By default, Newlib uses a huge object of type struct _reent to store
thread-specific data. This object is returned by __getreent() if the
__DYNAMIC_REENT__ Newlib configuration option is defined.
The reentrancy structure contains for example errno and the standard input,
output, and error file streams. This means that if an application only uses
errno it has a dependency on the file stream support even if it does not use
it. This is an issue for lower end targets and applications which need to
qualify the software according to safety standards (for example ECSS-E-ST-40C,
ECSS-Q-ST-80C, IEC 61508, ISO 26262, DO-178, DO-330, DO-333).
If the new _REENT_THREAD_LOCAL configuration option is enabled, then struct
_reent is replaced by dedicated thread-local objects for each struct _reent
member. The thread-local objects are defined in translation units which use
the corresponding object.
The _REENT_GLOBAL_STDIO_STREAMS was introduced by commit
668a4c8722 in 2017. Since then it was enabled by
default for RTEMS. Recently, the option was enabled for Cygwin which
previously used an alternative implementation to use global stdio streams.
In Newlib, the stdio streams are defined to thread-specific pointers
_reent::_stdin, _reent::_stdout and _reent::_stderr. If the option is disabled
(the default for most systems), then these pointers are initialized to
thread-specific FILE objects which use file descriptors 0, 1, and 2,
respectively. There are at least three problems with this:
(1) The thread-specific FILE objects are closed by _reclaim_reent(). This
leads to problems with language run-time libraries that provide wrappers to
the C/POSIX stdio streams (for example C++ and Ada), since they use the
thread-specific FILE objects of the initialization thread. In case the
initialization thread is deleted, then they use freed memory.
(2) Since thread-specific FILE objects are used with a common output device via
file descriptors 0, 1 and 2, the locking at FILE object level cannot ensure
atomicity of the output, e.g. a call to printf().
(3) There are resource managment issues, see:
https://sourceware.org/pipermail/newlib/2022/019558.htmlhttps://bugs.linaro.org/show_bug.cgi?id=5841
This patch enables the _REENT_GLOBAL_STDIO_STREAMS behaviour for all Newlib
configurations and removes the option. This removes a couple of #ifdef blocks.
Remove the pointer indirection through the read-only _global_impure_ptr and
directly use a externally visible _impure_data object of type struct _reent.
This enables the static initialization of global data structures in a follow up
patch. In addition, we get rid of a machine-specific file.
* libc/reent/impure.c (reent_data): Define as alias to impure_data
when building for Cygwin.
* libc/include/sys/reent.h (_GLOBAL_REENT): Revert definition to
_global_impure_ptr.
* libc/include/sys/_types.h: Include <sys/lock.h> and change
_flock_t to be of type _LOCK_RECURSIVE_T.
* libc/include/sys/reent.h: (_REENT_INIT): Reformat.
(_REENT_INIT_PTR): Ditto. Use memset where appropriate.
(_global_impure_ptr): New declaration.
(_GLOBAL_REENT): Change to be _global_impure_ptr.
* libc/include/sys/stdio.h: Include <sys/lock.h> and
<sys/reent.h>.
(_flockfile)[!_SINGLE_THREAD]: Add code for lock call.
(_funlockfile)[!SINGLE_THREAD]: Ditto.
* libc/reent/impure.c: Set _global_impure_ptr to _impure_ptr.
* libc/stdio/fclose.c: Remove casting of fp lock to
_LOCK_RECURSIVE_T.
* libc/stdio/findfp.c: Ditto.
* libc/stdio/fopen.c: Ditto.
* libc/stdio/freopen.c: Ditto.
* libc/stdio/vfprintf.c: Ditto.
* libc/stdio64/fopen64.c: Ditto.
* libc/stdlib/envlock.c: Add default stubs that use generic
locking code.
* libc/stdlib/mlock.c: Ditto.
Jeff Johnston <jjohnstn@redhat.com>
* libc/sys/linux/sys/_types.h (__flock_mutex_t): New subtype.
(_flock_t): Change to be a struct containing a single member
named mutex which is of type __flock_mutex_t.
Matt Joyce
Sebastian Huber
Yaakov Selkowitz
Jeff Johnston
Christopher Faylor