| Message ID | 20201026210332.3885166-1-arnd@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf: suppress -Wcast-function-type warning | expand |
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)
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 >
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) { \