[PATCH v4] libbpf: Fix for the potential undefined behavior due to shifting

[PATCH v4] libbpf: Fix for the potential undefined behavior due to shifting

[Tw]

When compiling libbpf with sanitation, ubsan will report the following:
```
left shift of 1 by 31 places cannot be represented in type 'int'
```
This may lead to undefined behavior according to the compiler implementation,
let's fix it by casting to unsigned counterpart before shifting.

Signed-off-by: Tan Wei <tw19881113@gmail.com>
---
v4:
 - Fix macro redefined issue in test_btf.h
 - Fix a typo in commit message
 tools/lib/bpf/libbpf.c                 | 2 +-
 tools/lib/bpf/libbpf_internal.h        | 4 ++--
 tools/testing/selftests/bpf/test_btf.h | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b749c0174..f09cbfd8e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11738,7 +11738,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
 				errstr(bit));
 			return bit;
 		}
-		attr.config |= 1 << bit;
+		attr.config |= 1ULL << bit;
 	}
 	attr.size = attr_sz;
 	attr.type = type;
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 4c46d34fc..cb4d96233 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -77,7 +77,7 @@
 #define JUMPTABLES_SEC ".jumptables"
 
 #define BTF_INFO_ENC(kind, kind_flag, vlen) \
-	((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
+	(((__u32)(!!(kind_flag)) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
 #define BTF_TYPE_ENC(name, info, size_or_type) (name), (info), (size_or_type)
 #define BTF_INT_ENC(encoding, bits_offset, nr_bits) \
 	((encoding) << 24 | (bits_offset) << 16 | (nr_bits))
@@ -259,7 +259,7 @@ static inline enum btf_func_linkage btf_func_linkage(const struct btf_type *t)
 
 static inline __u32 btf_type_info(int kind, int vlen, int kflag)
 {
-	return (kflag << 31) | (kind << 24) | vlen;
+	return ((__u32)kflag << 31) | (kind << 24) | vlen;
 }
 
 enum map_def_parts {
diff --git a/tools/testing/selftests/bpf/test_btf.h b/tools/testing/selftests/bpf/test_btf.h
index e65889ab4..e7bc78108 100644
--- a/tools/testing/selftests/bpf/test_btf.h
+++ b/tools/testing/selftests/bpf/test_btf.h
@@ -7,7 +7,7 @@
 #define BTF_END_RAW 0xdeadbeef
 
 #define BTF_INFO_ENC(kind, kind_flag, vlen)			\
-	((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
+	(((__u32)(!!(kind_flag)) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
 
 #define BTF_TYPE_ENC(name, info, size_or_type)	\
 	(name), (info), (size_or_type)
-- 
2.54.0

Re: [PATCH v4] libbpf: Fix for the potential undefined behavior due to shifting

[patchwork-bot+netdevbpf]

Hello:

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

On Fri, 28 Aug 2026 08:34:10 +0800 you wrote:
> When compiling libbpf with sanitation, ubsan will report the following:
> ```
> left shift of 1 by 31 places cannot be represented in type 'int'
> ```
> This may lead to undefined behavior according to the compiler implementation,
> let's fix it by casting to unsigned counterpart before shifting.
> 
> [...]

Here is the summary with links:
  - [v4] libbpf: Fix for the potential undefined behavior due to shifting
    https://git.kernel.org/bpf/bpf-next/c/cd35e1b10182

You are awesome, thank you!
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