On 8/22/25 23:49, Indu Bhagat wrote:
> On 8/6/25 9:26 AM, David Faust wrote:
>> CTF array encoding uses uint32 for number of elements. This means there
>> is a hard upper limit on array types which the format can represent.
>>
>
> Hi David,
>
> Thanks for the patch.
>
> Few nits. But otherwise the patch looks good. As you noted in the
> bugzilla, more fixes will be needed to fix the ctf_die_bitsize () return
> type and its consumers...
Just to clarify, OK to push with the nits below addressed?
(I'll follow up with the other fixes mentioned in the PR soon, just
been a little sidetracked recently)
>
>> GCC internally was also using a uint32_t for this, which would overflow
>> when translating from DWARF for arrays with more with more than
>
> typo: "with more with more"
Oops. Thanks.
>
>> UINT32_MAX elements. Use an unsigned HOST_WIDE_INT instead to fetch
>> the array bound, and fall back to CTF_K_UNKNOWN if the array cannot
>> be represented in CTF.
>>
>> Tested on x86_64-pc-linux-gnu.
>>
>> PR debug/121411
>>
>> gcc/
>>
>> * dwarf2ctf.cc (gen_ctf_subrange_type): Use unsigned HWI for
>> array_num_elements. Fallback to CTF_K_UNKNOWN if the array
>> type has too many elements for CTF to represent.
>>
>> gcc/testsuite/
>>
>> * gcc.dg/debug/ctf/ctf-array-7.c: New test.
>> ---
>> gcc/dwarf2ctf.cc | 12 +++++++---
>> gcc/testsuite/gcc.dg/debug/ctf/ctf-array-7.c | 23 ++++++++++++++++++++
>> 2 files changed, 32 insertions(+), 3 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.dg/debug/ctf/ctf-array-7.c
>>
>> diff --git a/gcc/dwarf2ctf.cc b/gcc/dwarf2ctf.cc
>> index 7de3696a4d7..b0ad18a556c 100644
>> --- a/gcc/dwarf2ctf.cc
>> +++ b/gcc/dwarf2ctf.cc
>> @@ -361,7 +361,7 @@ gen_ctf_subrange_type (ctf_container_ref ctfc,
>> ctf_dtdef_ref array_elems_type,
>>
>> dw_attr_node *upper_bound_at;
>> dw_die_ref array_index_type;
>> - uint32_t array_num_elements;
>> + unsigned HOST_WIDE_INT array_num_elements;
>>
>> if (dw_get_die_tag (c) == DW_TAG_subrange_type)
>> {
>> @@ -376,9 +376,9 @@ gen_ctf_subrange_type (ctf_container_ref ctfc,
>> ctf_dtdef_ref array_elems_type,
>> if (upper_bound_at
>> && AT_class (upper_bound_at) == dw_val_class_unsigned_const)
>> /* This is the upper bound index. */
>> - array_num_elements = get_AT_unsigned (c, DW_AT_upper_bound) + 1;
>> + array_num_elements = AT_unsigned (get_AT (c, DW_AT_upper_bound)) + 1;
>> else if (get_AT (c, DW_AT_count))
>> - array_num_elements = get_AT_unsigned (c, DW_AT_count);
>> + array_num_elements = AT_unsigned (get_AT (c, DW_AT_count));
>> else
>> {
>> /* This is a VLA of some kind. */
>> @@ -388,6 +388,12 @@ gen_ctf_subrange_type (ctf_container_ref ctfc,
>> ctf_dtdef_ref array_elems_type,
>> else
>> gcc_unreachable ();
>>
>> + if (array_num_elements > UINT32_MAX)
>> + {
>> + /* The array cannot be encoded in CTF. */
>> + return gen_ctf_unknown_type (ctfc);
>> + }
>> +
>
> Is it possible to annotate this with "TBD_CTF_REPRESENTATION_LIMIT" in
> the comment ?
Sure, as a marker for the future right? Will add it.
/* The array cannot be encoded in CTF. TBD_CTF_REPRESENTATION_LIMIT. */
>
>> /* Ok, mount and register the array type. Note how the array
>> type we register here is the type of the elements in
>> subsequent "dimensions", if there are any. */
>> diff --git a/gcc/testsuite/gcc.dg/debug/ctf/ctf-array-7.c
>> b/gcc/testsuite/gcc.dg/debug/ctf/ctf-array-7.c
>> new file mode 100644
>> index 00000000000..01accc7c18f
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/debug/ctf/ctf-array-7.c
>> @@ -0,0 +1,23 @@
>> +/* CTF generation for array which cannot be encoded in CTF.
>> +
>> + CTF encoding uses a uint32 for number of elements in an array which
>> + means there is a hard upper limit on sizes of arrays which can be
>> + represented. Arrays with too many elements are encoded with
>> + CTF_K_UNKNOWN to indicate that they cannot be represented. */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-options "-O0 -gctf -dA" } */
>> +
>> +int rep[0xffffffff];
>> +int unrep[0x100000000];
>> +
>> +/* One dimension can be represented, other cannot.
>> + Result is a (representable) array with unknown element type. */
>> +int unrepdim [0xab][0x100000007];
>> +
>> +/* Two CTF_K_ARRAY, one (shared) CTF_K_UNKNOWN. */
>> +/* { dg-final { scan-assembler-times "0x12000000\[\t \]+\[^\n\]*ctt_info" 2
>> } } */
>> +/* { dg-final { scan-assembler-times "0x2000000\[\t \]+\[^\n\]*ctt_info" 1
>> } } */
>> +
>> +/* { dg-final { scan-assembler-times "\[\t \]+0xffffffff\[\t
>> \]+\[^\n\]*cta_nelems" 1 } } */
>> +/* { dg-final { scan-assembler-times "\[\t \]+0xab\[\t
>> \]+\[^\n\]*cta_nelems" 1 } } */
>
