[glib/glib-2-46] gnulib: %n is not supported on old glibc or on native win32

[Ignacio Casal Quinteiro <icq src gnome org>]

commit 94688bc12c0c41c96ff0124e426614ebda4313ec
Author: Ignacio Casal Quinteiro <icq gnome org>
Date:   Mon Oct 12 09:20:36 2015 +0200

    gnulib: %n is not supported on old glibc or on native win32
    
    On old glibc even if %n is supported we may get a crash, so it is
    better to skip it while on native win32 %n will abort the program.
    These changes were took from upstream.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=756382

 glib/gnulib/vasnprintf.c |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+), 0 deletions(-)
---
diff --git a/glib/gnulib/vasnprintf.c b/glib/gnulib/vasnprintf.c
index 018e0d9..69c0b91 100644
--- a/glib/gnulib/vasnprintf.c
+++ b/glib/gnulib/vasnprintf.c
@@ -699,9 +699,36 @@ vasnprintf (char *resultbuf, size_t *lengthp, const char *format, va_list args)
                  }
                *p = dp->conversion;
 #if HAVE_SNPRINTF
+# if !(((__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3)) && !defined __UCLIBC__) || ((defined 
_WIN32 || defined __WIN32__) && ! defined __CYGWIN__))
                p[1] = '%';
                p[2] = 'n';
                p[3] = '\0';
+# else
+               /* On glibc2 systems from glibc >= 2.3 - probably also older
+                * ones - we know that snprintf's returns value conforms to
+                * ISO C 99: the gl_SNPRINTF_DIRECTIVE_N test passes.
+                * Therefore we can avoid using %n in this situation.
+                * On glibc2 systems from 2004-10-18 or newer, the use of %n
+                * in format strings in writable memory may crash the program
+                * (if compiled with _FORTIFY_SOURCE=2), so we should avoid it
+                * in this situation.  */
+               /* On native Win32 systems (such as mingw), we can avoid using
+                * %n because:
+                *   - Although the gl_SNPRINTF_TRUNCATION_C99 test fails,
+                *     snprintf does not write more than the specified number
+                *     of bytes. (snprintf (buf, 3, "%d %d", 4567, 89) writes
+                *     '4', '5', '6' into buf, not '4', '5', '\0'.)
+                *   - Although the gl_SNPRINTF_RETVAL_C99 test fails, snprintf
+                *     allows us to recognize the case of an insufficient
+                *     buffer size: it returns -1 in this case.
+                * On native Win32 systems (such as mingw) where the OS is
+                * Windows Vista, the use of %n in format strings by default
+                * crashes the program. See
+                * <http://gcc.gnu.org/ml/gcc/2007-06/msg00122.html> and
+                * <http://msdn2.microsoft.com/en-us/library/ms175782(VS.80).aspx>
+                * So we should avoid %n in this situation.  */
+               p[1] = '\0';
+# endif
 #else
                p[1] = '\0';
 #endif