Le 06/01/2023 à 16:37, Daniel Borkmann a écrit : > On 1/5/23 6:53 PM, Christophe Leroy wrote: >> Le 05/01/2023 à 04:06, tong@xxxxxxxxxxxxx a écrit : >>> From: Tonghao Zhang <tong@xxxxxxxxxxxxx> >>> >>> The x86_64 can't dump the valid insn in this way. A test BPF prog >>> which include subprog: >>> >>> $ llvm-objdump -d subprog.o >>> Disassembly of section .text: >>> 0000000000000000 <subprog>: >>> 0: 18 01 00 00 73 75 62 70 00 00 00 00 72 6f 67 00 r1 >>> = 29114459903653235 ll >>> 2: 7b 1a f8 ff 00 00 00 00 *(u64 *)(r10 - 8) = r1 >>> 3: bf a1 00 00 00 00 00 00 r1 = r10 >>> 4: 07 01 00 00 f8 ff ff ff r1 += -8 >>> 5: b7 02 00 00 08 00 00 00 r2 = 8 >>> 6: 85 00 00 00 06 00 00 00 call 6 >>> 7: 95 00 00 00 00 00 00 00 exit >>> Disassembly of section raw_tp/sys_enter: >>> 0000000000000000 <entry>: >>> 0: 85 10 00 00 ff ff ff ff call -1 >>> 1: b7 00 00 00 00 00 00 00 r0 = 0 >>> 2: 95 00 00 00 00 00 00 00 exit >>> >>> kernel print message: >>> [ 580.775387] flen=8 proglen=51 pass=3 image=ffffffffa000c20c >>> from=kprobe-load pid=1643 >>> [ 580.777236] JIT code: 00000000: cc cc cc cc cc cc cc cc cc cc cc >>> cc cc cc cc cc >>> [ 580.779037] JIT code: 00000010: cc cc cc cc cc cc cc cc cc cc cc >>> cc cc cc cc cc >>> [ 580.780767] JIT code: 00000020: cc cc cc cc cc cc cc cc cc cc cc >>> cc cc cc cc cc >>> [ 580.782568] JIT code: 00000030: cc cc cc >>> >>> $ bpf_jit_disasm >>> 51 bytes emitted from JIT compiler (pass:3, flen:8) >>> ffffffffa000c20c + <x>: >>> 0: int3 >>> 1: int3 >>> 2: int3 >>> 3: int3 >>> 4: int3 >>> 5: int3 >>> ... >>> >>> Until bpf_jit_binary_pack_finalize is invoked, we copy rw_header to >>> header >>> and then image/insn is valid. BTW, we can use the "bpftool prog dump" >>> JITed instructions. >> >> NACK. >> >> Because the feature is buggy on x86_64, you remove it for all >> architectures ? >> >> On powerpc bpf_jit_enable == 2 works and is very usefull. >> >> Last time I tried to use bpftool on powerpc/32 it didn't work. I don't >> remember the details, I think it was an issue with endianess. Maybe it >> is fixed now, but it needs to be verified. >> >> So please, before removing a working and usefull feature, make sure >> there is an alternative available to it for all architectures in all >> configurations. >> >> Also, I don't think bpftool is usable to dump kernel BPF selftests. >> That's vital when a selftest fails if you want to have a chance to >> understand why it fails. > > If this is actively used by JIT developers and considered useful, I'd be > ok to leave it for the time being. Overall goal is to reach feature parity > among (at least major arch) JITs and not just have most functionality only > available on x86-64 JIT. Could you however check what is not working with > bpftool on powerpc/32? Perhaps it's not too much effort to just fix it, > but details would be useful otherwise 'it didn't work' is too fuzzy. Sure I will try to test bpftool again in the coming days. Previous discussion about that subject is here: https://patchwork.kernel.org/project/linux-riscv/patch/20210415093250.3391257-1-Jianlin.Lv@xxxxxxx/#24176847 > > Also, with regards to the last statement that bpftool is not usable to > dump kernel BPF selftests. Could you elaborate some more? I haven't used > bpf_jit_enable == 2 in a long time and for debugging always relied on > bpftool to dump xlated insns or JIT. Or do you mean by BPF selftests > the test_bpf.ko module? Given it has a big batch with kernel-only tests, > there I can see it's probably still useful. Yes I mean test_bpf.ko I used it as the test basis when I implemented eBPF for powerpc/32. And not so long ago it helped decover and fix a bug, see https://github.com/torvalds/linux/commit/89d21e259a94f7d5582ec675aa445f5a79f347e4 > > Cheers, > Daniel
