[PATCH] Fixed problem with BTF defining smaller enums.

[PATCH] Fixed problem with BTF defining smaller enums.

[Cupertino Miranda]

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(-)

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.  */
-- 
2.30.2

Re: [PATCH] Fixed problem with BTF defining smaller enums.

[David Faust]

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.  */

[PATCH v2] Fixed problem with BTF defining smaller enums.

[Cupertino Miranda]

[-- Attachment #1: Type: text/plain, Size: 274 bytes --]


Hi everyone,

David: Thanks for the v1 review.

This version adds the following;
 - test case,
 - improves condition logic,
 - fixes mask typo.

Looking forward to your review.

v1 at: https://gcc.gnu.org/pipermail/gcc-patches/2023-November/636391.html

Cheers,
Cupertino


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: 0004-Fixed-problem-with-BTF-defining-smaller-enums.patch --]
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commit 3f89d352a4ee90882089142d743f8a748013b5fe
Author: Cupertino Miranda <cupertino.miranda@oracle.com>
Date:   Fri Nov 10 14:02:30 2023 +0000

    Fixed problem with BTF defining smaller enums.
    
    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/testsuite/ChangeLog:
            gcc.dg/debug/btf/btf-enum-small.c: Added test.

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index e07fed302c24..5f2e99ce4725 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;
@@ -914,8 +914,8 @@ 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");
+  if (size <= 4)
+    dw2_asm_output_data (size < 4 ? 4 : size, dmd->dmd_value, "bte_value");
   else
     {
       dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
new file mode 100644
index 000000000000..eb8a1bd2c438
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
@@ -0,0 +1,28 @@
+/* Test BTF generation for small enums.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -gbtf -dA" } */
+
+/* { dg-final { scan-assembler-not "bte_value_lo32" } } */
+/* { dg-final { scan-assembler-not "bte_value_hi32" } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x6000002\[\t \]+\[^\n\]*btt_info" 1 } } */
+/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALL' idx=0" 1 } } */
+/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALLY' idx=1" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"eSMALL.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"eSMALLY.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
+/* { dg-final { scan-assembler-times "bte_value" 2 } } */
+
+enum smalled_enum
+{
+  eSMALL,
+  eSMALLY,
+} __attribute__((mode(byte)));
+
+struct root_struct {
+  enum smalled_enum esmall;
+};
+
+enum smalled_enum
+foo(struct root_struct *root) {
+  return root->esmall;
+}

Re: [PATCH v2] Fixed problem with BTF defining smaller enums.

[David Faust]

Hi Cupertino,

On 11/27/23 09:21, Cupertino Miranda wrote:
> Hi everyone,
> 
> David: Thanks for the v1 review.
> 
> This version adds the following;
>  - test case,
>  - improves condition logic,
>  - fixes mask typo.
> 
> Looking forward to your review.

v2 LGTM, please apply.
Thanks!

> 
> v1 at: https://gcc.gnu.org/pipermail/gcc-patches/2023-November/636391.html
> 
> Cheers,
> Cupertino
> 
> 
> 0004-Fixed-problem-with-BTF-defining-smaller-enums.patch
> 
> commit 3f89d352a4ee90882089142d743f8a748013b5fe
> Author: Cupertino Miranda <cupertino.miranda@oracle.com>
> Date:   Fri Nov 10 14:02:30 2023 +0000
> 
>     Fixed problem with BTF defining smaller enums.
>     
>     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/testsuite/ChangeLog:
>             gcc.dg/debug/btf/btf-enum-small.c: Added test.
> 
> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
> index e07fed302c24..5f2e99ce4725 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;
> @@ -914,8 +914,8 @@ 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");
> +  if (size <= 4)
> +    dw2_asm_output_data (size < 4 ? 4 : size, dmd->dmd_value, "bte_value");
>    else
>      {
>        dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
> diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
> new file mode 100644
> index 000000000000..eb8a1bd2c438
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
> @@ -0,0 +1,28 @@
> +/* Test BTF generation for small enums.  */
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -gbtf -dA" } */
> +
> +/* { dg-final { scan-assembler-not "bte_value_lo32" } } */
> +/* { dg-final { scan-assembler-not "bte_value_hi32" } } */
> +/* { dg-final { scan-assembler-times "\[\t \]0x6000002\[\t \]+\[^\n\]*btt_info" 1 } } */
> +/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALL' idx=0" 1 } } */
> +/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALLY' idx=1" 1 } } */
> +/* { dg-final { scan-assembler-times "ascii \"eSMALL.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
> +/* { dg-final { scan-assembler-times "ascii \"eSMALLY.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
> +/* { dg-final { scan-assembler-times "bte_value" 2 } } */
> +
> +enum smalled_enum
> +{
> +  eSMALL,
> +  eSMALLY,
> +} __attribute__((mode(byte)));
> +
> +struct root_struct {
> +  enum smalled_enum esmall;
> +};
> +
> +enum smalled_enum
> +foo(struct root_struct *root) {
> +  return root->esmall;
> +}
> 

Re: [PATCH v2] Fixed problem with BTF defining smaller enums.

[Cupertino Miranda]

Thanks! Committed!

David Faust writes:

> Hi Cupertino,
>
> On 11/27/23 09:21, Cupertino Miranda wrote:
>> Hi everyone,
>>
>> David: Thanks for the v1 review.
>>
>> This version adds the following;
>>  - test case,
>>  - improves condition logic,
>>  - fixes mask typo.
>>
>> Looking forward to your review.
>
> v2 LGTM, please apply.
> Thanks!
>
>>
>> v1 at: https://gcc.gnu.org/pipermail/gcc-patches/2023-November/636391.html
>>
>> Cheers,
>> Cupertino
>>
>>
>> 0004-Fixed-problem-with-BTF-defining-smaller-enums.patch
>>
>> commit 3f89d352a4ee90882089142d743f8a748013b5fe
>> Author: Cupertino Miranda <cupertino.miranda@oracle.com>
>> Date:   Fri Nov 10 14:02:30 2023 +0000
>>
>>     Fixed problem with BTF defining smaller enums.
>>
>>     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/testsuite/ChangeLog:
>>             gcc.dg/debug/btf/btf-enum-small.c: Added test.
>>
>> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
>> index e07fed302c24..5f2e99ce4725 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;
>> @@ -914,8 +914,8 @@ 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");
>> +  if (size <= 4)
>> +    dw2_asm_output_data (size < 4 ? 4 : size, dmd->dmd_value, "bte_value");
>>    else
>>      {
>>        dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
>> diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
>> new file mode 100644
>> index 000000000000..eb8a1bd2c438
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
>> @@ -0,0 +1,28 @@
>> +/* Test BTF generation for small enums.  */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -gbtf -dA" } */
>> +
>> +/* { dg-final { scan-assembler-not "bte_value_lo32" } } */
>> +/* { dg-final { scan-assembler-not "bte_value_hi32" } } */
>> +/* { dg-final { scan-assembler-times "\[\t \]0x6000002\[\t \]+\[^\n\]*btt_info" 1 } } */
>> +/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALL' idx=0" 1 } } */
>> +/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALLY' idx=1" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"eSMALL.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"eSMALLY.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "bte_value" 2 } } */
>> +
>> +enum smalled_enum
>> +{
>> +  eSMALL,
>> +  eSMALLY,
>> +} __attribute__((mode(byte)));
>> +
>> +struct root_struct {
>> +  enum smalled_enum esmall;
>> +};
>> +
>> +enum smalled_enum
>> +foo(struct root_struct *root) {
>> +  return root->esmall;
>> +}
>>