On Thu, Sep 24, 2020 at 8:21 AM John Fastabend [off-list ref] wrote:

Andrii Nakryiko wrote:

quoted

Refactor internals of struct btf to remove assumptions that BTF header, type
data, and string data are layed out contiguously in a memory in a single
memory allocation. Now we have three separate pointers pointing to the start
of each respective are: header, types, strings. In the next patches, these
pointers will be re-assigned to point to independently allocated memory areas,
if BTF needs to be modified.

Signed-off-by: Andrii Nakryiko <redacted>
---

[...]

quoted

--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c

@@ -27,18 +27,37 @@
 static struct btf_type btf_void;

 struct btf {
-     union {
-             struct btf_header *hdr;
-             void *data;
-     };
+     void *raw_data;
+     __u32 raw_size;
+
+     /*
+      * When BTF is loaded from ELF or raw memory it is stored
+      * in contiguous memory block, pointed to by raw_data pointer, and
+      * hdr, types_data, and strs_data point inside that memory region to
+      * respective parts of BTF representation:

I find the above comment a bit confusing. The picture though is great. How
about something like,

  When BTF is loaded from an ELF or raw memory it is stored
  in a continguous memory block. The hdr, type_data, and strs_data
  point inside that memory region to their respective parts of BTF
  representation

Had to do a mental diff to find the part you didn't like :) I'll
update the comment as you suggested.

quoted

+      *
+      * +--------------------------------+
+      * |  Header  |  Types  |  Strings  |
+      * +--------------------------------+
+      * ^          ^         ^
+      * |          |         |
+      * hdr        |         |
+      * types_data-+         |
+      * strs_data------------+
+      */
+     struct btf_header *hdr;
+     void *types_data;
+     void *strs_data;
+
+     /* type ID to `struct btf_type *` lookup index */
      __u32 *type_offs;
      __u32 type_offs_cap;
-     const char *strings;
-     void *nohdr_data;
-     void *types_data;
      __u32 nr_types;
-     __u32 data_size;
+
+     /* BTF object FD, if loaded into kernel */
      int fd;
+
+     /* Pointer size (in bytes) for a target architecture of this BTF */
      int ptr_sz;
 };

Thanks,
John