Florian Weimer wrote:
Just to be clear, you looked at the wrong struct dirent definition for
GNU/Linux, there is a sysdeps override.
Yes, we'd need a similar fix in sysdeps/unix/sysv/linux/bits/dirent.h.
Right now, most programs relying on sizeof (struct dirent) work well in
almost all cases. We really don't want to break that. There appears to
be an overlap between these programs and users of readdir_r, so once we
remove that from the API, we should have better story for struct dirent
declarators as well.
I see your point in worrying about GNU/Linux programs that use 'sizeof
(struct dirent)', even though these programs are not portable and won't
work on other POSIX platforms.
How about something like the attached (untested) patch, then? It keeps
the structure the same size, while still using flexible arrays to
indicate to analyzers that the array in question may be larger. It also
adds a compile-time option (default off) to simply use flexible arrays
without the backwards-compatibility hack. We could use that option in
Gnulib.
diff --git a/bits/dirent.h b/bits/dirent.h
index 7b79a53..69a7892 100644
--- a/bits/dirent.h
+++ b/bits/dirent.h
@@ -32,7 +32,7 @@ struct dirent
unsigned char d_namlen; /* Length of the file name. */
/* Only this member is in the POSIX standard. */
- char d_name[1]; /* File name (actually longer). */
+ __flexarray (d_name, char, 1); /* File name. */
};
#ifdef __USE_LARGEFILE64
@@ -42,8 +42,7 @@ struct dirent64
unsigned short int d_reclen;
unsigned char d_type;
unsigned char d_namlen;
-
- char d_name[1];
+ __flexarray (d_name, char, 1); /* File name. */
};
#endif
diff --git a/include/features.h b/include/features.h
index 9514d35..ca162d3 100644
--- a/include/features.h
+++ b/include/features.h
@@ -45,6 +45,7 @@
_THREAD_SAFE Same as _REENTRANT, often used by other systems.
_FORTIFY_SOURCE If set to numeric value > 0 additional security
measures are defined, according to level.
+ _FLEXARRAY_SOURCE Select flexible array data structures when applicable.
The `-ansi' switch to the GNU C compiler, and standards conformance
options such as `-std=c99', define __STRICT_ANSI__. If none of
@@ -80,6 +81,7 @@
__USE_GNU Define GNU extensions.
__USE_REENTRANT Define reentrant/thread-safe *_r functions.
__USE_FORTIFY_LEVEL Additional security measures used, according to level.
+ __USE_FLEXARRAY Use flexible arrays for data structures.
The macros `__GNU_LIBRARY__', `__GLIBC__', and `__GLIBC_MINOR__' are
defined by this file unconditionally. `__GNU_LIBRARY__' is provided
@@ -117,6 +119,7 @@
#undef __USE_GNU
#undef __USE_REENTRANT
#undef __USE_FORTIFY_LEVEL
+#undef __USE_FLEXARRAY
#undef __KERNEL_STRICT_NAMES
/* Suppress kernel-name space pollution unless user expressedly asks
@@ -341,6 +344,10 @@
# define __USE_FORTIFY_LEVEL 0
#endif
+#ifdef _FLEXARRAY_SOURCE
+# define __USE_FLEXARRAY 1
+#endif
+
/* Get definitions of __STDC_* predefined macros, if the compiler has
not preincluded this header automatically. */
#include <stdc-predef.h>
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 7fd4154..facfdc3 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -157,10 +157,29 @@
# else
/* Some other non-C99 compiler. Approximate with [1]. */
# define __flexarr [1]
+# define __flexarray(id, type, size) type id[size]
# endif
# endif
#endif
+/* Declare a structure member named ID, with type "array of TYPE", and
+ with actual size unspecified but with nominal size SIZE for the
+ benefit of traditional applications. If the application is
+ compiled with _FLEXARRAY_SOURCE and if the compiler is C99 or
+ better, model this as a flexible array. Otherwise, model it as a
+ fixed-size array of size SIZE (followed by a flexible array
+ afterwards, if C99, for the benefit of source-code analyzers that
+ can use this as a cue that the array is really varying-size). The
+ fixed-size array is for compatibility with programs that unwisely
+ take the size of structures that contain flexible arrays, and which
+ rely on traditional glibc which uses fixed-size arrays. */
+#ifndef __flexarray
+# ifdef __USE_FLEXARRAY
+# define __flexarray(id, type, size) type id[]
+# else
+# define __flexarray(id, type, size) type id[size]; type __flexarray __flexarr
+# endif
+#endif
/* __asm__ ("xyz") is used throughout the headers to rename functions
at the assembly language level. This is wrapped by the __REDIRECT
diff --git a/sysdeps/nacl/bits/dirent.h b/sysdeps/nacl/bits/dirent.h
index d4eb7fe..2e38a58 100644
--- a/sysdeps/nacl/bits/dirent.h
+++ b/sysdeps/nacl/bits/dirent.h
@@ -30,7 +30,7 @@ struct dirent
unsigned short int d_reclen; /* Length of the whole `struct dirent'. */
/* Only this member is in the POSIX standard. */
- char d_name[256]; /* We must not include limits.h! */
+ __flexarray (d_name, char, 256); /* We must not include limits.h! */
};
#ifdef __USE_LARGEFILE64
@@ -42,7 +42,7 @@ struct dirent64
unsigned short int d_reclen; /* Length of the whole `struct dirent'. */
/* Only this member is in the POSIX standard. */
- char d_name[256]; /* We must not include limits.h! */
+ __flexarray (d_name, char, 256); /* We must not include limits.h! */
};
#endif
diff --git a/sysdeps/unix/sysv/linux/alpha/bits/dirent.h b/sysdeps/unix/sysv/linux/alpha/bits/dirent.h
index 98d297e..2470d0f 100644
--- a/sysdeps/unix/sysv/linux/alpha/bits/dirent.h
+++ b/sysdeps/unix/sysv/linux/alpha/bits/dirent.h
@@ -29,7 +29,7 @@ struct dirent
__off_t d_off;
unsigned short int d_reclen;
unsigned char d_type;
- char d_name[256]; /* We must not include limits.h! */
+ __flexarray (d_name, char, 256); /* We must not include limits.h! */
};
#ifdef __USE_LARGEFILE64
@@ -40,7 +40,7 @@ struct dirent64
__off64_t d_off;
unsigned short int d_reclen;
unsigned char d_type;
- char d_name[256]; /* We must not include limits.h! */
+ __flexarray (d_name, char, 256); /* We must not include limits.h! */
};
#endif
diff --git a/sysdeps/unix/sysv/linux/bits/dirent.h b/sysdeps/unix/sysv/linux/bits/dirent.h
index 31b1961..b7137e0 100644
--- a/sysdeps/unix/sysv/linux/bits/dirent.h
+++ b/sysdeps/unix/sysv/linux/bits/dirent.h
@@ -30,7 +30,7 @@ struct dirent
#endif
unsigned short int d_reclen;
unsigned char d_type;
- char d_name[256]; /* We must not include limits.h! */
+ __flexarray (d_name, char, 256); /* We must not include limits.h! */
};
#ifdef __USE_LARGEFILE64
@@ -40,7 +40,7 @@ struct dirent64
__off64_t d_off;
unsigned short int d_reclen;
unsigned char d_type;
- char d_name[256]; /* We must not include limits.h! */
+ __flexarray (d_name, char, 256); /* We must not include limits.h! */
};
#endif
