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Date: Thu, 17 Dec 2020 10:54:34 +0100 From: Christophe Leroy <christophe.leroy@...roup.eu> To: Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Michael Ellerman <mpe@...erman.id.au>, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com, john.fastabend@...il.com, kpsingh@...omium.org, naveen.n.rao@...ux.ibm.com, sandipan@...ux.ibm.com, linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org, bpf@...r.kernel.org Subject: Re: [RFC PATCH v1 7/7] powerpc/bpf: Implement extended BPF on PPC32 Le 17/12/2020 à 07:11, Alexei Starovoitov a écrit : > On Wed, Dec 16, 2020 at 10:07:37AM +0000, Christophe Leroy wrote: >> Implement Extended Berkeley Packet Filter on Powerpc 32 >> >> Test result with test_bpf module: >> >> test_bpf: Summary: 378 PASSED, 0 FAILED, [354/366 JIT'ed] > > nice! > >> Registers mapping: >> >> [BPF_REG_0] = r11-r12 >> /* function arguments */ >> [BPF_REG_1] = r3-r4 >> [BPF_REG_2] = r5-r6 >> [BPF_REG_3] = r7-r8 >> [BPF_REG_4] = r9-r10 >> [BPF_REG_5] = r21-r22 (Args 9 and 10 come in via the stack) >> /* non volatile registers */ >> [BPF_REG_6] = r23-r24 >> [BPF_REG_7] = r25-r26 >> [BPF_REG_8] = r27-r28 >> [BPF_REG_9] = r29-r30 >> /* frame pointer aka BPF_REG_10 */ >> [BPF_REG_FP] = r31 >> /* eBPF jit internal registers */ >> [BPF_REG_AX] = r19-r20 >> [TMP_REG] = r18 >> >> As PPC32 doesn't have a redzone in the stack, >> use r17 as tail call counter. >> >> r0 is used as temporary register as much as possible. It is referenced >> directly in the code in order to avoid misuse of it, because some >> instructions interpret it as value 0 instead of register r0 >> (ex: addi, addis, stw, lwz, ...) >> >> The following operations are not implemented: >> >> case BPF_ALU64 | BPF_DIV | BPF_X: /* dst /= src */ >> case BPF_ALU64 | BPF_MOD | BPF_X: /* dst %= src */ >> case BPF_STX | BPF_XADD | BPF_DW: /* *(u64 *)(dst + off) += src */ >> >> The following operations are only implemented for power of two constants: >> >> case BPF_ALU64 | BPF_MOD | BPF_K: /* dst %= imm */ >> case BPF_ALU64 | BPF_DIV | BPF_K: /* dst /= imm */ > > Those are sensible limitations. MOD and DIV are rare, but XADD is common. > Please consider doing it as a cmpxchg loop in the future. > > Also please run test_progs. It will give a lot better coverage than test_bpf.ko > I'm having hard time cross building test_progs: ~/linux-powerpc/tools/testing/selftests/bpf/$ make CROSS_COMPILE=ppc-linux- ... GEN /home/chr/linux-powerpc/tools/testing/selftests/bpf/tools/build/bpftool/Documentation/bpf-helpers.7 INSTALL eBPF_helpers-manpage INSTALL Documentation-man GEN vmlinux.h /bin/sh: /home/chr/linux-powerpc/tools/testing/selftests/bpf/tools/sbin/bpftool: cannot execute binary file make: *** [/home/chr/linux-powerpc/tools/testing/selftests/bpf/tools/include/vmlinux.h] Error 126 make: *** Deleting file `/home/chr/linux-powerpc/tools/testing/selftests/bpf/tools/include/vmlinux.h' Looks like it builds bpftool for powerpc and tries to run it on my x86. How should I proceed ? Thanks Christophe
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