[v2] linux: Fix a non-constant expression in _Static_assert

Message ID 20211008004643.532196-1-maskray@google.com
State New
Headers show
Series
  • [v2] linux: Fix a non-constant expression in _Static_assert
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Commit Message

According to C11 6.6p6, `const int` as an operand may not make up a
constant expression. GCC -O0 errors:

../sysdeps/unix/sysv/linux/opendir.c:107:19: error: static_assert expression is not an integral constant expression
  _Static_assert (allocation_size >= sizeof (struct dirent64),

-O2 -Wpedantic has a similar warning.
See https://gcc.gnu.org/PR102502 for GCC's inconsistency.

Use enum which is guaranteed to be a constant expression.
This also makes the file compilable with Clang.

Fixes: 4b962c9e859de23b461d61f860dbd3f21311e83a ("linux: Simplify opendir buffer allocation")
---
Changes from v1:
* Clarify commit message
* Reference https://gcc.gnu.org/PR102502 
---
 sysdeps/unix/sysv/linux/opendir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.33.0.882.g93a45727a2-goog

Comments

On Thu, Oct 7, 2021 at 5:46 PM Fangrui Song <maskray@google.com> wrote:
>

> According to C11 6.6p6, `const int` as an operand may not make up a

> constant expression. GCC -O0 errors:

>

> ../sysdeps/unix/sysv/linux/opendir.c:107:19: error: static_assert expression is not an integral constant expression

>   _Static_assert (allocation_size >= sizeof (struct dirent64),

>

> -O2 -Wpedantic has a similar warning.

> See https://gcc.gnu.org/PR102502 for GCC's inconsistency.

>

> Use enum which is guaranteed to be a constant expression.

> This also makes the file compilable with Clang.

>

> Fixes: 4b962c9e859de23b461d61f860dbd3f21311e83a ("linux: Simplify opendir buffer allocation")

> ---

> Changes from v1:

> * Clarify commit message

> * Reference https://gcc.gnu.org/PR102502

> ---

>  sysdeps/unix/sysv/linux/opendir.c | 2 +-

>  1 file changed, 1 insertion(+), 1 deletion(-)

>

> diff --git a/sysdeps/unix/sysv/linux/opendir.c b/sysdeps/unix/sysv/linux/opendir.c

> index 48f254d169..88640f44ee 100644

> --- a/sysdeps/unix/sysv/linux/opendir.c

> +++ b/sysdeps/unix/sysv/linux/opendir.c

> @@ -103,7 +103,7 @@ __alloc_dir (int fd, bool close_fd, int flags,

>       file system provides a bogus value.  */

>    enum { max_buffer_size = 1048576 };

>

> -  const size_t allocation_size = 32768;

> +  enum { allocation_size = 32768 };

>    _Static_assert (allocation_size >= sizeof (struct dirent64),

>                   "allocation_size < sizeof (struct dirent64)");

>

> --

> 2.33.0.882.g93a45727a2-goog

>


Gentle ping:)
Florian Weimer Oct. 15, 2021, 5:12 a.m. | #2
* Fangrui Song via Libc-alpha:

> diff --git a/sysdeps/unix/sysv/linux/opendir.c b/sysdeps/unix/sysv/linux/opendir.c

> index 48f254d169..88640f44ee 100644

> --- a/sysdeps/unix/sysv/linux/opendir.c

> +++ b/sysdeps/unix/sysv/linux/opendir.c

> @@ -103,7 +103,7 @@ __alloc_dir (int fd, bool close_fd, int flags,

>       file system provides a bogus value.  */

>    enum { max_buffer_size = 1048576 };

>  

> -  const size_t allocation_size = 32768;

> +  enum { allocation_size = 32768 };

>    _Static_assert (allocation_size >= sizeof (struct dirent64),

>  		  "allocation_size < sizeof (struct dirent64)");


Below we have:

  /* Increase allocation if requested, but not if the value appears to
     be bogus.  It will be between 32Kb and 1Mb.  */
  size_t allocation = MIN (MAX ((size_t) statp->st_blksize, allocation_size),
			   max_buffer_size);

Mixed-type MAX is a bit iffy, but we already have mixed-type MIN here,
so it probably does not matter.

Patch

diff --git a/sysdeps/unix/sysv/linux/opendir.c b/sysdeps/unix/sysv/linux/opendir.c
index 48f254d169..88640f44ee 100644
--- a/sysdeps/unix/sysv/linux/opendir.c
+++ b/sysdeps/unix/sysv/linux/opendir.c
@@ -103,7 +103,7 @@  __alloc_dir (int fd, bool close_fd, int flags,
      file system provides a bogus value.  */
   enum { max_buffer_size = 1048576 };
 
-  const size_t allocation_size = 32768;
+  enum { allocation_size = 32768 };
   _Static_assert (allocation_size >= sizeof (struct dirent64),
 		  "allocation_size < sizeof (struct dirent64)");