Update from Gnulib

This incorporates:
2019-02-24 nstrftime: support the ‘+’ flag
2019-02-24 stat, lstat: fix conflict with relocatable-prog-wrapper
2019-02-23 nstrftime: tweak arg order
2019-02-21 nstrftime: merge glibc strftime changes
2019-02-02 vla: add commentary about VLA_ELEMS
* build-aux/config.guess, doc/misc/texinfo.tex, lib/fstatat.c:
* lib/lstat.c, lib/nstrftime.c, lib/vla.h:
Copy from Gnulib.

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/vla.h b/lib/vla.h
index f6ebba0ede3..8f5dea76f61 100644
--- a/lib/vla.h
+++ b/lib/vla.h
@@ -17,6 +17,20 @@
 
    Written by Paul Eggert.  */
 
+/* The VLA_ELEMS macro does not allocate variable-length arrays (VLAs),
+   so it does not have the security or performance issues commonly
+   associated with VLAs.  VLA_ELEMS is for exploiting a C11 feature
+   where a function can start like this:
+
+     double scan_array (int n, double v[static n])
+
+   to require a caller to pass a vector V with at least N elements;
+   this allows better static checking and performance in some cases.
+   In C11 this feature means that V is a VLA, so the feature is
+   supported only if __STDC_NO_VLA__ is defined, and for compatibility
+   to platforms that do not support VLAs, VLA_ELEMS (n) expands to
+   nothing when __STDC_NO_VLA__ is not defined.  */
+
 /* A function's argument must point to an array with at least N elements.
    Example: 'int main (int argc, char *argv[VLA_ELEMS (argc)]);'.  */
 
@@ -25,3 +39,15 @@
 #else
 # define VLA_ELEMS(n) static n
 #endif
+
+/* Although C99 requires support for variable-length arrays (VLAs),
+   some C compilers never supported VLAs and VLAs are optional in C11.
+   VLAs are controversial because their allocation may be unintended
+   or awkward to support, and large VLAs might cause security or
+   performance problems.  GCC can diagnose the use of VLAs via the
+   -Wvla and -Wvla-larger-than warnings options, and defining the
+   macro GNULIB_NO_VLA disables the allocation of VLAs in Gnulib code.
+
+   The VLA_ELEMS macro is unaffected by GNULIB_NO_VLA, since it does
+   not allocate VLAs.  Programs that use VLA_ELEMS should be compiled
+   with 'gcc -Wvla-larger-than' instead of with 'gcc -Wvla'.  */