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>
Subject: Re: [PATCH v3 bpf-next 3/7] libbpf: Modify bpf_printk to choose helper based on arg count
Date: Sat, 28 Aug 2021 12:44:48 -0400 [thread overview]
Message-ID: <9e742d39-1ee0-b08b-9ee9-edf5b8687d8d@fb.com> (raw)
In-Reply-To: <20210828052006.1313788-4-davemarchevsky@fb.com>
On 8/28/21 1:20 AM, Dave Marchevsky wrote:
> 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..5f087306cdfe 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)); \
> +})
> +
> +#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, __bpf_printk, \
> + __bpf_printk, __bpf_printk)
> +
> +#define bpf_printk(fmt, args...) \
> +({ \
> + ___bpf_pick_printk(args)(fmt, args); \
While looking at test failure related to patch 4, noticed
that this isn't handling 0 format arg case correctly, resulting
in compilation error.
Need to fix and add a test as all extant selftests are doing
bpf_printk with at least 1 format arg.
> +})
> +
> #endif
>
next prev parent reply other threads:[~2021-08-28 17:25 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-28 5:19 [PATCH v3 bpf-next 0/7] bpf: implement variadic printk helper Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 1/7] bpf: merge printk and seq_printf VARARG max macros Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 2/7] bpf: add bpf_trace_vprintk helper Dave Marchevsky
2021-08-30 23:35 ` Andrii Nakryiko
2021-09-03 8:00 ` Daniel Borkmann
2021-09-13 17:30 ` Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 3/7] libbpf: Modify bpf_printk to choose helper based on arg count Dave Marchevsky
2021-08-28 16:44 ` Dave Marchevsky [this message]
2021-08-28 5:20 ` [PATCH v3 bpf-next 4/7] libbpf: use static const fmt string in __bpf_printk Dave Marchevsky
2021-08-28 16:40 ` Dave Marchevsky
2021-08-29 16:57 ` Alexei Starovoitov
2021-08-31 0:36 ` Andrii Nakryiko
2021-08-31 0:37 ` Andrii Nakryiko
2021-08-28 5:20 ` [PATCH v3 bpf-next 5/7] bpftool: only probe trace_vprintk feature in 'full' mode Dave Marchevsky
2021-08-28 5:20 ` [PATCH v3 bpf-next 6/7] selftests/bpf: Migrate prog_tests/trace_printk CHECKs to ASSERTs Dave Marchevsky
2021-08-31 0:03 ` Andrii Nakryiko
2021-08-28 5:20 ` [PATCH v3 bpf-next 7/7] selftests/bpf: add trace_vprintk test prog Dave Marchevsky
2021-08-31 0:04 ` 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=9e742d39-1ee0-b08b-9ee9-edf5b8687d8d@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 \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).