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path: root/tools/lib/bpf/btf_dump.c
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Diffstat (limited to 'tools/lib/bpf/btf_dump.c')
-rw-r--r--tools/lib/bpf/btf_dump.c199
1 files changed, 148 insertions, 51 deletions
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index deb2bc9a0a7b..580985ee5545 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>
@@ -833,14 +834,9 @@ static bool btf_is_struct_packed(const struct btf *btf, __u32 id,
const struct btf_type *t)
{
const struct btf_member *m;
- int align, i, bit_sz;
+ int max_align = 1, align, i, bit_sz;
__u16 vlen;
- align = btf__align_of(btf, id);
- /* size of a non-packed struct has to be a multiple of its alignment*/
- if (align && t->size % align)
- return true;
-
m = btf_members(t);
vlen = btf_vlen(t);
/* all non-bitfield fields have to be naturally aligned */
@@ -849,8 +845,11 @@ static bool btf_is_struct_packed(const struct btf *btf, __u32 id,
bit_sz = btf_member_bitfield_size(t, i);
if (align && bit_sz == 0 && m->offset % (8 * align) != 0)
return true;
+ max_align = max(align, max_align);
}
-
+ /* size of a non-packed struct has to be a multiple of its alignment */
+ if (t->size % max_align != 0)
+ return true;
/*
* if original struct was marked as packed, but its layout is
* naturally aligned, we'll detect that it's not packed
@@ -858,44 +857,97 @@ static bool btf_is_struct_packed(const struct btf *btf, __u32 id,
return false;
}
-static int chip_away_bits(int total, int at_most)
-{
- return total % at_most ? : at_most;
-}
-
static void btf_dump_emit_bit_padding(const struct btf_dump *d,
- int cur_off, int m_off, int m_bit_sz,
- int align, int lvl)
+ int cur_off, int next_off, int next_align,
+ bool in_bitfield, int lvl)
{
- int off_diff = m_off - cur_off;
- int ptr_bits = d->ptr_sz * 8;
+ const struct {
+ const char *name;
+ int bits;
+ } pads[] = {
+ {"long", d->ptr_sz * 8}, {"int", 32}, {"short", 16}, {"char", 8}
+ };
+ int new_off, pad_bits, bits, i;
+ const char *pad_type;
+
+ if (cur_off >= next_off)
+ return; /* no gap */
+
+ /* For filling out padding we want to take advantage of
+ * natural alignment rules to minimize unnecessary explicit
+ * padding. First, we find the largest type (among long, int,
+ * short, or char) that can be used to force naturally aligned
+ * boundary. Once determined, we'll use such type to fill in
+ * the remaining padding gap. In some cases we can rely on
+ * compiler filling some gaps, but sometimes we need to force
+ * alignment to close natural alignment with markers like
+ * `long: 0` (this is always the case for bitfields). Note
+ * that even if struct itself has, let's say 4-byte alignment
+ * (i.e., it only uses up to int-aligned types), using `long:
+ * X;` explicit padding doesn't actually change struct's
+ * overall alignment requirements, but compiler does take into
+ * account that type's (long, in this example) natural
+ * alignment requirements when adding implicit padding. We use
+ * this fact heavily and don't worry about ruining correct
+ * struct alignment requirement.
+ */
+ for (i = 0; i < ARRAY_SIZE(pads); i++) {
+ pad_bits = pads[i].bits;
+ pad_type = pads[i].name;
- if (off_diff <= 0)
- /* no gap */
- return;
- if (m_bit_sz == 0 && off_diff < align * 8)
- /* natural padding will take care of a gap */
- return;
+ new_off = roundup(cur_off, pad_bits);
+ if (new_off <= next_off)
+ break;
+ }
- while (off_diff > 0) {
- const char *pad_type;
- int pad_bits;
-
- if (ptr_bits > 32 && off_diff > 32) {
- pad_type = "long";
- pad_bits = chip_away_bits(off_diff, ptr_bits);
- } else if (off_diff > 16) {
- pad_type = "int";
- pad_bits = chip_away_bits(off_diff, 32);
- } else if (off_diff > 8) {
- pad_type = "short";
- pad_bits = chip_away_bits(off_diff, 16);
- } else {
- pad_type = "char";
- pad_bits = chip_away_bits(off_diff, 8);
+ if (new_off > cur_off && new_off <= next_off) {
+ /* We need explicit `<type>: 0` aligning mark if next
+ * field is right on alignment offset and its
+ * alignment requirement is less strict than <type>'s
+ * alignment (so compiler won't naturally align to the
+ * offset we expect), or if subsequent `<type>: X`,
+ * will actually completely fit in the remaining hole,
+ * making compiler basically ignore `<type>: X`
+ * completely.
