bpf: arm64: fix uninitialized variable

From: Alexei Starovoitov <[email protected]>

fix the following issue:
arch/arm64/net/bpf_jit_comp.c: In function 'bpf_int_jit_compile':
arch/arm64/net/bpf_jit_comp.c:982:18: error: 'image_size' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Fixes db496944fdaa ("bpf: arm64: add JIT support for multi-function programs")

Reported-by Arnd Bergmann <[email protected]>

Signed-off-by Alexei Starovoitov <[email protected]>

---
 arch/arm64/net/bpf_jit_comp.c | 1 +
 1 file changed, 1 insertion(+)

arch/arm64/net/bpf_jit_comp.c +0 -0

index 396490cf7316..acaa935ed977 100644

Quoted 26 lines · Alexei Starovoitov

From: Alexei Starovoitov <[email protected]>

fix the following issue:
arch/arm64/net/bpf_jit_comp.c: In function 'bpf_int_jit_compile':
arch/arm64/net/bpf_jit_comp.c:982:18: error: 'image_size' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Fixes db496944fdaa ("bpf: arm64: add JIT support for multi-function programs")

Reported-by Arnd Bergmann <[email protected]>

Signed-off-by Alexei Starovoitov <[email protected]>

---
 arch/arm64/net/bpf_jit_comp.c | 1 +
 1 file changed, 1 insertion(+)

arch/arm64/net/bpf_jit_comp.c +1 -0

index 396490cf7316..acaa935ed977 100644
@@ -897,6 +897,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 		image_ptr = jit_data->image;
 		header = jit_data->header;
 		extra_pass = true;
+		image_size = sizeof(u32) * ctx.idx;
 		goto skip_init_ctx;
 	}
 	memset(&ctx, 0, sizeof(ctx));

Quoted 1 line

I don't really mind, but it feels more complex than it needs to be imho, since in the initial pass you fetch 'image_size' in fake pass from ctx.idx, then we set ctx.idx to 0 again, do another pass and use the cached ctx.idx from that second pass instead of the first one where we set 'image_size' originally, so we definitely need to take that into consideration in future reviews at least.

Quoted 26 lines · Daniel Borkmann

Quoted 25 lines · Alexei Starovoitov

From: Alexei Starovoitov <[email protected]>

fix the following issue:
arch/arm64/net/bpf_jit_comp.c: In function 'bpf_int_jit_compile':
arch/arm64/net/bpf_jit_comp.c:982:18: error: 'image_size' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Fixes db496944fdaa ("bpf: arm64: add JIT support for multi-function programs")

Reported-by Arnd Bergmann <[email protected]>

Signed-off-by Alexei Starovoitov <[email protected]>

---
 arch/arm64/net/bpf_jit_comp.c | 1 +

 1 file changed, 1 insertion(+)

arch/arm64/net/bpf_jit_comp.c +1 -0

index 396490cf7316..acaa935ed977 100644
@@ -897,6 +897,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
          image_ptr = jit_data->image;
          header = jit_data->header;
          extra_pass = true;
+        image_size = sizeof(u32) * ctx.idx;
          goto skip_init_ctx;
      }

Quoted 8 lines

arch/arm64/net/bpf_jit_comp.c struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) · line 903

Quoted 1 line

arch/arm64/net/bpf_jit_comp.c +0 -0

      memset(&ctx, 0, sizeof(ctx));

I don't really mind, but it feels more complex than it needs to be imho, since in the initial pass you fetch 'image_size' in fake pass from ctx.idx, then we set ctx.idx to 0 again, do another pass and use the cached ctx.idx from that second pass instead of the first one where we set 'image_size' originally, so we definitely need to take that into consideration in future reviews at least.

not sure what you mean.
This check: ctx.idx != jit_data->ctx.idx matters the most. After first alloc the 'image_size' variable used for dumping only. That's why the JITing itself worked fine. We could have removed it since it's computable from idx, but imo it's fine this way.