On Tue, Apr 16, 2019 at 7:34 AM Ananyev, Konstantin <konstantin.ananyev@xxxxxxxxx> wrote: > > > > > -----Original Message----- > > From: Alexei Starovoitov [mailto:alexei.starovoitov@xxxxxxxxx] > > Sent: Tuesday, April 16, 2019 2:01 AM > > To: Ananyev, Konstantin <konstantin.ananyev@xxxxxxxxx>; bpf <bpf@xxxxxxxxxxxxxxx> > > Subject: Re: FW: BPF_PSEUDO_CALL question > > > > On Mon, Apr 15, 2019 at 5:13 AM Ananyev, Konstantin > > <konstantin.ananyev@xxxxxxxxx> wrote: > > > > > > Hi Alexei, > > > I posted the question below on llvm-dev mailing list, but there is no answer so far. > > > As you seems the author of BPF_PSEUDO_CALL in LLVM (and linux kernel) thought might > > > be you know the answer? > > > I looked through the patches, but didn't spot anything myself. > > > Thanks > > > Konstantin > > > > > > -----Original Message----- > > > From: llvm-dev [mailto:llvm-dev-bounces@xxxxxxxxxxxxxx] On Behalf Of Ananyev, Konstantin via llvm-dev > > > Sent: Wednesday, April 10, 2019 7:37 PM > > > To: llvm-dev@xxxxxxxxxxxxxx > > > Subject: [llvm-dev] BPF_PSEUDO_CALL question > > > > > > > > > Hi everyone, > > > with clang 6.0 and onwards, for the following code: > > > $ cat t6.c > > > > > > #include <stdint.h> > > > > > > extern int ffx1(const void *p); > > > > > > uint64_t entry(const void *p) > > > { > > > return ffx1(p); > > > } > > > > > > clang -O2 -target bpfel -c t6.c > > > generates for the call BPF_PSEUDO_CALL instruction: > > > entry: > > > 0: 85 10 00 00 ff ff ff ff call -1 > > > 1: 67 00 00 00 20 00 00 00 r0 <<= 32 > > > 2: c7 00 00 00 20 00 00 00 r0 s>>= 32 > > > 3: 95 00 00 00 00 00 00 00 exit > > > > > > Is there any way to force clang to generate proper BPF_CALL instruction, > > > i.e: 85 00 00 00 ff ff ff ff (as it did in older versions)? > > > > older version of llvm generated broken code. > > there are only two call flavors: > > - call imm -> calling particular kernel helper where imm==helper_id > > Ok but in the example above, is it possible tell to the llvm that > ffx1() is actually a kernel helper with id==X? here is how it works for helpers: static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *) BPF_FUNC_map_lookup_elem; User space can hack similar thing for any integer and any name.
