval, size_unknown): New functions.
> 	(object_sizes_unknown_p): Use it.
> 	(object_sizes_get): Return tree.
> 	(object_sizes_initialize): Rename from object_sizes_set_force
> 	and set VAL parameter type as tree.
> 	(object_sizes_set): Set VAL parameter type as tree and adjust
> 	implementation.
> 	(size_for_offset): New function.
> 	(addr_object_size): Change PSIZE parameter to tree and adjust
> 	implementation.
> 	(alloc_object_size): Return tree.
> 	(compute_builtin_object_size): Return tree in PSIZE.
> 	(expr_object_size, call_object_size, unknown_object_size):
> 	Adjust for object_sizes_set change.
> 	(merge_object_sizes): Set OFFSET type to tree and adjust
> 	implementation.
> 	(plus_stmt_object_size, cond_expr_object_size,
> 	collect_object_sizes_for, check_for_plus_in_loops_1): Adjust for
> 	change of type from HOST_WIDE_INT to tree.
> 	(object_sizes_execute): Adjust for type change to tree.

> --- a/gcc/builtins.c
> +++ b/gcc/builtins.c
> @@ -10226,7 +10226,7 @@ maybe_emit_sprintf_chk_warning (tree exp, enum built_in_function fcode)
>  static tree
>  fold_builtin_object_size (tree ptr, tree ost)
>  {
> -  unsigned HOST_WIDE_INT bytes;
> +  tree bytes;
>    int object_size_type;
>  
>    if (!validate_arg (ptr, POINTER_TYPE)
> @@ -10251,17 +10251,15 @@ fold_builtin_object_size (tree ptr, tree ost)
>    if (TREE_CODE (ptr) == ADDR_EXPR)
>      {
>        compute_builtin_object_size (ptr, object_size_type, &bytes);
> -      if (wi::fits_to_tree_p (bytes, size_type_node))
> -	return build_int_cstu (size_type_node, bytes);
> +      return fold_convert (size_type_node, bytes);
>      }
>    else if (TREE_CODE (ptr) == SSA_NAME)
>      {
>        /* If object size is not known yet, delay folding until
>         later.  Maybe subsequent passes will help determining
>         it.  */
> -      if (compute_builtin_object_size (ptr, object_size_type, &bytes)
> -	  && wi::fits_to_tree_p (bytes, size_type_node))
> -	return build_int_cstu (size_type_node, bytes);
> +      if (compute_builtin_object_size (ptr, object_size_type, &bytes))
> +	return fold_convert (size_type_node, bytes);

Neither of these are equivalent to what it used to do before.
If some target has e.g. pointers wider than size_t, then previously we could
compute bytes that doesn't fit into size_t and would return NULL which
eventually would result in object_sizes_execute or expand_builtin_object_size
resolving it to the unknown value.  But fold_convert will perform modulo
arithmetics on it, so say if size_t is 24-bit and bytes is 0x1000001, it
will fold to (size_t) 1.  I think we should still punt if it doesn't fit.
Or do we ensure that what it returns always has sizetype type?

> @@ -2486,13 +2486,14 @@ gimple_fold_builtin_strncat (gimple_stmt_iterator *gsi)
>    if (cmpsrc < 0)
>      return false;
>  
> -  unsigned HOST_WIDE_INT dstsize;
> +  tree dstsize;
>  
>    bool nowarn = warning_suppressed_p (stmt, OPT_Wstringop_overflow_);
>  
> -  if (!nowarn && compute_builtin_object_size (dst, 1, &dstsize))
> +  if (!nowarn && compute_builtin_object_size (dst, 1, &dstsize)
> +      && tree_fits_uhwi_p (dstsize))
>      {
> -      int cmpdst = compare_tree_int (len, dstsize);
> +      int cmpdst = compare_tree_int (len, tree_to_uhwi (dstsize));

Why jump from tree to UHWI and back?
Check that TREE_CODE (dstsize) == INTEGER_CST and do
tree_int_cst_compare instead?

>  
>        if (cmpdst >= 0)
>  	{
> @@ -2509,7 +2510,7 @@ gimple_fold_builtin_strncat (gimple_stmt_iterator *gsi)
>  				    "destination size")
>  			       : G_("%qD specified bound %E exceeds "
>  				    "destination size %wu"),
> -			       fndecl, len, dstsize);
> +			       fndecl, len, tree_to_uhwi (dstsize));

Similarly, use %E and pass dstsize to it.

