Re: [PATCH bpf-next 3/3] selftests/bpf: Add tests for get_func_[arg|ret|arg_cnt] helpers

On Tue, Dec 07, 2021 at 02:54:33PM -0800, Andrii Nakryiko wrote:

SNIP

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+__u64 test1_result = 0;
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(test1)
+{
+   __u64 cnt = bpf_get_func_arg_cnt(ctx);
+   __u64 a = 0, z = 0, ret = 0;
+   __s64 err;
+
+   test1_result = cnt == 1;
+
+   /* valid arguments */
+   err = bpf_get_func_arg(ctx, 0, &a);
+   test1_result &= err == 0 && (int) a == 1;

int cast unnecessary? but some ()'s wouldn't hurt...

it is, 'a' is int and trampoline saves it with 32-bit register like:

  mov    %edi,-0x8(%rbp)

so the upper 4 bytes are not zeroed

oh, this is definitely worth a comment, it's quite a big gotcha we'll
need to remember

ok, will add comment for that

jirka

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+
+   /* not valid argument */
+   err = bpf_get_func_arg(ctx, 1, &z);
+   test1_result &= err == -EINVAL;
+
+   /* return value fails in fentry */
+   err = bpf_get_func_ret(ctx, &ret);
+   test1_result &= err == -EINVAL;
+   return 0;
+}
+
+__u64 test2_result = 0;
+SEC("fexit/bpf_fentry_test2")
+int BPF_PROG(test2)
+{
+   __u64 cnt = bpf_get_func_arg_cnt(ctx);
+   __u64 a = 0, b = 0, z = 0, ret = 0;
+   __s64 err;
+
+   test2_result = cnt == 2;
+
+   /* valid arguments */
+   err = bpf_get_func_arg(ctx, 0, &a);
+   test2_result &= err == 0 && (int) a == 2;
+
+   err = bpf_get_func_arg(ctx, 1, &b);
+   test2_result &= err == 0 && b == 3;
+
+   /* not valid argument */
+   err = bpf_get_func_arg(ctx, 2, &z);
+   test2_result &= err == -EINVAL;
+
+   /* return value */
+   err = bpf_get_func_ret(ctx, &ret);
+   test2_result &= err == 0 && ret == 5;
+   return 0;
+}
+
+__u64 test3_result = 0;
+SEC("fmod_ret/bpf_modify_return_test")
+int BPF_PROG(fmod_ret_test, int _a, int *_b, int _ret)
+{
+   __u64 cnt = bpf_get_func_arg_cnt(ctx);
+   __u64 a = 0, b = 0, z = 0, ret = 0;
+   __s64 err;
+
+   test3_result = cnt == 2;
+
+   /* valid arguments */
+   err = bpf_get_func_arg(ctx, 0, &a);
+   test3_result &= err == 0 && (int) a == 1;
+
+   err = bpf_get_func_arg(ctx, 1, &b);
+   test3_result &= err == 0;

why no checking of b value here?

right, ok

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+
+   /* not valid argument */
+   err = bpf_get_func_arg(ctx, 2, &z);
+   test3_result &= err == -EINVAL;
+
+   /* return value */
+   err = bpf_get_func_ret(ctx, &ret);
+   test3_result &= err == 0 && ret == 0;
+   return 1234;
+}
+
+__u64 test4_result = 0;
+SEC("fexit/bpf_modify_return_test")
+int BPF_PROG(fexit_test, int _a, __u64 _b, int _ret)
+{
+   __u64 cnt = bpf_get_func_arg_cnt(ctx);
+   __u64 a = 0, b = 0, z = 0, ret = 0;
+   __s64 err;
+
+   test4_result = cnt == 2;
+
+   /* valid arguments */
+   err = bpf_get_func_arg(ctx, 0, &a);
+   test4_result &= err == 0 && (int) a == 1;
+
+   err = bpf_get_func_arg(ctx, 1, &b);
+   test4_result &= err == 0;

same, for consistency, b should have been checked, no?

ok

thanks,
jirka