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@xxxxxxxxxx>
---
tools/lib/bpf/btf_dump.c | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 69e80ee5f70e..234e82334d56 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -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,
--
2.30.2