> +/* Initial value of object sizes; zero for maximum and SIZE_MAX for minimum
> +   object size.  */
> +
> +static inline unsigned HOST_WIDE_INT
> +initval (int object_size_type)
> +{
> +  return (unsigned HOST_WIDE_INT) -popcount_hwi (object_size_type
> +						 & OST_MINIMUM);

This makes the code quite unreadable and on some arches it will be also
much worse (popcount is a libcall on many, and even if not, it is inline
function using a builtin inside of it).  Can't you use a simple readable
  return (object_size_type & OST_MINUMUM) ? HOST_WIDE_INT_M1U : 0;
and let the compiler optimize as much as it wants?
?

> +/* Bytes at end of the object with SZ from offset OFFSET. */
> +
> +static tree
> +size_for_offset (tree sz, tree offset)
> +{
> +  return size_binop (MINUS_EXPR, size_binop (MAX_EXPR, sz, offset), offset);
> +}
>  
> @@ -314,27 +356,22 @@ addr_object_size (struct object_size_info *osi, const_tree ptr,
>  			    SSA_NAME_VERSION (var)))
>  	    sz = object_sizes_get (osi, SSA_NAME_VERSION (var));
>  	  else
> -	    sz = unknown (object_size_type);
> +	    sz = size_unknown (object_size_type);
>  	}
> -      if (sz != unknown (object_size_type))
> +      if (!size_unknown_p (sz, object_size_type))
>  	{
> -	  offset_int mem_offset;
> -	  if (mem_ref_offset (pt_var).is_constant (&mem_offset))
> -	    {
> -	      offset_int dsz = wi::sub (sz, mem_offset);
> -	      if (wi::neg_p (dsz))
> -		sz = 0;
> -	      else if (wi::fits_uhwi_p (dsz))
> -		sz = dsz.to_uhwi ();
> -	      else
> -		sz = unknown (object_size_type);
> -	    }
> +	  tree offset = TREE_OPERAND (pt_var, 1);
> +	  if (TREE_CODE (offset) != INTEGER_CST
> +	      || TREE_CODE (sz) != INTEGER_CST)
> +	    sz = size_unknown (object_size_type);
>  	  else
> -	    sz = unknown (object_size_type);
> +	    sz = size_for_offset (sz, offset);

This doesn't match what the code did and I'm surprised if it works at all.
TREE_OPERAND (pt_var, 1), while it is an INTEGER_CST or POLY_INT_CST,
has in its type encoded the type for aliasing, so the type is some pointer
type.  Performing size_binop etc. on such values can misbehave, the code
assumes that it is sizetype or at least some integral type compatible with
it.Also, mem_ref_offset is signed and offset_int has bigger precision
than pointers on the target such that it can be always signed.  So
e.g. if MEM_REF's second operand is bigger or equal than half of the
address space, in the old code it would appear to be negative, wi::sub would
result in a value bigger than sz.  Not really sure right now if that is
exactly how we want to treat it, would be nice to try some testcase.
In any case, size_for_offset should be called with the offset converted
to sizetype if it does size_binop on it.
> +    reexamine |= merge_object_sizes (osi, var, then_, size_int (0));

size_zero_node ?
>    else
>      expr_object_size (osi, var, then_);
>  
> @@ -952,7 +970,7 @@ cond_expr_object_size (struct object_size_info *osi, tree var, gimple *stmt)
>      return reexamine;
>  
>    if (TREE_CODE (else_) == SSA_NAME)
> -    reexamine |= merge_object_sizes (osi, var, else_, 0);
> +    reexamine |= merge_object_sizes (osi, var, else_, size_int (0));

Likewise.  Many times.

> -  unsigned HOST_WIDE_INT size;
> -  if (compute_builtin_object_size (base_addr, 0, &size))
> -    sizet = build_int_cst (sizetype, size);
> -  else if (optimize)

I'd prefer not to reindent it to avoid useless churn, just do
  if (compute_builtin_object_size (base_addr, 0, &sizet))
    ;
  else if (optimize)
...

