powerpc/bpf: Skip branch range validation during first pass

During the first pass, addrs[] is still being populated. So, all
branches to following instructions will appear to be going to the start
of the JIT program. Ignore branch range validation for such instructions
and assume those to be in range. Branch range validation will happen
during the second pass after addrs[] is setup properly.
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/bc517413d11636e20dbfc88503dad14bcbe391e2.1644834730.git.naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/net/bpf_jit.h

@@ -27,7 +27,7 @@
 #define PPC_JMP(dest)							      \
 	do {								      \
 		long offset = (long)(dest) - (ctx->idx * 4);		      \
-		if (!is_offset_in_branch_range(offset)) {		      \
+		if ((dest) != 0 && !is_offset_in_branch_range(offset)) {		      \
 			pr_err_ratelimited("Branch offset 0x%lx (@%u) out of range\n", offset, ctx->idx);			\
 			return -ERANGE;					      \
 		}							      \
@@ -41,7 +41,7 @@
 #define PPC_BCC_SHORT(cond, dest)					      \
 	do {								      \
 		long offset = (long)(dest) - (ctx->idx * 4);		      \
-		if (!is_offset_in_cond_branch_range(offset)) {		      \
+		if ((dest) != 0 && !is_offset_in_cond_branch_range(offset)) {		      \
 			pr_err_ratelimited("Conditional branch offset 0x%lx (@%u) out of range\n", offset, ctx->idx);		\
 			return -ERANGE;					      \
 		}							      \