Re: [PATCH v2] btf: Add support to BTF_KIND_ENUM64 type

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

On 9/29/22 17:35, Indu Bhagat wrote:
> On 9/28/22 2:15 PM, Guillermo E. Martinez via Gcc-patches wrote:
>> Hello GCC team,
>>
>> The following is patch v2 to update BTF/CTF backend supporting
>> BTF_KIND_ENUM64 type. Changes from v1:
>>
>>    + Fix typo in commit message.
>>    + Fix changelog entries.
>>
>> Comments will be welcomed and appreciated!,
>>
>> Kind regards,
>> guillermo
>> -- 
>>
> 
> Hi Guillermo,
> 

Hi Indu,

> Thanks for your patch.
> 
> Sorry for the delay in reviewing this patch. Please see my comments inlined.
> 

No worries, thanks so much for your comments!. They were really useful.

> Indu
> 
>> 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 in ctf_dtdef to represent specific type's properties, in
>> the particular case for CTF enums it helps to distinguish when its
>> enumerators values are signed or unsigned, 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 enumerators sign,
>>     using correct BPF type in BTF_KIND_ENUMi{,64}.
> 
> Typo : i after ENUM
> 

Fixed in v3.

>>     (btf_asm_enum_const): New argument to represent the size of
>>     the BTF enum type.
>>     * ctfc.cc (ctf_add_enum): Use and initialization of flag field to
>>     CTF_ENUM_F_NONE.
>>     (ctf_add_enumerator): New argument to represent CTF flags,
>>     updating the comment and flag vaue according to enumerators
>>     sing.
>>     * ctfc.h (ctf_dmdef): Update dmd_value to HOST_WIDE_INT to allow
>>     use 32/64 bits enumerators.
>>     (ctf_dtdef): Add flags to to describe specific type's properties.
>>     * dwarf2ctf.cc (gen_ctf_enumeration_type): Update flags field
>>     depending when a signed enumerator value is found.
>>
>> 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-enum64-1.c: New testcase.
>> ---
>>   gcc/btfout.cc                                 | 24 ++++++++---
>>   gcc/ctfc.cc                                   | 14 ++++---
>>   gcc/ctfc.h                                    |  9 +++-
>>   gcc/dwarf2ctf.cc                              |  9 +++-
>>   gcc/testsuite/gcc.dg/debug/btf/btf-enum-1.c   |  2 +-
>>   gcc/testsuite/gcc.dg/debug/btf/btf-enum64-1.c | 41 +++++++++++++++++++
>>   include/btf.h                                 | 19 +++++++--
>>   7 files changed, 99 insertions(+), 19 deletions(-)
>>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-enum64-1.c
>>
>> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
>> index 997a33fa089..4b11c867c23 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->flags & CTF_ENUM_F_ENUMERATORS_SIGNED)
>> +            ? BTF_KF_ENUM_SIGNED
>> +            : BTF_KF_ENUM_UNSIGNED;
>> +     if (dtd->dtd_data.ctti_size == 0x8)
>> +       btf_kind = BTF_KIND_ENUM64;
>> +   }
>> +
> 
> See below. If you do add a new member in ctf_dmdef instead (as I propose), you should ideally iterate over the enumerators (dtd->dtd_u.dtu_members) to make sure they are all the same signedness.
> 

Correct, struct `ctf_dmdef' stores enumerator's information. However
in BTF spec ``info.kind_flag`` is not a property per enumerator, but
enumeration type property instead, so I decided to add in `ctf_dtdef'
a `flag' field to store the signeedness information for an enumeration
type, then in `gen_ctf_enumeration_type' when it builds the enumerators
entries,`ctf_dtdef.flag' is updated to `CTF_ENUM_F_ENUMERATORS_SIGNED'
when  it found a signed enumerator value meaning that enumeration type
should be consider a signed type. i.e, I detect signeedness when
enumeration type is being building.

Of course, I can add `dmd_value_signed' field in `ctf_dmdef' but I need
to iterate over all `ctf_dmdef.dmd_value_signed' (in `btf_asm_type' I guess)
to properly set ``info.kind_flag`` if it's a signed enumeration type.

>>     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 +719,13 @@ 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");
>> +  dw2_asm_output_data (size, dmd->dmd_value, "bte_value");
> 
> I am not sure if this is ok to do like the above. The format specification says:
> 
No, It is not right.

