Allow locking routine to be retargeted

At the moment when targeting bare-metal targets or systems without
definition for the locking primitives newlib, uses dummy empty macros.
This has the advantage of reduced size and faster implementation but
does not allow the application to retarget the locking routines.
Retargeting is useful for a single toolchain to support multiple systems
since then it's only at link time that you know which system you are
targeting.

This patch adds a new configure option
--enable-newlib-retargetable-locking to use dummy empty functions
instead of dummy empty macros. The default is to keep the current
behavior to not have any size or speed impact on targets not interested
in this feature. To allow for any size of lock, the _LOCK_T type is
changed into pointer to struct _lock and the _init function are tasked
with allocating the locks. The platform being targeted must provide the
static locks. A dummy implementation of the locking routines and static
lock is provided for single-threaded applications to link successfully
out of the box.

To ensure that the behavior is consistent (either no locking whatsoever
or working locking), the dummy implementation is strongly defined such
that a partial retargeting will cause a doubly defined link error.
Indeed, the linker will only pull in the file providing the dummy
implementation if it cannot find an implementation for one of the
routine or lock.

1 files changed, 15 insertions, 0 deletions

diff --git a/newlib/configure.in b/newlib/configure.in
index bfaf038..354c07c 100644
--- a/newlib/configure.in
+++ b/newlib/configure.in
@@ -218,6 +218,17 @@ AC_ARG_ENABLE(newlib_nano_formatted_io,
    *) AC_MSG_ERROR(bad value ${enableval} for newlib-nano-formatted-io) ;;
  esac],[newlib_nano_formatted_io=no])
 
+dnl Support --enable-retargetable-locking
+dnl This option is also read in libc/configure.in.  It is repeated
+dnl here so that it shows up in the help text.
+AC_ARG_ENABLE(newlib-retargetable-locking,
+[  --enable-newlib-retargetable-locking    Allow locking routines to be retargeted at link time],
+[case "${enableval}" in
+   yes) newlib_retargetable_locking=yes ;;
+   no)  newlib_retargetable_locking=no ;;
+   *) AC_MSG_ERROR(bad value ${enableval} for newlib-retargetable-locking) ;;
+ esac],[newlib_retargetable_locking=no])
+
 NEWLIB_CONFIGURE(.)
 
 dnl We have to enable libtool after NEWLIB_CONFIGURE because if we try and
@@ -458,6 +469,10 @@ if test "${newlib_nano_formatted_io}" = "yes"; then
 AC_DEFINE_UNQUOTED(_NANO_FORMATTED_IO)
 fi
 
+if test "${newlib_retargetable_locking}" = "yes"; then
+AC_DEFINE_UNQUOTED(_RETARGETABLE_LOCKING)
+fi
+
 dnl
 dnl Parse --enable-newlib-iconv-encodings option argument
 dnl