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libbpf: Handle non-standardly sized enums better in BTF-to-C dumper

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Turns out C allows to force enum to be 1-byte or 8-byte explicitly using
mode(byte) or mode(word), respecticely. Linux sources are using this in
some cases. This is imporant to handle correctly, as enum size
determines corresponding fields in a struct that use that enum type. And
if enum size is incorrect, this will lead to invalid struct layout. So
add mode(byte) and mode(word) attribute support to btf_dump APIs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20221212211505.558851-3-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2022-12-12 13:15:01 -08:00 committed by Daniel Borkmann
parent 872aec4b5f
commit 21a9a1bccc
1 changed files with 38 additions and 0 deletions
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38
tools/lib/bpf/btf_dump.c
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@ -13,6 +13,7 @@
#include <ctype.h>
#include <endian.h>
#include <errno.h>
#include <limits.h>
#include <linux/err.h>
#include <linux/btf.h>
#include <linux/kernel.h>
@ -1076,6 +1077,43 @@ static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id,
else
btf_dump_emit_enum64_val(d, t, lvl, vlen);
btf_dump_printf(d, "\n%s}", pfx(lvl));
/* special case enums with special sizes */
if (t->size == 1) {
/* one-byte enums can be forced with mode(byte) attribute */
btf_dump_printf(d, " __attribute__((mode(byte)))");
} else if (t->size == 8 && d->ptr_sz == 8) {
/* enum can be 8-byte sized if one of the enumerator values
* doesn't fit in 32-bit integer, or by adding mode(word)
* attribute (but probably only on 64-bit architectures); do
* our best here to try to satisfy the contract without adding
* unnecessary attributes
*/
bool needs_word_mode;
if (btf_is_enum(t)) {
/* enum can't represent 64-bit values, so we need word mode */
needs_word_mode = true;
} else {
/* enum64 needs mode(word) if none of its values has
* non-zero upper 32-bits (which means that all values
* fit in 32-bit integers and won't cause compiler to
* bump enum to be 64-bit naturally
*/
int i;
needs_word_mode = true;
for (i = 0; i < vlen; i++) {
if (btf_enum64(t)[i].val_hi32 != 0) {
needs_word_mode = false;
break;
}
}
}
if (needs_word_mode)
btf_dump_printf(d, " __attribute__((mode(word)))");
}
}
static void btf_dump_emit_fwd_def(struct btf_dump *d, __u32 id,