Netdev Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Dave Marchevsky <davemarchevsky@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Yonghong Song <yhs@fb.com>,
<netdev@vger.kernel.org>, Dave Marchevsky <davemarchevsky@fb.com>
Subject: [PATCH v4 bpf-next 4/9] libbpf: Modify bpf_printk to choose helper based on arg count
Date: Thu, 2 Sep 2021 10:19:24 -0700 [thread overview]
Message-ID: <20210902171929.3922667-5-davemarchevsky@fb.com> (raw)
In-Reply-To: <20210902171929.3922667-1-davemarchevsky@fb.com>
Instead of being a thin wrapper which calls into bpf_trace_printk,
libbpf's bpf_printk convenience macro now chooses between
bpf_trace_printk and bpf_trace_vprintk. If the arg count (excluding
format string) is >3, use bpf_trace_vprintk, otherwise use the older
helper.
The motivation behind this added complexity - instead of migrating
entirely to bpf_trace_vprintk - is to maintain good developer experience
for users compiling against new libbpf but running on older kernels.
Users who are passing <=3 args to bpf_printk will see no change in their
bytecode.
__bpf_vprintk functions similarly to BPF_SEQ_PRINTF and BPF_SNPRINTF
macros elsewhere in the file - it allows use of bpf_trace_vprintk
without manual conversion of varargs to u64 array. Previous
implementation of bpf_printk macro is moved to __bpf_printk for use by
the new implementation.
This does change behavior of bpf_printk calls with >3 args in the "new
libbpf, old kernels" scenario. Before this patch, attempting to use 4
args to bpf_printk results in a compile-time error. After this patch,
using bpf_printk with 4 args results in a trace_vprintk helper call
being emitted and a load-time failure on older kernels.
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
---
tools/lib/bpf/bpf_helpers.h | 45 ++++++++++++++++++++++++++++++-------
1 file changed, 37 insertions(+), 8 deletions(-)
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index b9987c3efa3c..a7e73be6dac4 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -14,14 +14,6 @@
#define __type(name, val) typeof(val) *name
#define __array(name, val) typeof(val) *name[]
-/* Helper macro to print out debug messages */
-#define bpf_printk(fmt, ...) \
-({ \
- char ____fmt[] = fmt; \
- bpf_trace_printk(____fmt, sizeof(____fmt), \
- ##__VA_ARGS__); \
-})
-
/*
* Helper macro to place programs, maps, license in
* different sections in elf_bpf file. Section names
@@ -224,4 +216,41 @@ enum libbpf_tristate {
___param, sizeof(___param)); \
})
+/* Helper macro to print out debug messages */
+#define __bpf_printk(fmt, ...) \
+({ \
+ char ____fmt[] = fmt; \
+ bpf_trace_printk(____fmt, sizeof(____fmt), \
+ ##__VA_ARGS__); \
+})
+
+/*
+ * __bpf_vprintk wraps the bpf_trace_vprintk helper with variadic arguments
+ * instead of an array of u64.
+ */
+#define __bpf_vprintk(fmt, args...) \
+({ \
+ static const char ___fmt[] = fmt; \
+ unsigned long long ___param[___bpf_narg(args)]; \
+ \
+ _Pragma("GCC diagnostic push") \
+ _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
+ ___bpf_fill(___param, args); \
+ _Pragma("GCC diagnostic pop") \
+ \
+ bpf_trace_vprintk(___fmt, sizeof(___fmt), \
+ ___param, sizeof(___param)); \
+})
+
+/* Use __bpf_printk when bpf_printk call has 3 or fewer fmt args
+ * Otherwise use __bpf_vprintk
+ */
+#define ___bpf_pick_printk(...) \
+ ___bpf_nth(_, ##__VA_ARGS__, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \
+ __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \
+ __bpf_vprintk, __bpf_vprintk, __bpf_printk /*3*/, __bpf_printk /*2*/,\
+ __bpf_printk /*1*/, __bpf_printk /*0*/)
+
+#define bpf_printk(fmt, args...) ___bpf_pick_printk(args)(fmt, ##args)
+
#endif
--
2.30.2
next prev parent reply other threads:[~2021-09-02 17:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-02 17:19 [PATCH v4 bpf-next 0/9] bpf: implement variadic printk helper Dave Marchevsky
2021-09-02 17:19 ` [PATCH v4 bpf-next 1/9] bpf: merge printk and seq_printf VARARG max macros Dave Marchevsky
2021-09-02 17:19 ` [PATCH v4 bpf-next 2/9] selftests/bpf: stop using bpf_program__load Dave Marchevsky
2021-09-02 22:58 ` Andrii Nakryiko
2021-09-02 17:19 ` [PATCH v4 bpf-next 3/9] bpf: add bpf_trace_vprintk helper Dave Marchevsky
2021-09-02 17:19 ` Dave Marchevsky [this message]
2021-09-02 23:08 ` [PATCH v4 bpf-next 4/9] libbpf: Modify bpf_printk to choose helper based on arg count Andrii Nakryiko
2021-09-02 17:19 ` [PATCH v4 bpf-next 5/9] libbpf: use static const fmt string in __bpf_printk Dave Marchevsky
2021-09-02 23:09 ` Andrii Nakryiko
2021-09-02 17:19 ` [PATCH v4 bpf-next 6/9] bpftool: only probe trace_vprintk feature in 'full' mode Dave Marchevsky
2021-09-02 23:10 ` Andrii Nakryiko
2021-09-02 17:19 ` [PATCH v4 bpf-next 7/9] selftests/bpf: Migrate prog_tests/trace_printk CHECKs to ASSERTs Dave Marchevsky
2021-09-02 17:19 ` [PATCH v4 bpf-next 8/9] selftests/bpf: add trace_vprintk test prog Dave Marchevsky
2021-09-02 23:13 ` Andrii Nakryiko
2021-09-02 17:19 ` [PATCH v4 bpf-next 9/9] selftests/bpf: Add test for bpf_printk w/ 0 fmt args Dave Marchevsky
2021-09-02 23:14 ` Andrii Nakryiko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210902171929.3922667-5-davemarchevsky@fb.com \
--to=davemarchevsky@fb.com \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=netdev@vger.kernel.org \
--cc=yhs@fb.com \
--subject='Re: [PATCH v4 bpf-next 4/9] libbpf: Modify bpf_printk to choose helper based on arg count' \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).