diff mbox series

Fixed problem with BTF defining smaller enums.

Message ID 20231113223739.11844-1-cupertino.miranda@oracle.com
State Unresolved
Headers
Series Fixed problem with BTF defining smaller enums. |

Checks

Context Check Description
snail/gcc-patch-check warning Git am fail log

Commit Message

Cupertino Miranda Nov. 13, 2023, 10:37 p.m. UTC 
  This patch fixes a BTF, which would become invalid when having
smaller then 4 byte definitions of enums.
For example, when using the __attribute__((mode(byte))) in the enum
definition.

Two problems were identified:
 - it would incorrectly create an entry for enum64 when the size of the
   enum was different then 4.
 - it would allocate less then 4 bytes for the value entry in BTF, in
   case the type was smaller.

BTF generated was validated against clang.

gcc/ChangeLog:
	* bpfout.cc (btf_calc_num_vbytes): Fixed logic for enum64.
	(btf_asm_enum_const): Corrected logic for enum64 and smaller
	than 4 bytes values.
---
 gcc/btfout.cc | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

Comments

David Faust Nov. 14, 2023, 4:28 p.m. UTC | #1 
Hi Cupertino,

A couple of comments inline.

On 11/13/23 14:37, Cupertino Miranda wrote:
> This patch fixes a BTF, which would become invalid when having
> smaller then 4 byte definitions of enums.
> For example, when using the __attribute__((mode(byte))) in the enum
> definition.

Please add a test for this case in the BTF testsuite.

> 
> Two problems were identified:
>  - it would incorrectly create an entry for enum64 when the size of the
>    enum was different then 4.
>  - it would allocate less then 4 bytes for the value entry in BTF, in
>    case the type was smaller.
> 
> BTF generated was validated against clang.
> 
> gcc/ChangeLog:
> 	* bpfout.cc (btf_calc_num_vbytes): Fixed logic for enum64.
> 	(btf_asm_enum_const): Corrected logic for enum64 and smaller
> 	than 4 bytes values.
> ---
>  gcc/btfout.cc | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
> index e07fed302c24..d2263ec6eec3 100644
> --- a/gcc/btfout.cc
> +++ b/gcc/btfout.cc
> @@ -299,7 +299,7 @@ btf_calc_num_vbytes (ctf_dtdef_ref dtd)
>        break;
>  
>      case BTF_KIND_ENUM:
> -      vlen_bytes += (dtd->dtd_data.ctti_size == 0x8)
> +      vlen_bytes += (dtd->dtd_data.ctti_size > 4)
>  			? vlen * sizeof (struct btf_enum64)
>  			: vlen * sizeof (struct btf_enum);
>        break;
> @@ -914,13 +914,13 @@ btf_asm_enum_const (unsigned int size, ctf_dmdef_t * dmd, unsigned int idx)
>  {
>    dw2_asm_output_data (4, dmd->dmd_name_offset, "ENUM_CONST '%s' idx=%u",
>  		       dmd->dmd_name, idx);
> -  if (size == 4)
> -    dw2_asm_output_data (size, dmd->dmd_value, "bte_value");
> -  else
> +  if (size > 4)
>      {
> -      dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
> +      dw2_asm_output_data (4, dmd->dmd_value & 0xfffffffe, "bte_value_lo32");

I don't understand the mask change here.
Why clear the low bit of the enum value?

>        dw2_asm_output_data (4, (dmd->dmd_value >> 32) & 0xffffffff, "bte_value_hi32");
>      }
> +  else
> +    dw2_asm_output_data (size < 4 ? 4 : size, dmd->dmd_value, "bte_value");

In the else case isn't size guaranteed <= 4?
In which case, 'size < 4 ? 4 : size' always evaluates to 4.
So I would suggest to just write a literal 4 to keep it simple.


>  }
>  
>  /* Asm'out a function parameter description following a BTF_KIND_FUNC_PROTO.  */
diff mbox series

Patch

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index e07fed302c24..d2263ec6eec3 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -299,7 +299,7 @@  btf_calc_num_vbytes (ctf_dtdef_ref dtd)
       break;
 
     case BTF_KIND_ENUM:
-      vlen_bytes += (dtd->dtd_data.ctti_size == 0x8)
+      vlen_bytes += (dtd->dtd_data.ctti_size > 4)
 			? vlen * sizeof (struct btf_enum64)
 			: vlen * sizeof (struct btf_enum);
       break;
@@ -914,13 +914,13 @@  btf_asm_enum_const (unsigned int size, ctf_dmdef_t * dmd, unsigned int idx)
 {
   dw2_asm_output_data (4, dmd->dmd_name_offset, "ENUM_CONST '%s' idx=%u",
 		       dmd->dmd_name, idx);
-  if (size == 4)
-    dw2_asm_output_data (size, dmd->dmd_value, "bte_value");
-  else
+  if (size > 4)
     {
-      dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
+      dw2_asm_output_data (4, dmd->dmd_value & 0xfffffffe, "bte_value_lo32");
       dw2_asm_output_data (4, (dmd->dmd_value >> 32) & 0xffffffff, "bte_value_hi32");
     }
+  else
+    dw2_asm_output_data (size < 4 ? 4 : size, dmd->dmd_value, "bte_value");
 }
 
 /* Asm'out a function parameter description following a BTF_KIND_FUNC_PROTO.  */