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libctf: create: struct/union addition

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There's one API addition here: the existing CTF_ADD_ROOT / CTF_ADD_NONROOT
flags can have a new flag ORed with them, CTF_ADD_STRUCT_BITFIELDS,
indicating that the newly-added struct/union is capable of having bitfields
added to it via the new ctf_add_member_bitfield function (see a later
commit).

Without this, you can only add bitfields via the deprecated slice or base
type encoding representations (the former will force CTF output).

Implementation notes: structs and unions are always added with a CTF_K_BIG
prefix: if promoting from a forward, one is added.  These are elided at
serialization time if they are not needed to encode this size of struct /
this number of members.  (This means you don't have to figure out in advance
if your struct will be too big for BTF: you can just add members to it,
and libctf will figure it out and upgrade the dict as needed, or tell you
it can't if you've forbidden such things.)

We take advantage of this to merge a couple of very similar functions,
saving a bit of code.
This commit is contained in:
Nick Alcock
2025-04-24 16:28:26 +01:00
parent d5bb2772c6
commit cd8ea31666
2 changed files with 58 additions and 77 deletions
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17
include/ctf-api.h
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@@ -250,7 +250,9 @@ typedef struct ctf_snapshot_id
_CTF_ITEM (ECTF_UNSTABLE, "Attempt to write unstable file format version: set I_KNOW_LIBCTF_IS_UNSTABLE in the environment.") \
_CTF_ITEM (ECTF_HASPARENT, "Cannot ctf_import: dict already has a parent.") \
_CTF_ITEM (ECTF_WRONGPARENT, "Cannot ctf_import: incorrect parent provided.") \
_CTF_ITEM (ECTF_NOTSERIALIZED, "CTF dict must be serialized first.")
_CTF_ITEM (ECTF_NOTSERIALIZED, "CTF dict must be serialized first.") \
_CTF_ITEM (ECTF_NOTBITSOU, "Type is not a bitfield-capable struct or union.") \
_CTF_ITEM (ECTF_DESCENDING, "Structure offsets may not descend.") \
#define ECTF_BASE 1000 /* Base value for libctf errnos. */
@@ -284,6 +286,7 @@ _CTF_ERRORS
#define CTF_ADD_NONROOT 0 /* Type only visible in nested scope. */
#define CTF_ADD_ROOT 1 /* Type visible at top-level scope. */
#define CTF_ADD_STRUCT_BITFIELDS 2 /* Struct/union field-level bitfields */
/* Flags for ctf_member_next. */
@@ -842,13 +845,15 @@ extern ctf_id_t ctf_add_restrict (ctf_dict_t *, uint32_t, ctf_id_t);
/* Struct and union addition. Straight addition uses possibly-confusing rules
to guess the final size of the struct/union given its members: to explicitly
state the size of the struct or union (to report compiler-generated padding,
etc) use the _sized variants. */
etc) use the _sized variants. The FLAG parameter can take the value
CTF_ADD_STRUCT_BITFIELDS, indicating that bitfields can be directly added
to this struct via ctf_add_member_bitfield. */
extern ctf_id_t ctf_add_struct (ctf_dict_t *, uint32_t, const char *);
extern ctf_id_t ctf_add_union (ctf_dict_t *, uint32_t, const char *);
extern ctf_id_t ctf_add_struct_sized (ctf_dict_t *, uint32_t, const char *,
extern ctf_id_t ctf_add_struct (ctf_dict_t *, uint32_t flag, const char *);
extern ctf_id_t ctf_add_union (ctf_dict_t *, uint32_t flag, const char *);
extern ctf_id_t ctf_add_struct_sized (ctf_dict_t *, uint32_t flag, const char *,
size_t);
extern ctf_id_t ctf_add_union_sized (ctf_dict_t *, uint32_t, const char *,
extern ctf_id_t ctf_add_union_sized (ctf_dict_t *, uint32_t flag, const char *,
size_t);
/* Note that CTF cannot encode a given type. This usually returns an