powerpc/bpf/32: No need to zeroise r4 when not doing tail call

r4 is cleared at function entry and used as tail call count.

But when the function does not perform tail call, r4 is
ignored, so no need to clear it.

Replace it by a NOP in that case.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9c5440b2b6d90a78600257433ac499b5c5101fbb.1675245773.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index a379b0ce19ffad4dc4e5140a0e50b940db3d708c..4e6caee9c98a28fb44cc345a477792e4bfa15ced 100644 (file)
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -114,7 +114,10 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
        int i;
 
        /* Initialize tail_call_cnt, to be skipped if we do tail calls. */
-       EMIT(PPC_RAW_LI(_R4, 0));
+       if (ctx->seen & SEEN_TAILCALL)
+               EMIT(PPC_RAW_LI(_R4, 0));
+       else
+               EMIT(PPC_RAW_NOP());
 
 #define BPF_TAILCALL_PROLOGUE_SIZE     4