powerpc64/bpf elfv2: Setup kernel TOC in r2 on entry

In preparation for using kernel TOC, load the same in r2 on entry. With
elfv1, the kernel TOC is already setup by our caller.

We adjust the number of instructions to skip on a tail call accordingly.
We get rid of the #ifdef in bpf_jit_emit_tail_call() since
FUNCTION_DESCR_SIZE is itself under a #ifdef.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/18a05a4ceec14a8617c9dd4b7128d0afa83fd14e.1644834730.git.naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/net/bpf_jit_comp64.c

@@ -73,6 +73,9 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
 {
 	int i;
 
+	if (__is_defined(PPC64_ELF_ABI_v2))
+		PPC_BPF_LL(_R2, _R13, offsetof(struct paca_struct, kernel_toc));
+
 	/*
 	 * Initialize tail_call_cnt if we do tail calls.
 	 * Otherwise, put in NOPs so that it can be skipped when we are
@@ -87,8 +90,6 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
 		EMIT(PPC_RAW_NOP());
 	}
 
-#define BPF_TAILCALL_PROLOGUE_SIZE	8
-
 	if (bpf_has_stack_frame(ctx)) {
 		/*
 		 * We need a stack frame, but we don't necessarily need to
@@ -217,6 +218,10 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 	 */
 	int b2p_bpf_array = b2p[BPF_REG_2];
 	int b2p_index = b2p[BPF_REG_3];
+	int bpf_tailcall_prologue_size = 8;
+
+	if (__is_defined(PPC64_ELF_ABI_v2))
+		bpf_tailcall_prologue_size += 4; /* skip past the toc load */
 
 	/*
 	 * if (index >= array->map.max_entries)
@@ -255,13 +260,8 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 
 	/* goto *(prog->bpf_func + prologue_size); */
 	PPC_BPF_LL(b2p[TMP_REG_1], b2p[TMP_REG_1], offsetof(struct bpf_prog, bpf_func));
-#ifdef PPC64_ELF_ABI_v1
-	/* skip past the function descriptor */
 	EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], b2p[TMP_REG_1],
-			FUNCTION_DESCR_SIZE + BPF_TAILCALL_PROLOGUE_SIZE));
-#else
-	EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], b2p[TMP_REG_1], BPF_TAILCALL_PROLOGUE_SIZE));
-#endif
+			FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
 	EMIT(PPC_RAW_MTCTR(b2p[TMP_REG_1]));
 
 	/* tear down stack, restore NVRs, ... */