* [PATCH] bpf: suppress -Wcast-function-type warning
@ 2020-10-26 21:03 Arnd Bergmann
2020-10-26 22:20 ` David Laight
2020-10-26 22:26 ` Andrii Nakryiko
0 siblings, 2 replies; 3+ messages in thread
From: Arnd Bergmann @ 2020-10-26 21:03 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann
Cc: Arnd Bergmann, Martin KaFai Lau, Song Liu, Yonghong Song,
Andrii Nakryiko, John Fastabend, KP Singh, David Miller,
Thomas Gleixner, Jakub Sitnicki, Björn Töpel,
Toke Høiland-Jørgensen, Jiri Olsa, Pankaj Bharadiya,
netdev, bpf, linux-kernel
From: Arnd Bergmann <arnd@arndb.de>
Building with -Wextra shows lots of warnings in the bpf
code such as
kernel/bpf/verifier.c: In function ‘jit_subprogs’:
include/linux/filter.h:345:4: warning: cast between incompatible function types from ‘unsigned int (*)(const void *, const struct bpf_insn *)’ to ‘u64 (*)(u64, u64, u64, u64, u64)’ {aka ‘long long unsigned int (*)(long long unsigned int, long long unsigned int, long long unsigned int, long long unsigned int, long long unsigned int)’} [-Wcast-function-type]
345 | ((u64 (*)(u64, u64, u64, u64, u64))(x))
| ^
kernel/bpf/verifier.c:10706:16: note: in expansion of macro ‘BPF_CAST_CALL’
10706 | insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) -
| ^~~~~~~~~~~~~
This appears to be intentional, so change the cast in a way that
suppresses the warning.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
include/linux/filter.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 1b62397bd124..20ba04583eaa 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -342,7 +342,7 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
/* Function call */
#define BPF_CAST_CALL(x) \
- ((u64 (*)(u64, u64, u64, u64, u64))(x))
+ ((u64 (*)(u64, u64, u64, u64, u64))(uintptr_t)(x))
#define BPF_EMIT_CALL(FUNC) \
((struct bpf_insn) { \
--
2.27.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* RE: [PATCH] bpf: suppress -Wcast-function-type warning
2020-10-26 21:03 [PATCH] bpf: suppress -Wcast-function-type warning Arnd Bergmann
@ 2020-10-26 22:20 ` David Laight
2020-10-26 22:26 ` Andrii Nakryiko
1 sibling, 0 replies; 3+ messages in thread
From: David Laight @ 2020-10-26 22:20 UTC (permalink / raw)
To: 'Arnd Bergmann', Alexei Starovoitov, Daniel Borkmann
Cc: Arnd Bergmann, Martin KaFai Lau, Song Liu, Yonghong Song,
Andrii Nakryiko, John Fastabend, KP Singh, David Miller,
Thomas Gleixner, Jakub Sitnicki, Björn Töpel,
Toke Høiland-Jørgensen, Jiri Olsa, Pankaj Bharadiya,
netdev, bpf, linux-kernel
From: Arnd Bergmann
> Sent: 26 October 2020 21:03
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> Building with -Wextra shows lots of warnings in the bpf
> code such as
>
> kernel/bpf/verifier.c: In function ‘jit_subprogs’:
> include/linux/filter.h:345:4: warning: cast between incompatible function types from ‘unsigned int
> (*)(const void *, const struct bpf_insn *)’ to ‘u64 (*)(u64, u64, u64, u64, u64)’ {aka ‘long long
> unsigned int (*)(long long unsigned int, long long unsigned int, long long unsigned int, long long
> unsigned int, long long unsigned int)’} [-Wcast-function-type]
> 345 | ((u64 (*)(u64, u64, u64, u64, u64))(x))
> | ^
> kernel/bpf/verifier.c:10706:16: note: in expansion of macro ‘BPF_CAST_CALL’
> 10706 | insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) -
> | ^~~~~~~~~~~~~
>
> This appears to be intentional, so change the cast in a way that
> suppresses the warning.
It is also utterly horrid.
If the value is ever cast back then there is a lot of scope
for it going badly wrong somewhere.
It certainly isn't valid to use the target type to call the original function.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] bpf: suppress -Wcast-function-type warning
2020-10-26 21:03 [PATCH] bpf: suppress -Wcast-function-type warning Arnd Bergmann
2020-10-26 22:20 ` David Laight
@ 2020-10-26 22:26 ` Andrii Nakryiko
1 sibling, 0 replies; 3+ messages in thread
From: Andrii Nakryiko @ 2020-10-26 22:26 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Alexei Starovoitov, Daniel Borkmann, Arnd Bergmann,
Martin KaFai Lau, Song Liu, Yonghong Song, Andrii Nakryiko,
John Fastabend, KP Singh, David Miller, Thomas Gleixner,
Jakub Sitnicki, Björn Töpel,
Toke Høiland-Jørgensen, Jiri Olsa, Pankaj Bharadiya,
Networking, bpf, open list
On Mon, Oct 26, 2020 at 2:03 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> Building with -Wextra shows lots of warnings in the bpf
> code such as
>
> kernel/bpf/verifier.c: In function ‘jit_subprogs’:
> include/linux/filter.h:345:4: warning: cast between incompatible function types from ‘unsigned int (*)(const void *, const struct bpf_insn *)’ to ‘u64 (*)(u64, u64, u64, u64, u64)’ {aka ‘long long unsigned int (*)(long long unsigned int, long long unsigned int, long long unsigned int, long long unsigned int, long long unsigned int)’} [-Wcast-function-type]
> 345 | ((u64 (*)(u64, u64, u64, u64, u64))(x))
> | ^
> kernel/bpf/verifier.c:10706:16: note: in expansion of macro ‘BPF_CAST_CALL’
> 10706 | insn->imm = BPF_CAST_CALL(func[subprog]->bpf_func) -
> | ^~~~~~~~~~~~~
>
> This appears to be intentional, so change the cast in a way that
> suppresses the warning.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
LGTM.
Acked-by: Andrii Nakryiko <andrii@kernel.org>
> include/linux/filter.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 1b62397bd124..20ba04583eaa 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -342,7 +342,7 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
> /* Function call */
>
> #define BPF_CAST_CALL(x) \
> - ((u64 (*)(u64, u64, u64, u64, u64))(x))
> + ((u64 (*)(u64, u64, u64, u64, u64))(uintptr_t)(x))
>
> #define BPF_EMIT_CALL(FUNC) \
> ((struct bpf_insn) { \
> --
> 2.27.0
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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