Re: [PATCH v3] btf: Add support to BTF_KIND_ENUM64 type

["Guillermo E. Martinez" <guillermo.e.martinez@oracle.com>]

On 10/18/22 16:40, Indu Bhagat wrote:
> Hi Guillermo,
> 

Hi Indu,

> On 10/14/22 8:55 PM, Guillermo E. Martinez wrote:
>> Hello,
>>
>> The following is patch v3 to update BTF/CTF backend supporting
>> BTF_KIND_ENUM64 type. Changes from v2:
>>
>>    + Add a new `dtd_enum_unsigned' field in `ctf_dtdef' to indicate
>>      signedness of the enum type.
>>    + Fix endianness for representing BTF enum 64-bits enumerators.
>>    + Add {little,big}-endian testcases.
>>
>> Comments will be welcomed and appreciated!,
>>
>> Kind regards,
>> guillermo
>>
>> -- 
>>
>> BTF supports 64-bits enumerators with following encoding:
>>
>>    struct btf_type:
>>      name_off: 0 or offset to a valid C identifier
>>      info.kind_flag: 0 for unsigned, 1 for signed
>>      info.kind: BTF_KIND_ENUM64
>>      info.vlen: number of enum values
>>      size: 1/2/4/8
>>
>> The btf_type is followed by info.vlen number of:
>>
>>      struct btf_enum64
>>      {
>>        uint32_t name_off;   /* Offset in string section of enumerator name.  */
>>        uint32_t val_lo32;   /* lower 32-bit value for a 64-bit value Enumerator */
>>        uint32_t val_hi32;   /* high 32-bit value for a 64-bit value Enumerator */
>>      };
>>
>> So, a new btf_enum64 structure was added to represent BTF_KIND_ENUM64
>> and a new field dtd_enum_unsigned in ctf_dtdef structure to distinguish
>> when CTF enum is a signed or unsigned type, later that information is
>> used to encode the BTF enum type.
>>
>> gcc/ChangeLog:
>>
>>     * btfout.cc (btf_calc_num_vbytes): Compute enumeration size depending of
>>     enumerator type btf_enum{,64}.
>>     (btf_asm_type): Update btf_kflag according to enumeration type sign
>>     using dtd_enum_unsigned field for both:  BTF_KIND_ENUM{,64}.
>>     (btf_asm_enum_const): New argument to represent the size of
>>     the BTF enum type, writing the enumerator constant value for
>>     32 bits, if it's 64 bits then explicitly writes lower 32-bits
>>     value and higher 32-bits value.
>>     (output_asm_btf_enum_list): Add enumeration size argument.
>>     * ctfc.cc (ctf_add_enum): New argument to represent CTF enum
>>     basic information.
>>     (ctf_add_generic): Use of ei_{name. size, unsigned} to build the
>>     dtd structure containing enumeration information.
>>     (ctf_add_enumerator): Update comment mention support for BTF
>>     enumeration in 64-bits.
>>     * ctfc.h (ctf_dmdef): Update dmd_value to HOST_WIDE_INT to allow
>>     use 32/64 bits enumerators.
>>     (ctf_enum_binfo): New type to represent CTF basic enum type
>>     information.
>>     (ctf_dtdef): New field to describe enum signedness.
>>     * dwarf2ctf.cc (gen_ctf_enumeration_type): Use of ctf_enum_binfo
>>     type to pass information to ctf_add_enum to build the enum type.
>>
>> include/
>>     * btf.h (btf_enum64): Add new definition and new symbolic
>>     constant to BTF_KIND_ENUM64 and BTF_KF_ENUM_{UN,}SIGNED.
>>
>> gcc/testsuite/ChangeLog:
>>
>>     * gcc.dg/debug/btf/btf-enum-1.c: Update testcase, with correct
>>     info.kflags encoding.
>>     * gcc.dg/debug/btf/btf-enum64-be-1.c: New testcase.
>>     * gcc.dg/debug/btf/btf-enum64-le-1.c: New testcase.
>> ---
>>   gcc/btfout.cc                                 | 30 ++++++++++---
>>   gcc/ctfc.cc                                   | 22 +++++-----
>>   gcc/ctfc.h                                    | 15 +++++--
>>   gcc/dwarf2ctf.cc                              |  8 +++-
>>   gcc/testsuite/gcc.dg/debug/btf/btf-enum-1.c   |  2 +-
>>   .../gcc.dg/debug/btf/btf-enum64-be-1.c        | 44 +++++++++++++++++++
>>   .../gcc.dg/debug/btf/btf-enum64-le-1.c        | 44 +++++++++++++++++++
>>   include/btf.h                                 | 19 ++++++--
>>   8 files changed, 160 insertions(+), 24 deletions(-)
>>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-enum64-be-1.c
>>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-enum64-le-1.c
>>
>> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
