[PATCH bpf-next v3 2/2] bpf, arm64: calculate offset as byte-offset for bpf line info

[Hou Tao]

insn_to_jit_off passed to bpf_prog_fill_jited_linfo() is calculated
in instruction granularity instead of bytes granularity, but bpf
line info requires byte offset, so fixing it by calculating ctx->offset
as byte-offset. bpf2a64_offset() needs to return relative instruction
offset by using ctx->offfset, so update it accordingly.

Fixes: 37ab566c178d ("bpf: arm64: Enable arm64 jit to provide bpf_line_info")
Signed-off-by: Hou Tao <houtao1 at huawei.com>
---
 arch/arm64/net/bpf_jit_comp.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 68b35c83e637..aed07cba78ec 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -164,9 +164,14 @@ static inline int bpf2a64_offset(int bpf_insn, int off,
 	/*
 	 * Whereas arm64 branch instructions encode the offset
 	 * from the branch itself, so we must subtract 1 from the
-	 * instruction offset.
+	 * instruction offset. The unit of ctx->offset is byte, so
+	 * subtract AARCH64_INSN_SIZE from it. bpf2a64_offset()
+	 * returns instruction offset, so divide by AARCH64_INSN_SIZE
+	 * at the end.
 	 */
-	return ctx->offset[bpf_insn + off] - (ctx->offset[bpf_insn] - 1);
+	return (ctx->offset[bpf_insn + off] -
+		(ctx->offset[bpf_insn] - AARCH64_INSN_SIZE)) /
+		AARCH64_INSN_SIZE;
 }
 
 static void jit_fill_hole(void *area, unsigned int size)
@@ -1087,13 +1092,14 @@ static int build_body(struct jit_ctx *ctx, bool extra_pass)
 		const struct bpf_insn *insn = &prog->insnsi[i];
 		int ret;
 
+		/* BPF line info needs byte-offset instead of insn-offset */
 		if (ctx->image == NULL)
-			ctx->offset[i] = ctx->idx;
+			ctx->offset[i] = ctx->idx * AARCH64_INSN_SIZE;
 		ret = build_insn(insn, ctx, extra_pass);
 		if (ret > 0) {
 			i++;
 			if (ctx->image == NULL)
-				ctx->offset[i] = ctx->idx;
+				ctx->offset[i] = ctx->idx * AARCH64_INSN_SIZE;
 			continue;
 		}
 		if (ret)
@@ -1105,7 +1111,7 @@ static int build_body(struct jit_ctx *ctx, bool extra_pass)
 	 * instruction (end of program)
 	 */
 	if (ctx->image == NULL)
-		ctx->offset[i] = ctx->idx;
+		ctx->offset[i] = ctx->idx * AARCH64_INSN_SIZE;
 
 	return 0;
 }
-- 
2.27.0