linux-kernel - Re: [PATCH v4] riscv: selftests: Fix warnings pointer masking test

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Message-ID: <20241206-6f0aafe057dc10df9a9e02a5@orel>
Date: Fri, 6 Dec 2024 10:15:17 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Shuah Khan <shuah@...nel.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Samuel Holland <samuel.holland@...ive.com>, Alexandre Ghiti <alex@...ti.fr>, linux-kselftest@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Palmer Dabbelt <palmer@...osinc.com>
Subject: Re: [PATCH v4] riscv: selftests: Fix warnings pointer masking test

On Thu, Dec 05, 2024 at 01:49:31PM -0800, Charlie Jenkins wrote:
> When compiling the pointer masking tests with -Wall this warning
> is present:
> 
> pointer_masking.c: In function ‘test_tagged_addr_abi_sysctl’:
> pointer_masking.c:203:9: warning: ignoring return value of ‘pwrite’
> declared with attribute ‘warn_unused_result’ [-Wunused-result]
>   203 |         pwrite(fd, &value, 1, 0); |
>       ^~~~~~~~~~~~~~~~~~~~~~~~ pointer_masking.c:208:9: warning:
> ignoring return value of ‘pwrite’ declared with attribute
> ‘warn_unused_result’ [-Wunused-result]
>   208 |         pwrite(fd, &value, 1, 0);
> 
> I came across this on riscv64-linux-gnu-gcc (Ubuntu
> 11.4.0-1ubuntu1~22.04).
> 
> Fix this by checking that the number of bytes written equal the expected
> number of bytes written.
> 
> Fixes: 7470b5afd150 ("riscv: selftests: Add a pointer masking test")
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> ---
> Changes in v4:
> - Skip sysctl_enabled test if first pwrite failed
> - Link to v3: https://lore.kernel.org/r/20241205-fix_warnings_pointer_masking_tests-v3-1-5c28b0f9640d@rivosinc.com
> 
> Changes in v3:
> - Fix sysctl enabled test case (Drew/Alex)
> - Move pwrite err condition into goto (Drew)
> - Link to v2: https://lore.kernel.org/r/20241204-fix_warnings_pointer_masking_tests-v2-1-1bf0c5095f58@rivosinc.com
> 
> Changes in v2:
> - I had ret != 2 for testing, I changed it to be ret != 1.
> - Link to v1: https://lore.kernel.org/r/20241204-fix_warnings_pointer_masking_tests-v1-1-ea1e9665ce7a@rivosinc.com
> ---
>  tools/testing/selftests/riscv/abi/pointer_masking.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/riscv/abi/pointer_masking.c b/tools/testing/selftests/riscv/abi/pointer_masking.c
> index dee41b7ee3e3..759445d5f265 100644
> --- a/tools/testing/selftests/riscv/abi/pointer_masking.c
> +++ b/tools/testing/selftests/riscv/abi/pointer_masking.c
> @@ -189,6 +189,8 @@ static void test_tagged_addr_abi_sysctl(void)
>  {
>  	char value;
>  	int fd;
> +	int ret;
> +	char *err_pwrite_msg = "failed to write to /proc/sys/abi/tagged_addr_disabled\n";
>  
>  	ksft_print_msg("Testing tagged address ABI sysctl\n");
>  
> @@ -200,18 +202,32 @@ static void test_tagged_addr_abi_sysctl(void)
>  	}
>  
>  	value = '1';
> -	pwrite(fd, &value, 1, 0);
> +	ret = pwrite(fd, &value, 1, 0);
> +	if (ret != 1) {
> +		ksft_test_result_skip(err_pwrite_msg);

It seems like we should have a better way to keep the count balanced than
to require a ksft_test_result_skip() call for each test on each error
path. Every time we add a test we'll have to go add skips everywhere else.

> +		goto err_pwrite;
> +	}
> +
>  	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == -EINVAL,
>  			 "sysctl disabled\n");
>  
>  	value = '0';
> -	pwrite(fd, &value, 1, 0);
> +	ret = pwrite(fd, &value, 1, 0);
> +	if (ret != 1)
> +		goto err_pwrite;
> +
>  	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == 0,
>  			 "sysctl enabled\n");
>  
>  	set_tagged_addr_ctrl(0, false);
>  
>  	close(fd);
> +
> +	return;
> +
> +err_pwrite:
> +	close(fd);
> +	ksft_test_result_fail(err_pwrite_msg);
>  }

I don't think the goto reduces much code or improves readability much. A
wrapper function should do better. I was thinking something like

 static bool pwrite_wrapper(int fd, void *buf, size_t count, const char *msg)
 {
   int ret = pwrite(fd, buf, count, 0);
   if (ret != count) {
      ksft_perror(msg);
      return false;
   }
   return true;
 }


 value = '1';
 if (!pwrite_wrapper(fd, &value, 1, "write '1'"))
    ksft_test_result_fail(...);

 value = '0';
 if (!pwrite_wrapper(fd, &value, 1, "write '0'"))
    ksft_test_result_fail(...);


>  
>  static void test_tagged_addr_abi_pmlen(int pmlen)
> 
> ---
> base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37
> change-id: 20241204-fix_warnings_pointer_masking_tests-3860e4f35429
> -- 
> - Charlie
> 

Thanks,
drew