	Jakub
  

On 11/19/21 22:36, Jakub Jelinek wrote:
> On Wed, Nov 10, 2021 at 12:31:29AM +0530, Siddhesh Poyarekar wrote:
>> 	* tree-object-size.h (compute_builtin_object_size): Return tree
>> 	instead of HOST_WIDE_INT.
>> 	* builtins.c (fold_builtin_object_size): Adjust.
>> 	* gimple-fold.c (gimple_fold_builtin_strncat): Likewise.
>> 	* ubsan.c (instrument_object_size): Likewise.
>> 	* tree-object-size.c (object_sizes): Change type to vec<tree>.
>> 	(initval): New function.
>> 	(unknown): Use it.
>> 	(size_unknown_p, size_initval, size_unknown): New functions.
>> 	(object_sizes_unknown_p): Use it.
>> 	(object_sizes_get): Return tree.
>> 	(object_sizes_initialize): Rename from object_sizes_set_force
>> 	and set VAL parameter type as tree.
>> 	(object_sizes_set): Set VAL parameter type as tree and adjust
>> 	implementation.
>> 	(size_for_offset): New function.
>> 	(addr_object_size): Change PSIZE parameter to tree and adjust
>> 	implementation.
>> 	(alloc_object_size): Return tree.
>> 	(compute_builtin_object_size): Return tree in PSIZE.
>> 	(expr_object_size, call_object_size, unknown_object_size):
>> 	Adjust for object_sizes_set change.
>> 	(merge_object_sizes): Set OFFSET type to tree and adjust
>> 	implementation.
>> 	(plus_stmt_object_size, cond_expr_object_size,
>> 	collect_object_sizes_for, check_for_plus_in_loops_1): Adjust for
>> 	change of type from HOST_WIDE_INT to tree.
>> 	(object_sizes_execute): Adjust for type change to tree.
> 
>> --- a/gcc/builtins.c
>> +++ b/gcc/builtins.c
>> @@ -10226,7 +10226,7 @@ maybe_emit_sprintf_chk_warning (tree exp, enum built_in_function fcode)
>>   static tree
>>   fold_builtin_object_size (tree ptr, tree ost)
>>   {
>> -  unsigned HOST_WIDE_INT bytes;
>> +  tree bytes;
>>     int object_size_type;
>>   
>>     if (!validate_arg (ptr, POINTER_TYPE)
>> @@ -10251,17 +10251,15 @@ fold_builtin_object_size (tree ptr, tree ost)
>>     if (TREE_CODE (ptr) == ADDR_EXPR)
>>       {
>>         compute_builtin_object_size (ptr, object_size_type, &bytes);
>> -      if (wi::fits_to_tree_p (bytes, size_type_node))
>> -	return build_int_cstu (size_type_node, bytes);
>> +      return fold_convert (size_type_node, bytes);
>>       }
>>     else if (TREE_CODE (ptr) == SSA_NAME)
>>       {
>>         /* If object size is not known yet, delay folding until
>>          later.  Maybe subsequent passes will help determining
>>          it.  */
>> -      if (compute_builtin_object_size (ptr, object_size_type, &bytes)
>> -	  && wi::fits_to_tree_p (bytes, size_type_node))
>> -	return build_int_cstu (size_type_node, bytes);
>> +      if (compute_builtin_object_size (ptr, object_size_type, &bytes))
>> +	return fold_convert (size_type_node, bytes);
> 
> Neither of these are equivalent to what it used to do before.
> If some target has e.g. pointers wider than size_t, then previously we could
> compute bytes that doesn't fit into size_t and would return NULL which
> eventually would result in object_sizes_execute or expand_builtin_object_size
> resolving it to the unknown value.  But fold_convert will perform modulo
> arithmetics on it, so say if size_t is 24-bit and bytes is 0x1000001, it
> will fold to (size_t) 1.  I think we should still punt if it doesn't fit.
> Or do we ensure that what it returns always has sizetype type?

compute_builtin_object_size should always return sizetype.  I probably 
haven't strictly ensured that but I could do that.  Would it be 
necessary to check for fit in sizetype -> size_type_node conversion too? 
  I've been assuming that they'd have the same precision.