> The ``btf_enum64`` encoding:
>    * ``name_off``: offset to a valid C identifier
>    * ``val_lo32``: lower 32-bit value for a 64-bit value
>    * ``val_hi32``: high 32-bit value for a 64-bit value
> 
> What if the chosen BPF arch type is big-endian and the const value is 8 bytes ? Wouldnt such constant values to be written out incorrectly then ? I think you need to write the lower 32-bits and higher 32-bits explicitly to avoid that issue.
> 

Totally agree. Fixed in v3.

>>   }
>>   /* Asm'out a function parameter description following a BTF_KIND_FUNC_PROTO.  */
>> @@ -871,7 +883,7 @@ 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 +893,7 @@ 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..253c36b6a0a 100644
>> --- a/gcc/ctfc.cc
>> +++ b/gcc/ctfc.cc
>> @@ -604,6 +604,7 @@ ctf_add_enum (ctf_container_ref ctfc, uint32_t flag, const char * name,
>>     gcc_assert (size <= CTF_MAX_SIZE);
>>     dtd->dtd_data.ctti_size = size;
>> +  dtd->flags = CTF_ENUM_F_NONE;
>>     ctfc->ctfc_num_stypes++;
>> @@ -612,7 +613,7 @@ ctf_add_enum (ctf_container_ref ctfc, uint32_t flag, const char * name,
>>   int
>>   ctf_add_enumerator (ctf_container_ref ctfc, ctf_id_t enid, const char * name,
>> -            HOST_WIDE_INT value, dw_die_ref die)
>> +            HOST_WIDE_INT value, uint32_t flags, dw_die_ref die)
>>   {
>>     ctf_dmdef_t * dmd;
>>     uint32_t kind, vlen, root;
>> @@ -630,10 +631,12 @@ ctf_add_enumerator (ctf_container_ref ctfc, ctf_id_t enid, const char * name,
>>     gcc_assert (kind == CTF_K_ENUM && vlen < CTF_MAX_VLEN);
>> -  /* Enum value is of type HOST_WIDE_INT in the compiler, dmd_value is int32_t
>> -     on the other hand.  Check bounds and skip adding this enum value if out of
>> -     bounds.  */
>> -  if ((value > INT_MAX) || (value < INT_MIN))
>> +  /* Enum value is of type HOST_WIDE_INT in the compiler, CTF enumerators
>> +     values in ctf_enum_t is limited to int32_t, BTF supports signed and
>> +     unsigned enumerators values of 32 and 64 bits, for both debug formats
>> +     we use ctf_dmdef_t.dmd_value entry of HOST_WIDE_INT type. So check
>> +     CTF bounds and skip adding this enum value if out of bounds.  */
>> +  if (!btf_debuginfo_p() && ((value > INT_MAX) || (value < INT_MIN)))
>>       {
>>         /* FIXME - Note this TBD_CTF_REPRESENTATION_LIMIT.  */
>>         return (1);
>> @@ -649,6 +652,7 @@ ctf_add_enumerator (ctf_container_ref ctfc, ctf_id_t enid, const char * name,
>>     dmd->dmd_value = value;
>>     dtd->dtd_data.ctti_info = CTF_TYPE_INFO (kind, root, vlen + 1);
>> +  dtd->flags |= flags;
>>     ctf_dmd_list_append (&dtd->dtd_u.dtu_members, dmd);
>>     if ((name != NULL) && strcmp (name, ""))
>> diff --git a/gcc/ctfc.h b/gcc/ctfc.h
>> index bcf3a43ae1b..a22342b2610 100644
>> --- a/gcc/ctfc.h
>> +++ b/gcc/ctfc.h
>> @@ -125,6 +125,10 @@ typedef struct GTY (()) ctf_itype
>>   #define CTF_FUNC_VARARG 0x1
>> +/* Enum specific flags.  */
>> +#define CTF_ENUM_F_NONE                     (0)
>> +#define CTF_ENUM_F_ENUMERATORS_SIGNED       (1 << 0)
>> +
>>   /* Struct/union/enum member definition for CTF generation.  */
>>   typedef struct GTY ((chain_next ("%h.dmd_next"))) ctf_dmdef
>> @@ -133,7 +137,7 @@ typedef struct GTY ((chain_next ("%h.dmd_next"))) ctf_dmdef
>>     ctf_id_t dmd_type;        /* Type of this member (for sou).  */
>>     uint32_t dmd_name_offset;    /* Offset of the name in str table.  */
>>     uint64_t dmd_offset;        /* Offset of this member in bits (for sou).  */
>> -  int dmd_value;        /* Value of this member (for enum).  */
>> +  HOST_WIDE_INT dmd_value;    /* Value of this member (for enum).  */
>>     struct ctf_dmdef * dmd_next;    /* A list node.  */
>>   } ctf_dmdef_t;
> 
> I am wondering if you considered adding a member here instead - something like-
> 
> bool dmd_value_signed; /* Signedness for the enumerator.  */.
> 
> See comment below.
> 
>> @@ -162,6 +166,7 @@ struct GTY ((for_user)) ctf_dtdef
>>     bool from_global_func; /* Whether this type was added from a global
>>                   function.  */
>>     uint32_t linkage;           /* Used in function types.  0=local, 1=global.  */
>> +  uint32_t flags;             /* Flags to describe specific type's properties.  */
>>     union GTY ((desc ("ctf_dtu_d_union_selector (&%1)")))
>>     {
>>       /* struct, union, or enum.  */
> 
> Instead of carrying this information in ctf_dtdef which is the data structure for each type in CTF, how about adding a new member in struct ctf_dmdef? The "flags" member is meant for only enum types, and hence it will be more appropriate to add to ctf_dmdef as say, dmd_value_signed.
> 