+ */
+ if (in_bitfield ||
+ (new_off == next_off && roundup(cur_off, next_align * 8) != new_off) ||
+ (new_off != next_off && next_off - new_off <= new_off - cur_off))
+ /* but for bitfields we'll emit explicit bit count */
+ btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type,
+ in_bitfield ? new_off - cur_off : 0);
+ cur_off = new_off;
+ }
+
+ /* Now we know we start at naturally aligned offset for a chosen
+ * padding type (long, int, short, or char), and so the rest is just
+ * a straightforward filling of remaining padding gap with full
+ * `<type>: sizeof(<type>);` markers, except for the last one, which
+ * might need smaller than sizeof(<type>) padding.
+ */
+ while (cur_off != next_off) {
+ bits = min(next_off - cur_off, pad_bits);
+ if (bits == pad_bits) {
+ btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type, pad_bits);
+ cur_off += bits;
+ continue;
+ }
+ /* For the remainder padding that doesn't cover entire
+ * pad_type bit length, we pick the smallest necessary type.
+ * This is pure aesthetics, we could have just used `long`,
+ * but having smallest necessary one communicates better the
+ * scale of the padding gap.
+ */
+ for (i = ARRAY_SIZE(pads) - 1; i >= 0; i--) {
+ pad_type = pads[i].name;
+ pad_bits = pads[i].bits;
+ if (pad_bits < bits)
+ continue;
+
+ btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type, bits);
+ cur_off += bits;
+ break;
}
- btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type, pad_bits);
- off_diff -= pad_bits;
}
}
@@ -915,9 +967,11 @@ static void btf_dump_emit_struct_def(struct btf_dump *d,
{
const struct btf_member *m = btf_members(t);
bool is_struct = btf_is_struct(t);
- int align, i, packed, off = 0;
+ bool packed, prev_bitfield = false;
+ int align, i, off = 0;
__u16 vlen = btf_vlen(t);
+ align = btf__align_of(d->btf, id);
packed = is_struct ? btf_is_struct_packed(d->btf, id, t) : 0;
btf_dump_printf(d, "%s%s%s {",
@@ -927,41 +981,47 @@ static void btf_dump_emit_struct_def(struct btf_dump *d,
for (i = 0; i < vlen; i++, m++) {
const char *fname;
- int m_off, m_sz;
+ int m_off, m_sz, m_align;
+ bool in_bitfield;
fname = btf_name_of(d, m->name_off);
m_sz = btf_member_bitfield_size(t, i);
m_off = btf_member_bit_offset(t, i);
- align = packed ? 1 : btf__align_of(d->btf, m->type);
+ m_align = packed ? 1 : btf__align_of(d->btf, m->type);
+
+ in_bitfield = prev_bitfield && m_sz != 0;
- btf_dump_emit_bit_padding(d, off, m_off, m_sz, align, lvl + 1);
+ btf_dump_emit_bit_padding(d, off, m_off, m_align, in_bitfield, lvl + 1);
btf_dump_printf(d, "\n%s", pfx(lvl + 1));
btf_dump_emit_type_decl(d, m->type, fname, lvl + 1);
if (m_sz) {
btf_dump_printf(d, ": %d", m_sz);
off = m_off + m_sz;
+ prev_bitfield = true;
} else {
m_sz = max((__s64)0, btf__resolve_size(d->btf, m->type));
off = m_off + m_sz * 8;
+ prev_bitfield = false;
}
+
btf_dump_printf(d, ";");
}
/* pad at the end, if necessary */
- if (is_struct) {
- align = packed ? 1 : btf__align_of(d->btf, id);
- btf_dump_emit_bit_padding(d, off, t->size * 8, 0, align,
- lvl + 1);
- }
+ if (is_struct)
+ btf_dump_emit_bit_padding(d, off, t->size * 8, align, false, lvl + 1);
/*
* Keep `struct empty {}` on a single line,
* only print newline when there are regular or padding fields.
*/
- if (vlen || t->size)
+ if (vlen || t->size) {
btf_dump_printf(d, "\n");
- btf_dump_printf(d, "%s}", pfx(lvl));
+ btf_dump_printf(d, "%s}", pfx(lvl));
+ } else {
+ btf_dump_printf(d, "}");
+ }
if (packed)
btf_dump_printf(d, " __attribute__((packed))");
}
@@ -1073,6 +1133,43 @@ 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,