> 
>> @@ -2486,13 +2486,14 @@ gimple_fold_builtin_strncat (gimple_stmt_iterator *gsi)
>>     if (cmpsrc < 0)
>>       return false;
>>   
>> -  unsigned HOST_WIDE_INT dstsize;
>> +  tree dstsize;
>>   
>>     bool nowarn = warning_suppressed_p (stmt, OPT_Wstringop_overflow_);
>>   
>> -  if (!nowarn && compute_builtin_object_size (dst, 1, &dstsize))
>> +  if (!nowarn && compute_builtin_object_size (dst, 1, &dstsize)
>> +      && tree_fits_uhwi_p (dstsize))
>>       {
>> -      int cmpdst = compare_tree_int (len, dstsize);
>> +      int cmpdst = compare_tree_int (len, tree_to_uhwi (dstsize));
> 
> Why jump from tree to UHWI and back?
> Check that TREE_CODE (dstsize) == INTEGER_CST and do
> tree_int_cst_compare instead?
> 
>>   
>>         if (cmpdst >= 0)
>>   	{
>> @@ -2509,7 +2510,7 @@ gimple_fold_builtin_strncat (gimple_stmt_iterator *gsi)
>>   				    "destination size")
>>   			       : G_("%qD specified bound %E exceeds "
>>   				    "destination size %wu"),
>> -			       fndecl, len, dstsize);
>> +			       fndecl, len, tree_to_uhwi (dstsize));
> 
> Similarly, use %E and pass dstsize to it.
> 

I noticed it while doing the gimple fold patches; I'll fix it.  I need 
to rebase this bit anyway.

>> +/* Initial value of object sizes; zero for maximum and SIZE_MAX for minimum
>> +   object size.  */
>> +
>> +static inline unsigned HOST_WIDE_INT
>> +initval (int object_size_type)
>> +{
>> +  return (unsigned HOST_WIDE_INT) -popcount_hwi (object_size_type
>> +						 & OST_MINIMUM);
> 
> This makes the code quite unreadable and on some arches it will be also
> much worse (popcount is a libcall on many, and even if not, it is inline
> function using a builtin inside of it).  Can't you use a simple readable
>    return (object_size_type & OST_MINUMUM) ? HOST_WIDE_INT_M1U : 0;
> and let the compiler optimize as much as it wants?
> ?

OK, I'll do that; I was trying too hard there I suppose :)

> 
>> +/* Bytes at end of the object with SZ from offset OFFSET. */
>> +
>> +static tree
>> +size_for_offset (tree sz, tree offset)
>> +{
>> +  return size_binop (MINUS_EXPR, size_binop (MAX_EXPR, sz, offset), offset);
>> +}
>>   
>> @@ -314,27 +356,22 @@ addr_object_size (struct object_size_info *osi, const_tree ptr,
>>   			    SSA_NAME_VERSION (var)))
>>   	    sz = object_sizes_get (osi, SSA_NAME_VERSION (var));
>>   	  else
>> -	    sz = unknown (object_size_type);
>> +	    sz = size_unknown (object_size_type);
>>   	}
>> -      if (sz != unknown (object_size_type))
>> +      if (!size_unknown_p (sz, object_size_type))
>>   	{
>> -	  offset_int mem_offset;
>> -	  if (mem_ref_offset (pt_var).is_constant (&mem_offset))
>> -	    {
>> -	      offset_int dsz = wi::sub (sz, mem_offset);
>> -	      if (wi::neg_p (dsz))
>> -		sz = 0;
>> -	      else if (wi::fits_uhwi_p (dsz))
>> -		sz = dsz.to_uhwi ();
>> -	      else
>> -		sz = unknown (object_size_type);
>> -	    }
>> +	  tree offset = TREE_OPERAND (pt_var, 1);
>> +	  if (TREE_CODE (offset) != INTEGER_CST
>> +	      || TREE_CODE (sz) != INTEGER_CST)
>> +	    sz = size_unknown (object_size_type);
>>   	  else
>> -	    sz = unknown (object_size_type);
>> +	    sz = size_for_offset (sz, offset);
> 
> This doesn't match what the code did and I'm surprised if it works at all.
> TREE_OPERAND (pt_var, 1), while it is an INTEGER_CST or POLY_INT_CST,
> has in its type encoded the type for aliasing, so the type is some pointer
> type.  Performing size_binop etc. on such values can misbehave, the code
> assumes that it is sizetype or at least some integral type compatible with
> it.Also, mem_ref_offset is signed and offset_int has bigger precision
> than pointers on the target such that it can be always signed.  So
> e.g. if MEM_REF's second operand is bigger or equal than half of the
> address space, in the old code it would appear to be negative, wi::sub would
> result in a value bigger than sz.  Not really sure right now if that is
> exactly how we want to treat it, would be nice to try some testcase.

Let me try coming up with a test case for it.

> In any case, size_for_offset should be called with the offset converted
> to sizetype if it does size_binop on it.

I'll fix this.

