[bpf-next,v1] bpftool: Silence build warning about calloc()

Commit Message

Tiezhu Yang Jan. 16, 2024, 6:19 a.m. UTC

There exists the following warning when building bpftool:

  CC      prog.o
prog.c: In function ‘profile_open_perf_events’:
prog.c:2301:24: warning: ‘calloc’ sizes specified with ‘sizeof’ in the earlier argument and not in the later argument [-Wcalloc-transposed-args]
 2301 |                 sizeof(int), obj->rodata->num_cpu * obj->rodata->num_metric);
      |                        ^~~
prog.c:2301:24: note: earlier argument should specify number of elements, later size of each element

Tested with the latest upstream GCC which contains a new warning option
-Wcalloc-transposed-args. The first argument to calloc is documented to
be number of elements in array, while the second argument is size of each
element, just switch the first and second arguments of calloc() to silence
the build warning, compile tested only.

Fixes: 47c09d6a9f67 ("bpftool: Introduce "prog profile" command")
Signed-off-by: Tiezhu Yang <[e-mail]>
---
 tools/bpf/bpftool/prog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Quentin Monnet Jan. 16, 2024, 11:15 a.m. UTC | #1

2024-01-16 06:19 UTC+0000 ~ Tiezhu Yang <[e-mail]>
> There exists the following warning when building bpftool:
> 
>   CC      prog.o
> prog.c: In function ‘profile_open_perf_events’:
> prog.c:2301:24: warning: ‘calloc’ sizes specified with ‘sizeof’ in the earlier argument and not in the later argument [-Wcalloc-transposed-args]
>  2301 |                 sizeof(int), obj->rodata->num_cpu * obj->rodata->num_metric);
>       |                        ^~~
> prog.c:2301:24: note: earlier argument should specify number of elements, later size of each element
> 
> Tested with the latest upstream GCC which contains a new warning option
> -Wcalloc-transposed-args. The first argument to calloc is documented to
> be number of elements in array, while the second argument is size of each
> element, just switch the first and second arguments of calloc() to silence
> the build warning, compile tested only.
> 
> Fixes: 47c09d6a9f67 ("bpftool: Introduce "prog profile" command")
> Signed-off-by: Tiezhu Yang <[e-mail]>

Reviewed-by: Quentin Monnet <[e-mail]>

Thank you!

[e-mail] Jan. 16, 2024, 3:30 p.m. UTC | #2

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <[e-mail]>:

On Tue, 16 Jan 2024 14:19:20 +0800 you wrote:
> There exists the following warning when building bpftool:
> 
>   CC      prog.o
> prog.c: In function ‘profile_open_perf_events’:
> prog.c:2301:24: warning: ‘calloc’ sizes specified with ‘sizeof’ in the earlier argument and not in the later argument [-Wcalloc-transposed-args]
>  2301 |                 sizeof(int), obj->rodata->num_cpu * obj->rodata->num_metric);
>       |                        ^~~
> prog.c:2301:24: note: earlier argument should specify number of elements, later size of each element
> 
> [...]

Here is the summary with links:
  - [bpf-next,v1] bpftool: Silence build warning about calloc()
    https://git.kernel.org/bpf/bpf-next/c/d2729bb2c7e1

You are awesome, thank you!

Patch

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index feb8e305804f..9cb42a3366c0 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -2298,7 +2298,7 @@  static int profile_open_perf_events(struct profiler_bpf *obj)
 	int map_fd;
 
 	profile_perf_events = calloc(
-		sizeof(int), obj->rodata->num_cpu * obj->rodata->num_metric);
+		obj->rodata->num_cpu * obj->rodata->num_metric, sizeof(int));
 	if (!profile_perf_events) {
 		p_err("failed to allocate memory for perf_event array: %s",
 		      strerror(errno));