[PATCH 2/5] include: Replace zero-length array "msg" with C99 flexible-array.

[PATCH 2/5] include: Replace zero-length array "msg" with C99 flexible-array.

[Cristian Rodríguez]

Signed-off-by: Cristian Rodríguez <cristian@rodriguez.im>
---
 include/stdlib.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/stdlib.h b/include/stdlib.h
index 7deb8193d7..206ceb7435 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -360,7 +360,7 @@ libc_hidden_proto (__qfcvt_r)
 struct abort_msg_s
 {
   unsigned int size;
-  char msg[0];
+  char msg[];
 };
 extern struct abort_msg_s *__abort_msg;
 libc_hidden_proto (__abort_msg)
-- 
2.41.0

[PATCH 3/5] linux: Replace zero-length array with flexible-array member on inotify struct

[Cristian Rodríguez]

Current kernel versions require a compiler supporting -std=gnu11
and therefore supporting C99 flexible arrays. old versions require
a c89 compiler supporting this feature as an extension.

Signed-off-by: Cristian Rodríguez <cristian@rodriguez.im>
---
 sysdeps/unix/sysv/linux/sys/inotify.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/unix/sysv/linux/sys/inotify.h b/sysdeps/unix/sysv/linux/sys/inotify.h
index 1e8e68cd97..535f57e27b 100644
--- a/sysdeps/unix/sysv/linux/sys/inotify.h
+++ b/sysdeps/unix/sysv/linux/sys/inotify.h
@@ -31,7 +31,7 @@ struct inotify_event
   uint32_t mask;	/* Watch mask.  */
   uint32_t cookie;	/* Cookie to synchronize two events.  */
   uint32_t len;		/* Length (including NULs) of name.  */
-  char name __flexarr;	/* Name.  */
+  char name[];		/* Name.  */
 };
 
 
-- 
2.41.0

[PATCH 4/5] linux: Replace zero-length array with flexible-array member on struct dirstream

[Cristian Rodríguez]

The linux kernel has always required a compiler supporting c99
flexible-arrays.

Signed-off-by: Cristian Rodríguez <cristian@rodriguez.im>
---
 sysdeps/unix/sysv/linux/dirstream.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/unix/sysv/linux/dirstream.h b/sysdeps/unix/sysv/linux/dirstream.h
index 3cb313b410..20ce7d1347 100644
--- a/sysdeps/unix/sysv/linux/dirstream.h
+++ b/sysdeps/unix/sysv/linux/dirstream.h
@@ -47,7 +47,7 @@ struct __dirstream
        sufficient because dirents on 32-bit platforms can require
        64-bit alignment.  We use "long double" here to be consistent
        with what malloc uses.  */
-    char data[0] __attribute__ ((aligned (__alignof__ (long double))));
+    char data[] __attribute_nonstring__ __attribute__ ((aligned (__alignof__ (long double))));
   };
 
 #define _DIR_dirfd(dirp)	((dirp)->fd)
-- 
2.41.0

[PATCH 5/5] stdio-common: Replace zero-length array with flexible-array member

[Cristian Rodríguez]

Signed-off-by: Cristian Rodríguez <cristian@rodriguez.im>
---
 stdio-common/reg-modifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stdio-common/reg-modifier.c b/stdio-common/reg-modifier.c
index a52022d1ba..d957d85a5f 100644
--- a/stdio-common/reg-modifier.c
+++ b/stdio-common/reg-modifier.c
@@ -27,7 +27,7 @@ struct printf_modifier_record
 {
   struct printf_modifier_record *next;
   int bit;
-  wchar_t str[0];
+  wchar_t str[];
 };
 
 struct printf_modifier_record **__printf_modifier_table attribute_hidden;
-- 
2.41.0

Re: [PATCH 3/5] linux: Replace zero-length array with flexible-array member on inotify struct

[Cristian Rodríguez]

[-- Attachment #1: Type: text/plain, Size: 1094 bytes --]

This patch only syncs with the current kernel headers.