>> +    reexamine |= merge_object_sizes (osi, var, then_, size_int (0));
> 
> size_zero_node ?
>>     else
>>       expr_object_size (osi, var, then_);
>>   
>> @@ -952,7 +970,7 @@ cond_expr_object_size (struct object_size_info *osi, tree var, gimple *stmt)
>>       return reexamine;
>>   
>>     if (TREE_CODE (else_) == SSA_NAME)
>> -    reexamine |= merge_object_sizes (osi, var, else_, 0);
>> +    reexamine |= merge_object_sizes (osi, var, else_, size_int (0));
> 
> Likewise.  Many times.

OK.

>> -  unsigned HOST_WIDE_INT size;
>> -  if (compute_builtin_object_size (base_addr, 0, &size))
>> -    sizet = build_int_cst (sizetype, size);
>> -  else if (optimize)
> 
> I'd prefer not to reindent it to avoid useless churn, just do
>    if (compute_builtin_object_size (base_addr, 0, &sizet))
>      ;
>    else if (optimize)

OK.

> ...
> 
> 	Jakub
> 

Thanks,
Siddhesh
  

On Sat, Nov 20, 2021 at 12:31:19AM +0530, Siddhesh Poyarekar wrote:
> > Neither of these are equivalent to what it used to do before.
> > If some target has e.g. pointers wider than size_t, then previously we could
> > compute bytes that doesn't fit into size_t and would return NULL which
> > eventually would result in object_sizes_execute or expand_builtin_object_size
> > resolving it to the unknown value.  But fold_convert will perform modulo
> > arithmetics on it, so say if size_t is 24-bit and bytes is 0x1000001, it
> > will fold to (size_t) 1.  I think we should still punt if it doesn't fit.
> > Or do we ensure that what it returns always has sizetype type?
> 
> compute_builtin_object_size should always return sizetype.  I probably
> haven't strictly ensured that but I could do that.  Would it be necessary to
> check for fit in sizetype -> size_type_node conversion too?  I've been
> assuming that they'd have the same precision.

sizetype and size_type_node should be indeed always the same precision.

	Jakub
  

On Fri, Nov 19, 2021 at 8:17 PM Jakub Jelinek via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Sat, Nov 20, 2021 at 12:31:19AM +0530, Siddhesh Poyarekar wrote:
> > > Neither of these are equivalent to what it used to do before.
> > > If some target has e.g. pointers wider than size_t, then previously we could
> > > compute bytes that doesn't fit into size_t and would return NULL which
> > > eventually would result in object_sizes_execute or expand_builtin_object_size
> > > resolving it to the unknown value.  But fold_convert will perform modulo
> > > arithmetics on it, so say if size_t is 24-bit and bytes is 0x1000001, it
> > > will fold to (size_t) 1.  I think we should still punt if it doesn't fit.
> > > Or do we ensure that what it returns always has sizetype type?
> >
> > compute_builtin_object_size should always return sizetype.  I probably
> > haven't strictly ensured that but I could do that.  Would it be necessary to
> > check for fit in sizetype -> size_type_node conversion too?  I've been
> > assuming that they'd have the same precision.
>
> sizetype and size_type_node should be indeed always the same precision.

I don't think so.  vms.h has

/* Always a 32 bit type.  */
#undef SIZE_TYPE
#define SIZE_TYPE  "unsigned int"

...

#define SIZETYPE (flag_vms_pointer_size == VMS_POINTER_SIZE_NONE ? \
                  "unsigned int" : "long long unsigned int")

interestingly that's the _only_ SIZETYPE override we have, so it does look like
we might want to try removing the 'SIZETYPE' target macro.  I'm not sure the
above does anything good - it looks more like a ptr_mode vs Pmode thing.

Richard.

>         Jakub
>
  

On 11/20/21 00:31, Siddhesh Poyarekar wrote:
>> This doesn't match what the code did and I'm surprised if it works at 
>> all.
>> TREE_OPERAND (pt_var, 1), while it is an INTEGER_CST or POLY_INT_CST,
>> has in its type encoded the type for aliasing, so the type is some 
>> pointer
>> type.  Performing size_binop etc. on such values can misbehave, the code
>> assumes that it is sizetype or at least some integral type compatible 
>> with
>> it.Also, mem_ref_offset is signed and offset_int has bigger precision
>> than pointers on the target such that it can be always signed.  So
>> e.g. if MEM_REF's second operand is bigger or equal than half of the
>> address space, in the old code it would appear to be negative, wi::sub 
>> would
>> result in a value bigger than sz.  Not really sure right now if that is
>> exactly how we want to treat it, would be nice to try some testcase.
> 
> Let me try coming up with a test case for it.
> 

So I played around a bit with this.  Basically:

char buf[8];

__SIZE_TYPE__ test (void)
{
   char *p = &buf[0x90000004];
   return __builtin_object_size (p + 2, 0);
}

when built with -m32 returns 0x70000002 but on 64-bit, returns 0 as 
expected.  of course, with subscript as 0x9000000000000004, 64-bit gives 
  0x7000000000000002 as the result.

