On Tue, May 7, 2024 at 4:40 AM Jose E. Marchesi
<jose.marchesi@xxxxxxxxxx> wrote:
>
> GCC warns that `val' may be used uninitialized in the
> BPF_CORE_READ_BITFIELD macro, defined in bpf_core_read.h as:
>
> [...]
> unsigned long long val; \
> [...] \
> switch (__CORE_RELO(s, field, BYTE_SIZE)) { \
> case 1: val = *(const unsigned char *)p; break; \
> case 2: val = *(const unsigned short *)p; break; \
> case 4: val = *(const unsigned int *)p; break; \
> case 8: val = *(const unsigned long long *)p; break; \
> } \
> [...]
> val; \
> } \
>
> This patch initializes `val' to zero in order to avoid the warning,
> and random values to be used in case __builtin_preserve_field_info
> returns unexpected values for BPF_FIELD_BYTE_SIZE.
>
> Tested in bpf-next master.
> No regressions.
>
> Signed-off-by: Jose E. Marchesi <jose.marchesi@xxxxxxxxxx>
> Cc: david.faust@xxxxxxxxxx
> Cc: cupertino.miranda@xxxxxxxxxx
> Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Cc: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
> tools/lib/bpf/bpf_core_read.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
> index b5c7ce5c243a..88d129b5f0a1 100644
> --- a/tools/lib/bpf/bpf_core_read.h
> +++ b/tools/lib/bpf/bpf_core_read.h
> @@ -89,7 +89,7 @@ enum bpf_enum_value_kind {
> */
> #define BPF_CORE_READ_BITFIELD(s, field) ({ \
> const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
> - unsigned long long val; \
> + unsigned long long val = 0; \
let's add instead `default: val = 0; break;`
as Yonghong mentioned, it's not expected to have invalid byte size
value in the relocation
pw-bot: cr
> \
> /* This is a so-called barrier_var() operation that makes specified \
> * variable "a black box" for optimizing compiler. \
> --
> 2.30.2
>
>
