2019-05-20 21:51:23

by Matteo Croce

Subject: [PATCH bpf] samples/bpf: suppress compiler warning

GCC 9 fails to calculate the size of local constant strings and produces a
false positive:

samples/bpf/task_fd_query_user.c: In function ‘test_debug_fs_uprobe’:
samples/bpf/task_fd_query_user.c:242:67: warning: ‘%s’ directive output may be truncated writing up to 255 bytes into a region of size 215 [-Wformat-truncation=]
242 | snprintf(buf, sizeof(buf), "/sys/kernel/debug/tracing/events/%ss/%s/id",
| ^~
243 | event_type, event_alias);
| ~~~~~~~~~~~
samples/bpf/task_fd_query_user.c:242:2: note: ‘snprintf’ output between 45 and 300 bytes into a destination of size 256
242 | snprintf(buf, sizeof(buf), "/sys/kernel/debug/tracing/events/%ss/%s/id",
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
243 | event_type, event_alias);
| ~~~~~~~~~~~~~~~~~~~~~~~~

Workaround this by lowering the buffer size to a reasonable value.
Related GCC Bugzilla: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83431

Signed-off-by: Matteo Croce <[email protected]>
---
samples/bpf/task_fd_query_user.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/bpf/task_fd_query_user.c b/samples/bpf/task_fd_query_user.c
index aff2b4ae914e..e39938058223 100644
--- a/samples/bpf/task_fd_query_user.c
+++ b/samples/bpf/task_fd_query_user.c
@@ -216,7 +216,7 @@ static int test_debug_fs_uprobe(char *binary_path, long offset, bool is_return)
{
const char *event_type = "uprobe";
struct perf_event_attr attr = {};
- char buf[256], event_alias[256];
+ char buf[256], event_alias[sizeof("test_1234567890")];
__u64 probe_offset, probe_addr;
__u32 len, prog_id, fd_type;
int err, res, kfd, efd;
--
2.21.0

2019-05-21 14:58:00

by Daniel Borkmann

Subject: Re: [PATCH bpf] samples/bpf: suppress compiler warning

On 05/20/2019 11:49 PM, Matteo Croce wrote:
> GCC 9 fails to calculate the size of local constant strings and produces a
> false positive:
>
> samples/bpf/task_fd_query_user.c: In function ‘test_debug_fs_uprobe’:
> samples/bpf/task_fd_query_user.c:242:67: warning: ‘%s’ directive output may be truncated writing up to 255 bytes into a region of size 215 [-Wformat-truncation=]
> 242 | snprintf(buf, sizeof(buf), "/sys/kernel/debug/tracing/events/%ss/%s/id",
> | ^~
> 243 | event_type, event_alias);
> | ~~~~~~~~~~~
> samples/bpf/task_fd_query_user.c:242:2: note: ‘snprintf’ output between 45 and 300 bytes into a destination of size 256
> 242 | snprintf(buf, sizeof(buf), "/sys/kernel/debug/tracing/events/%ss/%s/id",
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 243 | event_type, event_alias);
> | ~~~~~~~~~~~~~~~~~~~~~~~~
>
> Workaround this by lowering the buffer size to a reasonable value.
> Related GCC Bugzilla: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83431
>
> Signed-off-by: Matteo Croce <[email protected]>

Applied, thanks!