powerpc/bpf: Implement extended BPF on PPC32

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]

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] = r17-r18
	/* eBPF jit internal registers */
	[BPF_REG_AX] = r19-r20
	[TMP_REG] = r31

As PPC32 doesn't have a redzone in the stack, a stack frame must always
be set in order to host at least the tail count counter.

The stack frame remains for tail calls, it is set by the first callee
and freed by the last callee.

r0 is used as temporary register as much as possible. It is referenced
directly in the code in order to avoid misusing 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 */

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/61d8b149176ddf99e7d5cef0b6dc1598583ca202.1616430991.git.christophe.leroy@csgroup.eu

Documentation/admin-guide/sysctl/net.rst

@@ -64,6 +64,7 @@ two flavors of JITs, the newer eBPF JIT currently supported on:
   - arm64
   - arm32
   - ppc64
+  - ppc32
   - sparc64
   - mips64
   - s390x
@@ -73,7 +74,6 @@ two flavors of JITs, the newer eBPF JIT currently supported on:
 And the older cBPF JIT supported on the following archs:
 
   - mips
-  - ppc
   - sparc
 
 eBPF JITs are a superset of cBPF JITs, meaning the kernel will

arch/powerpc/Kconfig

@@ -202,7 +202,7 @@ config PPC
 	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS	if MPROFILE_KERNEL
-	select HAVE_EBPF_JIT			if PPC64
+	select HAVE_EBPF_JIT
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS	if !(CPU_LITTLE_ENDIAN && POWER7_CPU)
 	select HAVE_FAST_GUP
 	select HAVE_FTRACE_MCOUNT_RECORD

arch/powerpc/net/Makefile

@@ -2,4 +2,4 @@
 #
 # Arch-specific network modules
 #
-obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o bpf_jit_comp64.o
+obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o bpf_jit_comp$(BITS).o

arch/powerpc/net/bpf_jit.h

@@ -42,6 +42,10 @@
 				EMIT(PPC_RAW_ORI(d, d, IMM_L(i)));	      \
 		} } while(0)
 
+#ifdef CONFIG_PPC32
+#define PPC_EX32(r, i)		EMIT(PPC_RAW_LI((r), (i) < 0 ? -1 : 0))
+#endif
+
 #define PPC_LI64(d, i)		do {					      \
 		if ((long)(i) >= -2147483648 &&				      \
 				(long)(i) < 2147483648)			      \