>> index 997a33fa089..aef9fd70a28 100644
>> --- a/gcc/btfout.cc
>> +++ b/gcc/btfout.cc
>> @@ -223,7 +223,9 @@ btf_calc_num_vbytes (ctf_dtdef_ref dtd)
>>         break;
>>       case BTF_KIND_ENUM:
>> -      vlen_bytes += vlen * sizeof (struct btf_enum);
>> +      vlen_bytes += (dtd->dtd_data.ctti_size == 0x8)
>> +            ? vlen * sizeof (struct btf_enum64)
>> +            : vlen * sizeof (struct btf_enum);
>>         break;
>>       case BTF_KIND_FUNC_PROTO:
>> @@ -622,6 +624,15 @@ btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>>         btf_size_type = 0;
>>       }
>> +  if (btf_kind == BTF_KIND_ENUM)
>> +    {
>> +      btf_kflag = dtd->dtd_enum_unsigned
>> +            ? BTF_KF_ENUM_UNSIGNED
>> +            : BTF_KF_ENUM_SIGNED;
>> +      if (dtd->dtd_data.ctti_size == 0x8)
>> +    btf_kind = BTF_KIND_ENUM64;
>> +   }
>> +
>>     dw2_asm_output_data (4, dtd->dtd_data.ctti_name, "btt_name");
>>     dw2_asm_output_data (4, BTF_TYPE_INFO (btf_kind, btf_kflag, btf_vlen),
>>                  "btt_info: kind=%u, kflag=%u, vlen=%u",
>> @@ -634,6 +645,7 @@ btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>>       case BTF_KIND_UNION:
>>       case BTF_KIND_ENUM:
>>       case BTF_KIND_DATASEC:
>> +    case BTF_KIND_ENUM64:
>>         dw2_asm_output_data (4, dtd->dtd_data.ctti_size, "btt_size: %uB",
>>                  dtd->dtd_data.ctti_size);
>>         return;
>> @@ -707,13 +719,19 @@ btf_asm_sou_member (ctf_container_ref ctfc, ctf_dmdef_t * dmd)
>>       }
>>   }
>> -/* Asm'out an enum constant following a BTF_KIND_ENUM.  */
>> +/* Asm'out an enum constant following a BTF_KIND_ENUM{,64}.  */
>>   static void
>> -btf_asm_enum_const (ctf_dmdef_t * dmd)
>> +btf_asm_enum_const (unsigned int size, ctf_dmdef_t * dmd)
>>   {
>>     dw2_asm_output_data (4, dmd->dmd_name_offset, "bte_name");
>> -  dw2_asm_output_data (4, dmd->dmd_value, "bte_value");
>> +  if (size == 4)
>> +    dw2_asm_output_data (size, dmd->dmd_value, "bte_value");
>> +  else
>> +    {
>> +      dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
>> +      dw2_asm_output_data (4, (dmd->dmd_value >> 32) & 0xffffffff, "bte_value_hi32");
>> +    }
>>   }
>>   /* Asm'out a function parameter description following a BTF_KIND_FUNC_PROTO.  */
>> @@ -871,7 +889,7 @@ output_asm_btf_sou_fields (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>>         btf_asm_sou_member (ctfc, dmd);
>>   }
>> -/* Output all enumerator constants following a BTF_KIND_ENUM.  */
>> +/* Output all enumerator constants following a BTF_KIND_ENUM{,64}.  */
>>   static void
>>   output_asm_btf_enum_list (ctf_container_ref ARG_UNUSED (ctfc),
>> @@ -881,7 +899,7 @@ output_asm_btf_enum_list (ctf_container_ref ARG_UNUSED (ctfc),
>>     for (dmd = dtd->dtd_u.dtu_members;
>>          dmd != NULL; dmd = (ctf_dmdef_t *) ctf_dmd_list_next (dmd))
>> -    btf_asm_enum_const (dmd);
>> +    btf_asm_enum_const (dtd->dtd_data.ctti_size, dmd);
>>   }
>>   /* Output all function arguments following a BTF_KIND_FUNC_PROTO.  */
>> diff --git a/gcc/ctfc.cc b/gcc/ctfc.cc
>> index 9773358a475..80322eea91a 100644
>> --- a/gcc/ctfc.cc
>> +++ b/gcc/ctfc.cc
>> @@ -576,8 +576,8 @@ ctf_add_array (ctf_container_ref ctfc, uint32_t flag, const ctf_arinfo_t * arp,
>>   }
>>   ctf_id_t
>> -ctf_add_enum (ctf_container_ref ctfc, uint32_t flag, const char * name,
>> -          HOST_WIDE_INT size, dw_die_ref die)
>> +ctf_add_enum (ctf_container_ref ctfc, uint32_t flag,
>> +          const ctf_enum_binfo_t *ei, dw_die_ref die)
> 
> The name and size information is typically being passed via explicit arguments in the other similar APIs in this functionality.  I have a slight preference towards keeping it that way when possible.  So in this API ctf_add_enum, how about just adding another function argument for signedness and getting rid of the data structure ctf_enum_binfo_t altogether. What do you think ?
> 

Sure!, I'll send the patch v4 with this change.

> Patch looks good to me otherwise.
>

Thanks for your comments,
  
> Thanks
> Indu
> 
>> [...]
Kind regards,
guillermo