On Tue, Mar 17, 2020 at 11:09:24PM -0700, Andrii Nakryiko wrote:

On Tue, Mar 17, 2020 at 8:15 PM Martin KaFai Lau [off-list ref] wrote:

quoted

This patch prints the enum's name if there is one found in
the array of btf_enum.

The commit 9eea98497951 ("bpf: fix BTF verification of enums")
has details about an enum could have any power-of-2 size (up to 8 bytes).
This patch also takes this chance to accommodate these non 4 byte
enums.

Acked-by: Quentin Monnet <redacted>
Signed-off-by: Martin KaFai Lau <redacted>
---
 tools/bpf/bpftool/btf_dumper.c | 39 +++++++++++++++++++++++++++++++---
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
index 01cc52b834fa..079f9171b1a3 100644
--- a/tools/bpf/bpftool/btf_dumper.c
+++ b/tools/bpf/bpftool/btf_dumper.c

@@ -43,9 +43,42 @@ static int btf_dumper_modifier(const struct btf_dumper *d, __u32 type_id,
        return btf_dumper_do_type(d, actual_type_id, bit_offset, data);
 }

-static void btf_dumper_enum(const void *data, json_writer_t *jw)
+static void btf_dumper_enum(const struct btf_dumper *d,
+                           const struct btf_type *t,
+                           const void *data)
 {
-       jsonw_printf(jw, "%d", *(int *)data);
+       const struct btf_enum *enums = btf_enum(t);
+       __s64 value;
+       __u16 i;
+
+       switch (t->size) {
+       case 8:
+               value = *(__s64 *)data;
+               break;
+       case 4:
+               value = *(__s32 *)data;
+               break;
+       case 2:
+               value = *(__s16 *)data;
+               break;
+       case 1:
+               value = *(__s8 *)data;
+               break;
+       default:
+               jsonw_string(d->jw, "<invalid_enum_size>");

Why not return error and let it propagate, similar to how
btf_dumper_array() can return an error? BTF is malformed if this
happened, so there is no point in continuing dumping, it's most
probably going to be a garbage.

I can send v4 to return -EINVAL here.

However, the caller of btf_dump*() is pretty loose on checking it.
It won't be difficult to find other existing codes that will
continue on btf_type's related error cases.  I also don't
think fixing all these error checking/returning is the
right answer here

The proper place to check malformed BTF is in btf__new().
Check it once there like how the kernel does.
[ btw, the data and btf here are obtained from the kernel
  which has verified it ].

quoted

+               return;
+       }
+
+       for (i = 0; i < btf_vlen(t); i++) {
+               if (value == enums[i].val) {
+                       jsonw_string(d->jw,
+                                    btf__name_by_offset(d->btf,
+                                                        enums[i].name_off));

nit: local variable will make it cleaner

I prefer to keep it as is.  There are many other uses like this.

quoted

+                       return;
+               }
+       }
+
+       jsonw_int(d->jw, value);
 }

 static int btf_dumper_array(const struct btf_dumper *d, __u32 type_id,

@@ -366,7 +399,7 @@ static int btf_dumper_do_type(const struct btf_dumper *d, __u32 type_id,
        case BTF_KIND_ARRAY:
                return btf_dumper_array(d, type_id, data);
        case BTF_KIND_ENUM:
-               btf_dumper_enum(data, d->jw);
+               btf_dumper_enum(d, t, data);
                return 0;
        case BTF_KIND_PTR:
                btf_dumper_ptr(data, d->jw, d->is_plain_text);
--

2.17.1