On Wed, Jun 21, 2023 at 5:35 PM Cristian Rodríguez <cristian@rodriguez.im>
wrote:

> Current kernel versions require a compiler supporting -std=gnu11
> and therefore supporting C99 flexible arrays. old versions require
> a c89 compiler supporting this feature as an extension.
>
> Signed-off-by: Cristian Rodríguez <cristian@rodriguez.im>
> ---
>  sysdeps/unix/sysv/linux/sys/inotify.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sysdeps/unix/sysv/linux/sys/inotify.h
> b/sysdeps/unix/sysv/linux/sys/inotify.h
> index 1e8e68cd97..535f57e27b 100644
> --- a/sysdeps/unix/sysv/linux/sys/inotify.h
> +++ b/sysdeps/unix/sysv/linux/sys/inotify.h
> @@ -31,7 +31,7 @@ struct inotify_event
>    uint32_t mask;       /* Watch mask.  */
>    uint32_t cookie;     /* Cookie to synchronize two events.  */
>    uint32_t len;                /* Length (including NULs) of name.  */
> -  char name __flexarr; /* Name.  */
> +  char name[];         /* Name.  */
>  };
>
>
> --
> 2.41.0
>
>

Re: [PATCH 3/5] linux: Replace zero-length array with flexible-array member on inotify struct

[Florian Weimer]

* Cristian Rodríguez via Libc-alpha:

> Current kernel versions require a compiler supporting -std=gnu11
> and therefore supporting C99 flexible arrays. old versions require
> a c89 compiler supporting this feature as an extension.

Ugh, you are right:

commit 94dfc73e7cf4a31da66b8843f0b9283ddd6b8381
Author: Gustavo A. R. Silva <gustavoars@kernel.org>
Date:   Wed Apr 6 19:36:51 2022 -0500

    treewide: uapi: Replace zero-length arrays with flexible-array members

It's specifically targeting UAPI headers, so it's not a (harmless)
kernel-internal change.

Do you know if anyone has looked at the compatibility impact of this
change on C parsers?  I'm not sure if we can do the same thing.  In
particular, if kernel headers are not C89-compatible, we may have to add
kludges to our own headers that avoid including them in C89 mode.

Thanks,
Florian

Re: [PATCH 4/5] linux: Replace zero-length array with flexible-array member on struct dirstream

[Florian Weimer]

* Cristian Rodríguez via Libc-alpha:

> The linux kernel has always required a compiler supporting c99
> flexible-arrays.

This is not an installed header, so this commit message is misleading.
Why __attribute_nonstring__?

Thanks,
Florian

Re: [PATCH 4/5] linux: Replace zero-length array with flexible-array member on struct dirstream

[Cristian Rodríguez]

[-- Attachment #1: Type: text/plain, Size: 495 bytes --]

On Thu, Jun 22, 2023 at 1:25 AM Florian Weimer <fweimer@redhat.com> wrote:

> * Cristian Rodríguez via Libc-alpha:
>
> > The linux kernel has always required a compiler supporting c99
> > flexible-arrays.
>
> This is not an installed header, so this commit message is misleading.
> Why __attribute_nonstring__?
>
>
>
So there is a warning if someone, by a mistake obviously.,,treats it as an
string or calls any str* function on it.. data is filled with struct
linux_dirent  s

Re: [PATCH 3/5] linux: Replace zero-length array with flexible-array member on inotify struct

[Cristian Rodríguez]

[-- Attachment #1: Type: text/plain, Size: 638 bytes --]

On Thu, Jun 22, 2023 at 1:23 AM Florian Weimer <fweimer@redhat.com> wrote:

>
> Do you know if anyone has looked at the compatibility impact of this
> change on C parsers?  I'm not sure if we can do the same thing.  In
> particular, if kernel headers are not C89-compatible, we may have to add
> kludges to our own headers that avoid including them in C89 mode.
>
>
>
On this case it is a linux feature, which has required this as an
extension, probably since forever. I have only checked kernel 3.2 as the
minimum and that version indeed uses c99 flex arrays at least *internally*
(I have not checked all headers though)