Pushed to trunk.
libstdc++-v3/ChangeLog:
* acinclude.m4 (GLIBCXX_ENABLE_FULLY_DYNAMIC_STRING): Improve
comments.
* configure: Regenerate.
---
libstdc++-v3/acinclude.m4 | 17 +++++++++++------
libstdc++-v3/configure | 4 ++--
2 files changed, 13 insertions(+), 8 deletions(-)
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 336c690f07b..930861e6a94 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -499,19 +499,24 @@ AC_DEFUN([GLIBCXX_CHECK_LFS], [
dnl
-dnl Check for whether a fully dynamic basic_string implementation should
-dnl be turned on, that does not put empty objects in per-process static
-dnl memory (mostly useful together with shared memory allocators, see PR
-dnl libstdc++/16612 for details).
+dnl Check whether the old Copy-On-Write basic_string should allocate a new
+dnl empty representation for every default-constructed basic_string. Without
+dnl this option, COW strings share a single empty rep in static storage,
+dnl but this only works if the linker can guarantee the static storage has
+dnl a unique definition in the process. It also doesn't work if basic_string
+dnl objects are stored in shared memory (see PR libstdc++/16612).
+dnl When fully dynamic strings are enabled, the static storage is not used
+dnl and a new empty string with reference-count == 1 is allocated each time.
+dnl Enabling this changes the libstdc++.so ABI.
dnl
dnl --enable-fully-dynamic-string defines _GLIBCXX_FULLY_DYNAMIC_STRING to 1
dnl --disable-fully-dynamic-string defines _GLIBCXX_FULLY_DYNAMIC_STRING to 0
-dnl otherwise undefined
+dnl otherwise the macro is not defined.
dnl + Usage: GLIBCXX_ENABLE_FULLY_DYNAMIC_STRING[(DEFAULT)]
dnl Where DEFAULT is either `yes' or `no'.
dnl
AC_DEFUN([GLIBCXX_ENABLE_FULLY_DYNAMIC_STRING], [
- GLIBCXX_ENABLE(fully-dynamic-string,$1,,[do not put empty strings in
per-process static memory])
+ GLIBCXX_ENABLE(fully-dynamic-string,$1,,[do not put empty strings in
per-process static memory], [permit yes|no])
if test $enable_fully_dynamic_string = yes; then
enable_fully_dynamic_string_def=1
else
