[PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[Thomas Huth]

If I configure my build with --enable-sanitizers, my GCC (v8.5.0)
complains:

.../softmmu/device_tree.c: In function ‘qemu_fdt_add_path’:
.../softmmu/device_tree.c:560:18: error: ‘retval’ may be used uninitialized
 in this function [-Werror=maybe-uninitialized]
     int namelen, retval;
                  ^~~~~~

It's a false warning since the while loop is always executed at least
once (p has to be non-NULL, otherwise the derefence in the if-statement
earlier will crash). Thus let's switch to a do-while loop here instead
to make the compiler happy in all cases.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 softmmu/device_tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
index 3965c834ca..9e96f5ecd5 100644
--- a/softmmu/device_tree.c
+++ b/softmmu/device_tree.c
@@ -564,7 +564,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
         return -1;
     }
 
-    while (p) {
+    do {
         name = p + 1;
         p = strchr(name, '/');
         namelen = p != NULL ? p - name : strlen(name);
@@ -584,7 +584,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
         }
 
         parent = retval;
-    }
+    } while (p);
 
     return retval;
 }
-- 
2.27.0

Re: [PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[Andrew Jones]

On Fri, Jan 07, 2022 at 02:38:44PM +0100, Thomas Huth wrote:
> If I configure my build with --enable-sanitizers, my GCC (v8.5.0)
> complains:
> 
> .../softmmu/device_tree.c: In function ‘qemu_fdt_add_path’:
> .../softmmu/device_tree.c:560:18: error: ‘retval’ may be used uninitialized
>  in this function [-Werror=maybe-uninitialized]
>      int namelen, retval;
>                   ^~~~~~
> 
> It's a false warning since the while loop is always executed at least
> once (p has to be non-NULL, otherwise the derefence in the if-statement
> earlier will crash). Thus let's switch to a do-while loop here instead
> to make the compiler happy in all cases.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  softmmu/device_tree.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> index 3965c834ca..9e96f5ecd5 100644
> --- a/softmmu/device_tree.c
> +++ b/softmmu/device_tree.c
> @@ -564,7 +564,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>          return -1;
>      }
>  
> -    while (p) {
> +    do {
>          name = p + 1;
>          p = strchr(name, '/');
>          namelen = p != NULL ? p - name : strlen(name);
> @@ -584,7 +584,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>          }
>  
>          parent = retval;
> -    }
> +    } while (p);
>  
>      return retval;
>  }
> -- 
> 2.27.0
>

 
Reviewed-by: Andrew Jones <drjones@redhat.com>

Re: [PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[Philippe Mathieu-Daudé]

On 7/1/22 14:38, Thomas Huth wrote:
> If I configure my build with --enable-sanitizers, my GCC (v8.5.0)
> complains:
> 
> .../softmmu/device_tree.c: In function ‘qemu_fdt_add_path’:
> .../softmmu/device_tree.c:560:18: error: ‘retval’ may be used uninitialized
>   in this function [-Werror=maybe-uninitialized]
>       int namelen, retval;
>                    ^~~~~~
> 
> It's a false warning since the while loop is always executed at least
> once (p has to be non-NULL, otherwise the derefence in the if-statement
> earlier will crash). Thus let's switch to a do-while loop here instead
> to make the compiler happy in all cases.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   softmmu/device_tree.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Re: [PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[Richard Henderson]

On 1/7/22 5:38 AM, Thomas Huth wrote:
> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> index 3965c834ca..9e96f5ecd5 100644
> --- a/softmmu/device_tree.c
> +++ b/softmmu/device_tree.c
> @@ -564,7 +564,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>           return -1;
>       }
>   
> -    while (p) {
> +    do {
>           name = p + 1;
>           p = strchr(name, '/');
>           namelen = p != NULL ? p - name : strlen(name);
> @@ -584,7 +584,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>           }
>   
>           parent = retval;
> -    }
> +    } while (p);

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

In addition, the copy between 'path' and 'p' is unnecessary -- one of the variables should 
be removed.  Either rename the parameter to 'p', or rename all uses to 'path'.


r~

Re: [PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[Alistair Francis]

On Fri, Jan 7, 2022 at 11:41 PM Thomas Huth <thuth@redhat.com> wrote:
>
> If I configure my build with --enable-sanitizers, my GCC (v8.5.0)
> complains:
>
> .../softmmu/device_tree.c: In function ‘qemu_fdt_add_path’:
> .../softmmu/device_tree.c:560:18: error: ‘retval’ may be used uninitialized
>  in this function [-Werror=maybe-uninitialized]
>      int namelen, retval;
>                   ^~~~~~
>
> It's a false warning since the while loop is always executed at least
> once (p has to be non-NULL, otherwise the derefence in the if-statement
> earlier will crash). Thus let's switch to a do-while loop here instead
> to make the compiler happy in all cases.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  softmmu/device_tree.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> index 3965c834ca..9e96f5ecd5 100644
> --- a/softmmu/device_tree.c
> +++ b/softmmu/device_tree.c
> @@ -564,7 +564,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>          return -1;
>      }
>
> -    while (p) {
> +    do {
>          name = p + 1;
>          p = strchr(name, '/');
>          namelen = p != NULL ? p - name : strlen(name);
> @@ -584,7 +584,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>          }
>
>          parent = retval;
> -    }
> +    } while (p);
>
>      return retval;
>  }
> --
> 2.27.0
>
>

