Re: [PATCH] Add build time guard to detect off_t mismatch

On 07.05.26 14:23, Richard Weinberger wrote:
> When Xenomai is built without _FILE_OFFSET_BITS=64 on a 32 bit system,
> which is the default, but the Xenomai application itself is built later
> with _FILE_OFFSET_BITS=64, we get a nasty ABI mismatch. Since only very
> few cobalt syscalls use off_t, the mismatch goes undiscovered for a
> surprisingly long time. In my case it surfaced only after a realtime
> application which uses mmap() failed sometimes at mmap() depending on
> what functions it called before mmap(). In the good cases it used to
> work by chance since the extra bytes used for off_t on the stack were
> zero.
> 
> To save the next person in the same situation a lot of time, compute
> the size of off_t at configure time and compare it against the
> application's sizeof(off_t) via a static assertion in a new generated
> header, which is included when building Xenomai applications.
> 

This should have been resolved (but apparently we missed most of it) by
0bb6608b6fa7129de1ff4213ddf31298616cbf23. Can you name some of the
remaining mismatches?

Jan

> Signed-off-by: Richard Weinberger <[email protected]>
> ---
>  .gitignore                     |  1 +
>  configure.ac                   |  4 ++++
>  include/Makefile.am            |  2 +-
>  include/boilerplate/libc.h     |  1 +
>  include/xeno_off_t_assert.h.in | 10 ++++++++++
>  5 files changed, 17 insertions(+), 1 deletion(-)
>  create mode 100644 include/xeno_off_t_assert.h.in
> 
> diff --git a/.gitignore b/.gitignore
> index 402604c59..8b35071c9 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -26,6 +26,7 @@
>  /configure
>  /include/stamp-h?
>  /libtool
> +/include/xeno_off_t_assert.h
>  /include/xeno_config.h
>  /include/xeno_config.h.in*
>  /.ccache
> diff --git a/configure.ac b/configure.ac
> index 0d6dd87b6..b3d08d6f0 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -19,6 +19,10 @@ if test x$prefix = xNONE; then
>     prefix=$ac_default_prefix
>  fi
>  
> +AC_CHECK_SIZEOF([off_t])
> +AC_SUBST([SIZEOF_OFF_T], [$ac_cv_sizeof_off_t])
> +AC_CONFIG_FILES([include/xeno_off_t_assert.h])
> +
>  version_code=`cat $srcdir/config/version-code`
>  CONFIG_XENO_VERSION_MAJOR=`expr $version_code : '\([[0-9]]*\)'`
>  CONFIG_XENO_VERSION_MINOR=`expr $version_code : '[[0-9]]*\.\([[0-9]]*\)'`
> diff --git a/include/Makefile.am b/include/Makefile.am
> index 1e9fe0210..05dda9539 100644
> --- a/include/Makefile.am
> +++ b/include/Makefile.am
> @@ -1,4 +1,4 @@
> -nodist_include_HEADERS=$(CONFIG_HEADER)
> +nodist_include_HEADERS=$(CONFIG_HEADER) $(top_builddir)/include/xeno_off_t_assert.h
>  
>  SUBDIRS = 		\
>  	boilerplate	\
> diff --git a/include/boilerplate/libc.h b/include/boilerplate/libc.h
> index 44ddad5af..98d49648a 100644
> --- a/include/boilerplate/libc.h
> +++ b/include/boilerplate/libc.h
> @@ -19,6 +19,7 @@
>  #define _BOILERPLATE_LIBC_H
>  
>  #include <limits.h>
> +#include <xeno_off_t_assert.h>
>  
>  #ifdef __IN_XENO__
>  /*
> diff --git a/include/xeno_off_t_assert.h.in b/include/xeno_off_t_assert.h.in
> new file mode 100644
> index 000000000..29b544b29
> --- /dev/null
> +++ b/include/xeno_off_t_assert.h.in
> @@ -0,0 +1,10 @@
> +#ifndef XENO_OFF_T_ASSERT_H
> +#define XENO_OFF_T_ASSERT_H
> +
> +#include <sys/types.h>
> +
> +#define SIZEOF_OFF_T @SIZEOF_OFF_T@
> +
> +_Static_assert(SIZEOF_OFF_T == sizeof(off_t), "off_t size mismatch");
> +
> +#endif /* XENO_OFF_T_ASSERT_H */


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