On Fri, Feb 4, 2022 at 8:46 AM Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx> wrote: > > Ilya Leoshkevich wrote: > > Some architectures pass a pointer to struct pt_regs to syscall > > handlers, others unpack it into individual function parameters. > > I think that is just dependent on ARCH_HAS_SYSCALL_WRAPPER, so only x86, > arm64 and s390 pass pointers to pt_regs to syscall entry points. > > > Introduce a macro to describe what a particular arch does, using > > `passing pt_regs *` as a default. > > > > Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx> > > --- > > tools/lib/bpf/bpf_tracing.h | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h > > index 30f0964f8c9e..08d2990c006f 100644 > > --- a/tools/lib/bpf/bpf_tracing.h > > +++ b/tools/lib/bpf/bpf_tracing.h > > @@ -334,6 +334,15 @@ struct pt_regs; > > > > #endif /* defined(bpf_target_defined) */ > > > > +/* > > + * When invoked from a syscall handler kprobe, returns a pointer to a > > + * struct pt_regs containing syscall arguments and suitable for passing to > > + * PT_REGS_PARMn_SYSCALL() and PT_REGS_PARMn_CORE_SYSCALL(). > > + */ > > +#ifndef PT_REGS_SYSCALL_REGS > > +#define PT_REGS_SYSCALL_REGS(ctx) ((struct pt_regs *)PT_REGS_PARM1(ctx)) > > +#endif > > + > > I think that name is misleading if an architecture doesn't implement syscall > wrappers, since you are simply getting access to the kprobe pt_regs, rather > than the syscall pt_regs. This can perhaps be named PT_REGS_SYSCALL_UNWRAP() or > such to make that clear. UNWRAP implies that there is something to unwrap, always. In case of s390x, for example, there is nothing to unwrap. So I think PT_REGS_SYSCALL_REGS() makes more sense, it just fetches correct pt_regs to work with to get syscall input arguments (and it might be exactly the same pt_regs that are passed in). I think in practice most users won't ever have to use this, as we'll add BPF_KPROBE_SYSCALL() macro, similar to BPF_KPROBE that we have now, but specific to syscall kprobe. > > Also, should this just be keyed off a simpler HAS_SYSCALL_WRAPPER or such, > rather than the other way around? I think the way Ilya did it is totally fine. > > diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h > index 032ba809f3e57a..c72f285578d3fc 100644 > --- a/tools/lib/bpf/bpf_tracing.h > +++ b/tools/lib/bpf/bpf_tracing.h > @@ -110,6 +110,8 @@ > > #endif /* __i386__ */ > > +#define HAS_SYSCALL_WRAPPER > + > #endif /* __KERNEL__ || __VMLINUX_H__ */ > > #elif defined(bpf_target_s390) > @@ -126,6 +128,7 @@ > #define __PT_RC_REG gprs[2] > #define __PT_SP_REG gprs[15] > #define __PT_IP_REG psw.addr > +#define HAS_SYSCALL_WRAPPER > > #elif defined(bpf_target_arm) > > @@ -154,6 +157,7 @@ > #define __PT_RC_REG regs[0] > #define __PT_SP_REG sp > #define __PT_IP_REG pc > +#define HAS_SYSCALL_WRAPPER > > #elif defined(bpf_target_mips) > > > We can then simply do: > > #ifdef HAS_SYSCALL_WRAPPER > #define PT_REGS_SYSCALL_UNWRAP(ctx) ((struct pt_regs *)PT_REGS_PARM1(ctx)) > #else > #define PT_REGS_SYSCALL_unwRAP(ctx) ((struct pt_regs *)(ctx)) > #endif > > > Taking this a bit further, it would be nice if we can fold in progs/bpf_misc.h > into bpf_traching.h by also including SYS_PREFIX. As far as I know, SYS_PREFIX depends not just on architecture but also on kernel version (older versions of x86-64 kernels didn't need that prefix). For selftests, given they follow the latest version of kernel it's ok to always append SYS_PREFIX, but generally speaking for user BPF apps, they would need to be more careful and check whether they need SYS_PREFIX or not. So I don't want to add SYS_PREFIX to bpf_tracing.h because it's misleading. > > > - Naveen >