With the tree conversion, this is at least partly taken care of since 
offset larger than size, to the extent that it fits into sizetype, 
returns a size of zero.  So in the above example, the size returned is 
zero in both -m32 as well as -m64.  Likewise for negative offset, i.e. 
&buf[-4]; the old code returns 10 while with trees it returns 0, which 
seems correct to me since it is an underflow.

It's only partly taken care of because, e.g.

   char *p = &buf[0x100000004];

ends up truncating the offset, returning object size of 2.  This however 
is an unrelated problem; it's the folding of offsets that is responsible 
for this since it ends up truncating the offset to shwi bounds.  Perhaps 
there's an opportunity in get_addr_base_and_unit_offset to warn of 
overflow if offset goes above pointer precision before truncating it.

So for this patch, may I simply ensure that offset is converted to 
sizetype and keep everything else the same?  it appears to demonstrate 
better behaviour than the older code.  I'll also add these tests.

Thanks,
Siddhesh
  

On Mon, Nov 22, 2021 at 03:41:57PM +0530, Siddhesh Poyarekar wrote:
> So I played around a bit with this.  Basically:
> 
> char buf[8];
> 
> __SIZE_TYPE__ test (void)
> {
>   char *p = &buf[0x90000004];
>   return __builtin_object_size (p + 2, 0);
> }
> 
> when built with -m32 returns 0x70000002 but on 64-bit, returns 0 as
> expected.  of course, with subscript as 0x9000000000000004, 64-bit gives
> 0x7000000000000002 as the result.

That is one case, I think when the base is a ADDR_EXPR VAR_DECL, offsets
larger than half of the address space will be UB, though of course the
question is what __bos should return for that because it wants to prevent
UB exploiting.

Another case is where the base is some pointer, something like
  &MEM_REF [ptr, -16].a
etc., where the MEM_REF offset negative makes a lot of sense,
there could be
  ptr = &var + 32;
earlier etc.
That gives us to the general question on what to do with POINTER_PLUS_EXPR
if the offset is constant but "negative" (as it is sizetype, it is never
negative, but usually we treat it or should treat it as signed in the end).
If the offset is "negative", for e.g. __bos 0/1 one option is to use a
conservative maximum, i.e. subtract the offset from the value (make it even
larger, of course make sure it doesn't wrap around).  Another one would be
to consider also __bos 2 in that case, if the negation of the offset is
bigger than __bos 2, then the pointer points to before the start of the
object and we could return 0.

	Jakub
  

On 11/22/21 16:01, Jakub Jelinek wrote:
> On Mon, Nov 22, 2021 at 03:41:57PM +0530, Siddhesh Poyarekar wrote:
>> So I played around a bit with this.  Basically:
>>
>> char buf[8];
>>
>> __SIZE_TYPE__ test (void)
>> {
>>    char *p = &buf[0x90000004];
>>    return __builtin_object_size (p + 2, 0);
>> }
>>
>> when built with -m32 returns 0x70000002 but on 64-bit, returns 0 as
>> expected.  of course, with subscript as 0x9000000000000004, 64-bit gives
>> 0x7000000000000002 as the result.
> 
> That is one case, I think when the base is a ADDR_EXPR VAR_DECL, offsets
> larger than half of the address space will be UB, though of course the
> question is what __bos should return for that because it wants to prevent
> UB exploiting.
> 
> Another case is where the base is some pointer, something like
>    &MEM_REF [ptr, -16].a
> etc., where the MEM_REF offset negative makes a lot of sense,
> there could be
>    ptr = &var + 32;
> earlier etc.
> That gives us to the general question on what to do with POINTER_PLUS_EXPR
> if the offset is constant but "negative" (as it is sizetype, it is never
> negative, but usually we treat it or should treat it as signed in the end).
> If the offset is "negative", for e.g. __bos 0/1 one option is to use a
> conservative maximum, i.e. subtract the offset from the value (make it even
> larger, of course make sure it doesn't wrap around).  Another one would be
> to consider also __bos 2 in that case, if the negation of the offset is
> bigger than __bos 2, then the pointer points to before the start of the
> object and we could return 0.