Yes, `ctf_dtdef' is structure for each type in CTF (including enumeration),
and `ctf_dmdef' keeps information for enumerator, not for the enumeration type.

>> @@ -429,7 +434,7 @@ extern ctf_id_t ctf_add_sou (ctf_container_ref, uint32_t, const char *,
>>                    uint32_t, size_t, dw_die_ref);
>>   extern int ctf_add_enumerator (ctf_container_ref, ctf_id_t, const char *,
>> -                   HOST_WIDE_INT, dw_die_ref);
>> +                   HOST_WIDE_INT, uint32_t, dw_die_ref);
>>   extern int ctf_add_member_offset (ctf_container_ref, dw_die_ref, const char *,
>>                     ctf_id_t, uint64_t);
>>   extern int ctf_add_function_arg (ctf_container_ref, dw_die_ref,
>> diff --git a/gcc/dwarf2ctf.cc b/gcc/dwarf2ctf.cc
>> index 397100004c2..0ef96dd48fd 100644
>> --- a/gcc/dwarf2ctf.cc
>> +++ b/gcc/dwarf2ctf.cc
>> @@ -772,6 +772,7 @@ gen_ctf_enumeration_type (ctf_container_ref ctfc, dw_die_ref enumeration)
>>         const char *enumerator_name;
>>         dw_attr_node *enumerator_value;
>>         HOST_WIDE_INT value_wide_int;
>> +      uint32_t flags = 0;
>>         c = dw_get_die_sib (c);
>> @@ -785,10 +786,14 @@ gen_ctf_enumeration_type (ctf_container_ref ctfc, dw_die_ref enumeration)
>>             == dw_val_class_unsigned_const_implicit))
>>           value_wide_int = AT_unsigned (enumerator_value);
>>         else
>> -        value_wide_int = AT_int (enumerator_value);
>> +        {
>> +          value_wide_int = AT_int (enumerator_value);
>> +          flags |= CTF_ENUM_F_ENUMERATORS_SIGNED;
>> +        }
>>         ctf_add_enumerator (ctfc, enumeration_type_id,
>> -                  enumerator_name, value_wide_int, enumeration);
>> +                  enumerator_name, value_wide_int,
>> +                  flags, enumeration);
>>       }
>>         while (c != dw_get_die_child (enumeration));
>>     }
>> diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-enum-1.c b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-1.c
>> index 728493b0804..7e940529f1b 100644
>> --- a/gcc/testsuite/gcc.dg/debug/btf/btf-enum-1.c
>> +++ b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-1.c
>> @@ -4,7 +4,7 @@
>>   /* { dg-options "-O0 -gbtf -dA" } */
>>   /* { dg-final { scan-assembler-times "\[\t \]0x6000004\[\t \]+\[^\n\]*btt_info" 1 } } */
>> -/* { dg-final { scan-assembler-times "\[\t \]0x6000003\[\t \]+\[^\n\]*btt_info" 1 } } */
>> +/* { dg-final { scan-assembler-times "\[\t \]0x86000003\[\t \]+\[^\n\]*btt_info" 1 } } */
>>   /* { dg-final { scan-assembler-times "ascii \"QAD.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>>   /* { dg-final { scan-assembler-times "ascii \"QED.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>>   /* { dg-final { scan-assembler-times "ascii \"QOD.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-enum64-1.c b/gcc/testsuite/gcc.dg/debug/btf/btf-enum64-1.c
>> new file mode 100644
>> index 00000000000..da103842807
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/debug/btf/btf-enum64-1.c
>> @@ -0,0 +1,41 @@
>> +/* Test BTF generation for 64 bits enums.  */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-options "-O0 -gbtf -dA" } */
>> +
>> +/* { dg-final { scan-assembler-times "\[\t \].size\[\t \]myenum1,\[\t \]8" 1 } } */
>> +/* { dg-final { scan-assembler-times "\[\t \].size\[\t \]myenum2,\[\t \]8" 1 } } */
>> +/* { dg-final { scan-assembler-times "\[\t \].size\[\t \]myenum3,\[\t \]8" 1 } } */
>> +/* { dg-final { scan-assembler-times "\[\t \]0x13000003\[\t \]+\[^\n\]*btt_info" 2 } } */
>> +/* { dg-final { scan-assembler-times "\[\t \]0x93000003\[\t \]+\[^\n\]*btt_info" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"B1.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"B2.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"B3.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"C1.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"C2.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"C3.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"D1.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"D2.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "ascii \"D3.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
>> +/* { dg-final { scan-assembler-times "bte_value" 9 } } */
>> +
>> +enum default_enum
>> +{
>> +  B1 = 0xffffffffaa,
>> +  B2 = 0xbbbbbbbb,
>> +  B3 = 0xaabbccdd,
>> +} myenum1 = B1;
>> +
>> +enum explicit_unsigned
>> +{
>> +  C1 = 0xffffffffbbUL,
>> +  C2 = 0xbbbbbbbb,
>> +  C3 = 0xaabbccdd,
>> +} myenum2 = C1;
>> +
>> +enum signed64
>> +{
>> +  D1 = 0xffffffffaa,
>> +  D2 = 0xbbbbbbbb,
>> +  D3 = -0x1,
>> +} myenum3 = D1;
> 
> I wonder if its meaningul to add such an enum64 test with -mlittle-endian and -mbig-endian to keep the order of val_lo32 and val_hi32 tested.
> 

