[PATCH bpf-next V2] bpf: avoid uninitialized value in BPF_CORE_READ_BITFIELD

[PATCH bpf-next V2] bpf: avoid uninitialized value in BPF_CORE_READ_BITFIELD

[Jose E. Marchesi]

[Changes from V1:
 - Use a default branch in the switch statement to initialize `val'.]

GCC warns that `val' may be used uninitialized in the
BPF_CRE_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 adds a default entry in the switch statement that sets
`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@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
---
 tools/lib/bpf/bpf_core_read.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
index b5c7ce5c243a..c0e13cdf9660 100644
--- a/tools/lib/bpf/bpf_core_read.h
+++ b/tools/lib/bpf/bpf_core_read.h
@@ -104,6 +104,7 @@ enum bpf_enum_value_kind {
 	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;		      \
+	default: val = 0; break;					      \
 	}								      \
 	val <<= __CORE_RELO(s, field, LSHIFT_U64);			      \
 	if (__CORE_RELO(s, field, SIGNED))				      \
-- 
2.30.2

Re: [PATCH bpf-next V2] bpf: avoid uninitialized value in BPF_CORE_READ_BITFIELD

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Wed,  8 May 2024 12:13:13 +0200 you wrote:
> [Changes from V1:
>  - Use a default branch in the switch statement to initialize `val'.]
> 
> GCC warns that `val' may be used uninitialized in the
> BPF_CRE_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;								      \
> 	}								      \
> 
> [...]

Here is the summary with links:
  - [bpf-next,V2] bpf: avoid uninitialized value in BPF_CORE_READ_BITFIELD
    https://git.kernel.org/bpf/bpf-next/c/009367099eb6

You are awesome, thank you!
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