Re: [PATCH 3/3] bpf: Corrected index computation when present with unnamed struct fields

[David Faust <david.faust@oracle.com>]

On 3/13/24 07:24, Cupertino Miranda wrote:
> Any unnamed structure field if not a member of the BTF_KIND_STRUCT.
typo: if -> is

I'd suggest to clarify that "any unnamed structure field" is really
any unnamed non-struct-or-union field, since anonymous inner structs
and unions certainly are present in BTF (and you handle them here).

> For that reason, CO-RE access strings indexes should take that in
> consideration. This patch adds a condition to the incrementer that
> computes the index for the field access.

Otherwise, OK.
Thanks.

> 
> gcc/ChangeLog:
> 	* config/bpf/core-builtins.cc (bpf_core_get_index): Check if
> 	field contains a DECL_NAME.
> 
> gcc/testsuite/ChangeLog:
> 	* gcc.target/bpf/core-builtin-fieldinfo-offset-1.c: Add
> 	testcase for unnamed fields.
> ---
>  gcc/config/bpf/core-builtins.cc                        |  6 +++++-
>  .../gcc.target/bpf/core-builtin-fieldinfo-offset-1.c   | 10 ++++++++--
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/gcc/config/bpf/core-builtins.cc b/gcc/config/bpf/core-builtins.cc
> index 70b14e48e6e5..8333ad81d0e0 100644
> --- a/gcc/config/bpf/core-builtins.cc
> +++ b/gcc/config/bpf/core-builtins.cc
> @@ -553,7 +553,11 @@ bpf_core_get_index (const tree node, bool *valid)
>  	{
>  	  if (l == node)
>  	    return i;
> -	  i++;
> +	  /* Skip unnamed padding, not represented by BTF.  */
> +	  if (DECL_NAME(l) != NULL_TREE
> +	      || TREE_CODE (TREE_TYPE (l)) == UNION_TYPE
> +	      || TREE_CODE (TREE_TYPE (l)) == RECORD_TYPE)
> +	    i++;
>  	}
>      }
>    else if (code == ARRAY_REF || code == ARRAY_RANGE_REF || code == MEM_REF)
> diff --git a/gcc/testsuite/gcc.target/bpf/core-builtin-fieldinfo-offset-1.c b/gcc/testsuite/gcc.target/bpf/core-builtin-fieldinfo-offset-1.c
> index 27654205287d..8b1d8b012a2a 100644
> --- a/gcc/testsuite/gcc.target/bpf/core-builtin-fieldinfo-offset-1.c
> +++ b/gcc/testsuite/gcc.target/bpf/core-builtin-fieldinfo-offset-1.c
> @@ -14,6 +14,9 @@ struct T {
>    struct S s[2];
>    char c;
>    char d;
> +  int a: 1;
> +  int:31;
> +  int f;
>  };
>  
>  enum {
> @@ -38,7 +41,9 @@ unsigned int foo (struct T *t)
>    unsigned e1 = __builtin_preserve_field_info (bar()->d, FIELD_BYTE_OFFSET);
>    unsigned e2 = __builtin_preserve_field_info (bar()->s[1].a4, FIELD_BYTE_OFFSET);
>  
> -  return s0a1 + s0a4 + s0x + s1a1 + s1a4 + s1x + c + d + e1 + e2;
> +  unsigned f1 = __builtin_preserve_field_info (t->f, FIELD_BYTE_OFFSET);
> +
> +  return s0a1 + s0a4 + s0x + s1a1 + s1a4 + s1x + c + d + e1 + e2 + f1;
>  }
>  
>  /* { dg-final { scan-assembler-times "\[\t \]mov\[\t \]%r\[0-9\],4" 2 } } */
> @@ -65,5 +70,6 @@ unsigned int foo (struct T *t)
>  /* { dg-final { scan-assembler-times "bpfcr_astr_off \\(\"0:1:1:4\"\\)" 1 } } */
>  /* { dg-final { scan-assembler-times "bpfcr_astr_off \\(\"0:2\"\\)" 1 } } */
>  /* { dg-final { scan-assembler-times "bpfcr_astr_off \\(\"0:3\"\\)" 2 } } */
> +/* { dg-final { scan-assembler-times "bpfcr_astr_off \\(\"0:5\"\\)" 1 } } */
>  
> -/* { dg-final { scan-assembler-times "0\[\t \]+\[^\n\]*bpfcr_kind" 10 } } */
> +/* { dg-final { scan-assembler-times "0\[\t \]+\[^\n\]*bpfcr_kind" 11 } } */