So I've got patch 10/10, which handles dynamic (and consequently 
negative) offsets.  It basically computes a "whole size", which then 
gives the extent to which a negative offset is valid, making the 
estimates a bit more precise.  I didn't do it for static object sizes 
because I didn't have time then, but I could add a patch 11/10 if the 
idea sounds OK to you.

Siddhesh
  

On 11/22/21 17:30, Siddhesh Poyarekar wrote:
> So I've got patch 10/10, which handles dynamic (and consequently 
> negative) offsets.  It basically computes a "whole size", which then 
> gives the extent to which a negative offset is valid, making the 
> estimates a bit more precise.  I didn't do it for static object sizes 
> because I didn't have time then, but I could add a patch 11/10 if the 
> idea sounds OK to you.

... or alternatively, I could bring the whole size idea into this tree 
conversion patch so that it handles all kinds of offsets.  That might 
even eliminate patch 10/10.  What would you prefer?

Siddhesh
  

On Mon, Nov 22, 2021 at 06:01:08PM +0530, Siddhesh Poyarekar wrote:
> On 11/22/21 17:30, Siddhesh Poyarekar wrote:
> > So I've got patch 10/10, which handles dynamic (and consequently
> > negative) offsets.  It basically computes a "whole size", which then
> > gives the extent to which a negative offset is valid, making the
> > estimates a bit more precise.  I didn't do it for static object sizes
> > because I didn't have time then, but I could add a patch 11/10 if the
> > idea sounds OK to you.
> 
> ... or alternatively, I could bring the whole size idea into this tree
> conversion patch so that it handles all kinds of offsets.  That might even
> eliminate patch 10/10.  What would you prefer?

Into this patch.

	Jakub
  

On Mon, Nov 22, 2021 at 01:32:22PM +0100, Jakub Jelinek via Gcc-patches wrote:
> On Mon, Nov 22, 2021 at 06:01:08PM +0530, Siddhesh Poyarekar wrote:
> > On 11/22/21 17:30, Siddhesh Poyarekar wrote:
> > > So I've got patch 10/10, which handles dynamic (and consequently
> > > negative) offsets.  It basically computes a "whole size", which then
> > > gives the extent to which a negative offset is valid, making the
> > > estimates a bit more precise.  I didn't do it for static object sizes
> > > because I didn't have time then, but I could add a patch 11/10 if the
> > > idea sounds OK to you.
> > 
> > ... or alternatively, I could bring the whole size idea into this tree
> > conversion patch so that it handles all kinds of offsets.  That might even
> > eliminate patch 10/10.  What would you prefer?
> 
> Into this patch.

BTW, seems the current behavior is to punt on those "negative" values,
we trigger
  if (offset >= offset_limit)
case for it and return unknown.

	Jakub
  

On 11/23/21 17:28, Jakub Jelinek wrote:
> On Mon, Nov 22, 2021 at 01:32:22PM +0100, Jakub Jelinek via Gcc-patches wrote:
>> On Mon, Nov 22, 2021 at 06:01:08PM +0530, Siddhesh Poyarekar wrote:
>>> On 11/22/21 17:30, Siddhesh Poyarekar wrote:
>>>> So I've got patch 10/10, which handles dynamic (and consequently
>>>> negative) offsets.  It basically computes a "whole size", which then
>>>> gives the extent to which a negative offset is valid, making the
>>>> estimates a bit more precise.  I didn't do it for static object sizes
>>>> because I didn't have time then, but I could add a patch 11/10 if the
>>>> idea sounds OK to you.
>>>
>>> ... or alternatively, I could bring the whole size idea into this tree
>>> conversion patch so that it handles all kinds of offsets.  That might even
>>> eliminate patch 10/10.  What would you prefer?
>>
>> Into this patch.
> 
> BTW, seems the current behavior is to punt on those "negative" values,
> we trigger
>    if (offset >= offset_limit)
> case for it and return unknown.

The current behaviour is actually inconsistent; for SSA names it punts 
for sizes greater than offset limit and for addr_expr it ends up with 
larger sizes.

Siddhesh