On Wed, May 18, 2022 at 5:30 AM Eugene Syromiatnikov <esyr@xxxxxxxxxx> wrote: > > On Wed, May 18, 2022 at 01:24:56PM +0200, Jiri Olsa wrote: > > On Tue, May 17, 2022 at 02:34:55PM -0700, Yonghong Song wrote: > > > On 5/17/22 1:03 PM, Jiri Olsa wrote: > > > > On Tue, May 17, 2022 at 02:30:50PM +0200, Eugene Syromiatnikov wrote: > > > > > On Tue, May 17, 2022 at 11:12:34AM +0200, Jiri Olsa wrote: > > > > > > On Tue, May 17, 2022 at 09:36:47AM +0200, Eugene Syromiatnikov wrote: > > > > > > > With the interface as defined, it is impossible to pass 64-bit kernel > > > > > > > addresses from a 32-bit userspace process in BPF_LINK_TYPE_KPROBE_MULTI, > > > > > > > which severly limits the useability of the interface, change the ABI > > > > > > > to accept an array of u64 values instead of (kernel? user?) longs. > > > > > > > Interestingly, the rest of the libbpf infrastructure uses 64-bit values > > > > > > > for kallsyms addresses already, so this patch also eliminates > > > > > > > the sym_addr cast in tools/lib/bpf/libbpf.c:resolve_kprobe_multi_cb(). > > > > > > > > > > > > so the problem is when we have 32bit user sace on 64bit kernel right? > > > > > > > > > > > > I think we should keep addrs as longs in uapi and have kernel to figure out > > > > > > if it needs to read u32 or u64, like you did for symbols in previous patch > > > > > > > > > > No, it's not possible here, as addrs are kernel addrs and not user space > > > > > addrs, so user space has to explicitly pass 64-bit addresses on 64-bit > > > > > kernels (or have a notion whether it is running on a 64-bit > > > > > or 32-bit kernel, and form the passed array accordingly, which is against > > > > > the idea of compat layer that tries to abstract it out). > > > > > > > > hum :-\ I'll need to check on compat layer.. there must > > > > be some other code doing this already somewhere, right? > > > > so the 32bit application running on 64bit kernel using libbpf won't > > work at the moment, right? because it sees: > > > > bpf_kprobe_multi_opts::addrs as its 'unsigned long' > > > > which is 4 bytes and it needs to put there 64bits kernel addresses > > > > if we force the libbpf interface to use u64, then we should be fine > > Yes, that's correct. > > > > I am not familiar with all these compatibility thing. But if we > > > have 64-bit pointer for **syms, maybe we could also have > > > 64-bit pointer for *syms for consistency? > > > > right, perhaps we could have one function to read both syms and addrs arrays > > The distinction here it that syms are user space pointers (so they are > naturally 32-bit for 32-bit applications) and addrs are kernel-space > pointers (so they may be 64-bit even when the application is 32-bit). > Nothing prevents from changing the interface so that syms is an array > of 64-bit values treated as user space pointers, of course. I agree. User-space pointers should stay pointers in libbpf API , while kernel addresses are not really pointers for user-space app, so marking it as __u64 seems right. > > > > > > > we'll need to fix also bpf_kprobe_multi_cookie_swap because it assumes > > > > > > 64bit user space pointers > > > > if we have both addresses and cookies 64 then this should be ok > > > > > > > > > > > > > > would be gret if we could have selftest for this > > > > let's add selftest for this > > Sure, I'll try to write one. >