Re: [PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[wangyanan (Y) via]

On 2022/1/7 21:38, Thomas Huth wrote:
> If I configure my build with --enable-sanitizers, my GCC (v8.5.0)
> complains:
>
> .../softmmu/device_tree.c: In function ‘qemu_fdt_add_path’:
> .../softmmu/device_tree.c:560:18: error: ‘retval’ may be used uninitialized
>   in this function [-Werror=maybe-uninitialized]
>       int namelen, retval;
>                    ^~~~~~
>
> It's a false warning since the while loop is always executed at least
> once (p has to be non-NULL, otherwise the derefence in the if-statement
> earlier will crash). Thus let's switch to a do-while loop here instead
> to make the compiler happy in all cases.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   softmmu/device_tree.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
Reviewed-by: Yanan Wang <wangyanan55@huawei.com>
> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> index 3965c834ca..9e96f5ecd5 100644
> --- a/softmmu/device_tree.c
> +++ b/softmmu/device_tree.c
> @@ -564,7 +564,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>           return -1;
>       }
>   
> -    while (p) {
> +    do {
>           name = p + 1;
>           p = strchr(name, '/');
>           namelen = p != NULL ? p - name : strlen(name);
> @@ -584,7 +584,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>           }
>   
>           parent = retval;
> -    }
> +    } while (p);
>   
>       return retval;
>   }

Re: [PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[wangyanan (Y) via]

On 2022/1/8 4:18, Richard Henderson wrote:
> On 1/7/22 5:38 AM, Thomas Huth wrote:
>> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
>> index 3965c834ca..9e96f5ecd5 100644
>> --- a/softmmu/device_tree.c
>> +++ b/softmmu/device_tree.c
>> @@ -564,7 +564,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>>           return -1;
>>       }
>>   -    while (p) {
>> +    do {
>>           name = p + 1;
>>           p = strchr(name, '/');
>>           namelen = p != NULL ? p - name : strlen(name);
>> @@ -584,7 +584,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>>           }
>>             parent = retval;
>> -    }
>> +    } while (p);
>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>
> In addition, the copy between 'path' and 'p' is unnecessary -- one of 
> the variables should be removed.  Either rename the parameter to 'p', 
> or rename all uses to 'path'.
>
Yes. We can simply remove "const char *p = path;" and directly
using the parameter "path" passed in would be fine enough.
Thanks for catching this.

Thanks,
Yanan
>
> r~
> .

Re: [PATCH] softmmu/device_tree: Silence compiler warning with --enable-sanitizers

[Alistair Francis]

On Fri, Jan 7, 2022 at 11:41 PM Thomas Huth <thuth@redhat.com> wrote:
>
> If I configure my build with --enable-sanitizers, my GCC (v8.5.0)
> complains:
>
> .../softmmu/device_tree.c: In function ‘qemu_fdt_add_path’:
> .../softmmu/device_tree.c:560:18: error: ‘retval’ may be used uninitialized
>  in this function [-Werror=maybe-uninitialized]
>      int namelen, retval;
>                   ^~~~~~
>
> It's a false warning since the while loop is always executed at least
> once (p has to be non-NULL, otherwise the derefence in the if-statement
> earlier will crash). Thus let's switch to a do-while loop here instead
> to make the compiler happy in all cases.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Thanks!

Applied to riscv-to-apply.next

If anyone else (trivial maybe?) wants to take this feel free to as
well, otherwise I'll just take this via the RISC-V tree.

Alistair

> ---
>  softmmu/device_tree.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> index 3965c834ca..9e96f5ecd5 100644
> --- a/softmmu/device_tree.c
> +++ b/softmmu/device_tree.c
> @@ -564,7 +564,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>          return -1;
>      }
>
> -    while (p) {
> +    do {
>          name = p + 1;
>          p = strchr(name, '/');
>          namelen = p != NULL ? p - name : strlen(name);
> @@ -584,7 +584,7 @@ int qemu_fdt_add_path(void *fdt, const char *path)
>          }
>
>          parent = retval;
> -    }
> +    } while (p);
>
>      return retval;
>  }
> --
> 2.27.0
>
>