Le 17/12/2020 à 07:11, Alexei Starovoitov a écrit :

On Wed, Dec 16, 2020 at 10:07:37AM +0000, Christophe Leroy wrote:

quoted

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!

quoted

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