linux-kernel - [PATCH bpf-next] selftests/bpf: Fix compilation errors: assign a value to a constant

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Date:   Fri, 24 Feb 2023 23:00:53 +0800
From:   Rong Tao <rtoax@...mail.com>
To:     ast@...nel.org
Cc:     Rong Tao <rongtao@...tc.cn>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        bpf@...r.kernel.org (open list:BPF [GENERAL] (Safe Dynamic Programs and
        Tools)),
        linux-kselftest@...r.kernel.org (open list:KERNEL SELFTEST FRAMEWORK),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH bpf-next] selftests/bpf: Fix compilation errors: assign a value to a constant

From: Rong Tao <rongtao@...tc.cn>

Added bpf_find_vma test in commit f108662b27c9("selftests/bpf: Add tests
for bpf_find_vma") to assign values to variables that declare const in
find_vma_fail1.c programs, which is an error to the compiler and does not
test BPF verifiers. It is better to replace 'const vm_flags_t vm_flags'
with 'unsigned long vm_start' for testing.

    $ make -C tools/testing/selftests/bpf/ -j8
    ...
    progs/find_vma_fail1.c:16:16: error: cannot assign to non-static data
    member 'vm_flags' with const-qualified type 'const vm_flags_t' (aka
    'const unsigned long')
            vma->vm_flags |= 0x55;
            ~~~~~~~~~~~~~ ^
    ../tools/testing/selftests/bpf/tools/include/vmlinux.h:1898:20:
    note: non-static data member 'vm_flags' declared const here
                    const vm_flags_t vm_flags;
                    ~~~~~~~~~~~`~~~~~~^~~~~~~~

Signed-off-by: Rong Tao <rongtao@...tc.cn>
---
 tools/testing/selftests/bpf/progs/find_vma_fail1.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/find_vma_fail1.c b/tools/testing/selftests/bpf/progs/find_vma_fail1.c
index b3b326b8e2d1..47d5dedff554 100644
--- a/tools/testing/selftests/bpf/progs/find_vma_fail1.c
+++ b/tools/testing/selftests/bpf/progs/find_vma_fail1.c
@@ -13,7 +13,7 @@ static long write_vma(struct task_struct *task, struct vm_area_struct *vma,
 		      struct callback_ctx *data)
 {
 	/* writing to vma, which is illegal */
-	vma->vm_flags |= 0x55;
+	vma->vm_start = 0xffffffffff600000;
 
 	return 0;
 }
-- 
2.39.2