Very meaningful!. I'll add use cases in v3 for both endianess.

>> diff --git a/include/btf.h b/include/btf.h
>> index 78b551ced23..eba67f9d599 100644
>> --- a/include/btf.h
>> +++ b/include/btf.h
>> @@ -109,7 +109,8 @@ struct btf_type
>>   #define BTF_KIND_VAR        14    /* Variable.  */
>>   #define BTF_KIND_DATASEC    15    /* Section such as .bss or .data.  */
>>   #define BTF_KIND_FLOAT        16    /* Floating point.  */
>> -#define BTF_KIND_MAX        BTF_KIND_FLOAT
>> +#define BTF_KIND_ENUM64     19    /* Enumeration up to 64 bits.  */
>> +#define BTF_KIND_MAX        BTF_KIND_ENUM64
>>   #define NR_BTF_KINDS        (BTF_KIND_MAX + 1)
>>   /* For some BTF_KINDs, struct btf_type is immediately followed by
>> @@ -130,14 +131,17 @@ struct btf_type
>>   #define BTF_INT_BOOL    (1 << 2)
>>   /* BTF_KIND_ENUM is followed by VLEN struct btf_enum entries,
>> -   which describe the enumerators. Note that BTF currently only
>> -   supports signed 32-bit enumerator values.  */
>> +   which describe the enumerators. */
>>   struct btf_enum
>>   {
>>     uint32_t name_off;    /* Offset in string section of enumerator name.  */
>>     int32_t  val;        /* Enumerator value.  */
>>   };
>> +/* BTF_KF_ENUM_ holds the flags for kflags in BTF_KIND_ENUM{,64}.  */
>> +#define BTF_KF_ENUM_UNSIGNED    (0)
>> +#define BTF_KF_ENUM_SIGNED     (1 << 0)
>> +
>>   /* BTF_KIND_ARRAY is followed by a single struct btf_array.  */
>>   struct btf_array
>>   {
>> @@ -190,6 +194,15 @@ struct btf_var_secinfo
>>     uint32_t size;    /* Size (in bytes) of variable.  */
>>   };
>> +/* BTF_KIND_ENUM64 is followed by VLEN struct btf_enum64 entries,
>> +   which describe the 64 bits enumerators.  */
>> +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 */
>> +};
>> +
>>   #ifdef    __cplusplus
>>   }
>>   #endif
>>
>