2021-12-25 08:32:54

by Qiang Wang

Subject: [PATCH 1/2] libbpf: Use probe_name for legacy kprobe

Fix a bug in commit 46ed5fc33db9, which wrongly used the
func_name instead of probe_name to register legacy kprobe.

Fixes: 46ed5fc33db9 ("libbpf: Refactor and simplify legacy kprobe code")
Co-developed-by: Chengming Zhou <[email protected]>
Signed-off-by: Qiang Wang <[email protected]>
Signed-off-by: Chengming Zhou <[email protected]>
---
tools/lib/bpf/libbpf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7c74342bb668..b7d6c951fa09 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9735,7 +9735,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name),
func_name, offset);

- legacy_probe = strdup(func_name);
+ legacy_probe = strdup(probe_name);
if (!legacy_probe)
return libbpf_err_ptr(-ENOMEM);

--
2.20.1

2021-12-25 08:33:05

by Qiang Wang

Subject: [PATCH 2/2] libbpf: Support repeated legacy kprobes on same function

If repeated legacy kprobes on same function in one process,
libbpf will register using the same probe name and got -EBUSY
error. So append index to the probe name format to fix this
problem.

Co-developed-by: Chengming Zhou <[email protected]>
Signed-off-by: Qiang Wang <[email protected]>
Signed-off-by: Chengming Zhou <[email protected]>
---
tools/lib/bpf/libbpf.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b7d6c951fa09..0c41a45ffd54 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9634,7 +9634,9 @@ static int append_to_file(const char *file, const char *fmt, ...)
static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
const char *kfunc_name, size_t offset)
{
- snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), kfunc_name, offset);
+ static int index = 0;
+ snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx_%d", getpid(), kfunc_name, offset
+ __sync_fetch_and_add(&index, 1));
}

static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,
--
2.20.1

2021-12-27 11:40:01

by Hengqi Chen

Subject: Re: [PATCH 2/2] libbpf: Support repeated legacy kprobes on same function

On 2021/12/25 4:32 PM, Qiang Wang wrote:
> If repeated legacy kprobes on same function in one process,
> libbpf will register using the same probe name and got -EBUSY
> error. So append index to the probe name format to fix this
> problem.
>
> Co-developed-by: Chengming Zhou <[email protected]>
> Signed-off-by: Qiang Wang <[email protected]>
> Signed-off-by: Chengming Zhou <[email protected]>
> ---
> tools/lib/bpf/libbpf.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b7d6c951fa09..0c41a45ffd54 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9634,7 +9634,9 @@ static int append_to_file(const char *file, const char *fmt, ...)
> static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
> const char *kfunc_name, size_t offset)
> {
> - snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), kfunc_name, offset);
> + static int index = 0;

Add empty line after variable declaration.

> + snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx_%d", getpid(), kfunc_name, offset

Missing a comma after offset.

> + __sync_fetch_and_add(&index, 1));
> }
>
> static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,

2021-12-27 11:47:40

by Hengqi Chen

Subject: Re: [PATCH 1/2] libbpf: Use probe_name for legacy kprobe

On 2021/12/25 4:32 PM, Qiang Wang wrote:
> Fix a bug in commit 46ed5fc33db9, which wrongly used the
> func_name instead of probe_name to register legacy kprobe.
>
> Fixes: 46ed5fc33db9 ("libbpf: Refactor and simplify legacy kprobe code")
> Co-developed-by: Chengming Zhou <[email protected]>
> Signed-off-by: Qiang Wang <[email protected]>
> Signed-off-by: Chengming Zhou <[email protected]>
> ---
> tools/lib/bpf/libbpf.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 7c74342bb668..b7d6c951fa09 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9735,7 +9735,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
> gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name),
> func_name, offset);
>
> - legacy_probe = strdup(func_name);
> + legacy_probe = strdup(probe_name);
> if (!legacy_probe)
> return libbpf_err_ptr(-ENOMEM);
>

Reviewed-by: Hengqi Chen <[email protected]>
Tested-by: Hengqi Chen <[email protected]>