[RFC v2] bpf.2: Use standard types and attributes

Alejandro Colomar
2021-05-04T11:05:48Z

Some manual pages are already using C99 syntax for integral
types 'uint32_t', but some aren't. There are some using kernel
syntax '__u32'. Fix those.

Some pages also document attributes, using GNU syntax
'__attribute__((xxx))'. Update those to use the shorter and more
portable C11 keywords such as 'alignas()' when possible, and C2x
syntax '[[gnu::xxx]]' elsewhere, which hasn't been standardized
yet, but is already implemented in GCC, and available through
either --std=c2x or any of the --std=gnu... options.

The standard isn't very clear on how to use alignas() or
[[]]-style attributes, so the following link is useful in the case
of 'alignas()' and '[[gnu::aligned()]]':
<https://stackoverflow.com/q/67271825/6872717>

Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: glibc <libc-alpha@sourceware.org>
Cc: GCC <gcc-patches@gcc.gnu.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: bpf <bpf@vger.kernel.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Zack Weinberg <zackw@panix.com>
Cc: Joseph Myers <joseph@codesourcery.com>
---
man2/bpf.2 | 49 ++++++++++++++++++++++++-------------------------
1 file changed, 24 insertions(+), 25 deletions(-)

diff --git a/man2/bpf.2 b/man2/bpf.2
index 6e1ffa198..04b8fbcef 100644
--- a/man2/bpf.2
+++ b/man2/bpf.2
@@ -186,41 +186,40 @@ commands:
.PP
.in +4n
.EX
-union bpf_attr {
+union [[gnu::aligned(8)]] bpf_attr {
struct { /* Used by BPF_MAP_CREATE */
- __u32 map_type;
- __u32 key_size; /* size of key in bytes */
- __u32 value_size; /* size of value in bytes */
- __u32 max_entries; /* maximum number of entries
- in a map */
+ uint32_t map_type;
+ uint32_t key_size; /* size of key in bytes */
+ uint32_t value_size; /* size of value in bytes */
+ uint32_t max_entries; /* maximum number of entries
+ in a map */
};

- struct { /* Used by BPF_MAP_*_ELEM and BPF_MAP_GET_NEXT_KEY
- commands */
- __u32 map_fd;
- __aligned_u64 key;
+ struct { /* Used by BPF_MAP_*_ELEM and BPF_MAP_GET_NEXT_KEY commands */
+ uint32_t map_fd;
+ uint64_t alignas(8) key;
union {
- __aligned_u64 value;
- __aligned_u64 next_key;
+ uint64_t alignas(8) value;
+ uint64_t alignas(8) next_key;
};
- __u64 flags;
+ uint64_t flags;
};

struct { /* Used by BPF_PROG_LOAD */
- __u32 prog_type;
- __u32 insn_cnt;
- __aligned_u64 insns; /* \(aqconst struct bpf_insn *\(aq */
- __aligned_u64 license; /* \(aqconst char *\(aq */
- __u32 log_level; /* verbosity level of verifier */
- __u32 log_size; /* size of user buffer */
- __aligned_u64 log_buf; /* user supplied \(aqchar *\(aq
- buffer */
- __u32 kern_version;
- /* checked when prog_type=kprobe
- (since Linux 4.1) */
+ uint32_t prog_type;
+ uint32_t insn_cnt;
+ uint64_t alignas(8) insns; /* \(aqconst struct bpf_insn *\(aq */
+ uint64_t alignas(8) license; /* \(aqconst char *\(aq */
+ uint32_t log_level; /* verbosity level of verifier */
+ uint32_t log_size; /* size of user buffer */
+ uint64_t alignas(8) log_buf; /* user supplied \(aqchar *\(aq
+ buffer */
+ uint32_t kern_version;
+ /* checked when prog_type=kprobe
+ (since Linux 4.1) */
.\" commit 2541517c32be2531e0da59dfd7efc1ce844644f5
};
-} __attribute__((aligned(8)));
+};
.EE
.in
.\"
--
2.31.1