netdev - [PATCH bpf-next v2 5/8] bpf, arm64: save 4 bytes of unneeded stack space

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Date:   Mon, 14 May 2018 23:22:31 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     alexei.starovoitov@...il.com
Cc:     netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH bpf-next v2 5/8] bpf, arm64: save 4 bytes of unneeded stack space

Follow-up to 816d9ef32a8b ("bpf, arm64: remove ld_abs/ld_ind") in
that the extra 4 byte JIT scratchpad is not needed anymore since it
was in ld_abs/ld_ind as stack buffer for bpf_load_pointer().

Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
---
 arch/arm64/net/bpf_jit_comp.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 0b40c8f..85113ca 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -21,7 +21,6 @@
 #include <linux/bpf.h>
 #include <linux/filter.h>
 #include <linux/printk.h>
-#include <linux/skbuff.h>
 #include <linux/slab.h>
 
 #include <asm/byteorder.h>
@@ -188,7 +187,7 @@ static int build_prologue(struct jit_ctx *ctx)
 	 *                        | ... | BPF prog stack
 	 *                        |     |
 	 *                        +-----+ <= (BPF_FP - prog->aux->stack_depth)
-	 *                        |RSVD | JIT scratchpad
+	 *                        |RSVD | padding
 	 * current A64_SP =>      +-----+ <= (BPF_FP - ctx->stack_size)
 	 *                        |     |
 	 *                        | ... | Function call stack
@@ -220,9 +219,7 @@ static int build_prologue(struct jit_ctx *ctx)
 		return -1;
 	}
 
-	/* 4 byte extra for skb_copy_bits buffer */
-	ctx->stack_size = prog->aux->stack_depth + 4;
-	ctx->stack_size = STACK_ALIGN(ctx->stack_size);
+	ctx->stack_size = STACK_ALIGN(prog->aux->stack_depth);
 
 	/* Set up function call stack */
 	emit(A64_SUB_I(1, A64_SP, A64_SP, ctx->stack_size), ctx);
-- 
2.9.5