On 07/12/20 12:36 -0800, Keith Packard wrote:
Jonathan Wakely <jwak...@redhat.com> writes:
GCC changelog files are autogenerated now, so patches should not touch
them. Just include the ChangeLog entry in the Git commit log (which
will usually end up being quoted in the patch and/or the email body of
the mail to gcc-patches).
Awesome.
I think the right way to do this (or at least, the way that was
intended when basic_file_stdio.cc was added) is to provide a new file
and change GLIBCXX_ENABLE_CSTDIO in acinclude.m4 to use that new file.
The two biggest downsides of that are that it duplicates a lot of the
file (because the diffs for your changes are small) and that the
correct name for your new file is already taken!
I can definitely see a reason to use a separate file when implementing
the basic_file interface on top of something other than stdio, but
this patch doesn't do that -- it only changes the interaction between
basic_file and stdio in a few places.
I think it makes the best long-term sense to leave everything in
basic_file_stdio.cc and avoid having the two implementations diverge in
the future.
However, it's rather late in the GCC 11 process to make a change like
that (even though it's really just renaming some files). Would you be
OK waiting until after GCC 11 is released (in 4-5 months) to do it
"properly"? Is this blocking something that would require doing it
sooner?
This patch enables the use of C++ with picolibc, a libc designed for 32-
and 64- bit embedded systems.
Right now, I'm working on getting picolibc support integrated into
Zephyr, which uses toolchains build by crosstool-ng. I've gotten
picolibc support merged to crosstool-ng, but the Zephyr developers are
interested in having a single toolchain support three different libc
implementations (newlib, newlib-nano and picolibc), but that's blocked
on having C++ support available in all three libraries.
So, you're at the bottom of my current dependency graph :-)
I don't particularly need this released in gcc, but I would like to
get patches reviewed and the general approach agreed on so that I can
feel more confident in preparing patches to be applied to gcc in
crosstool-ng itself.
Once that's done, I'll also be able to release new Debian packages of
GCC for embedded ARM and RISC-V and have those include suitable patches
so that we can support embedded C++ development there too.
OK. In principle, changes to avoid using the POSIX APIs are definitely
fine. I would like to combine your new configure switch with the
existing --enable-cstdio one though.
How about the attached change for acinclude.m4 which would allow you
to do --enable-cstdio=stdio_pure? (It also adds "stdio_posix" as a
more accurate alternative spelling of the current "stdio" option.)
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index fcd9ea3d23a..535ffd8682f 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -2862,24 +2862,30 @@ AC_DEFUN([GLIBCXX_ENABLE_PARALLEL], [
dnl
-dnl Check for which I/O library to use: stdio, or something specific.
+dnl Check for which I/O library to use: stdio and POSIX, or pure stdio.
dnl
-dnl Default is stdio.
+dnl Default is stdio_posix.
dnl
AC_DEFUN([GLIBCXX_ENABLE_CSTDIO], [
AC_MSG_CHECKING([for underlying I/O to use])
GLIBCXX_ENABLE(cstdio,stdio,[[[=PACKAGE]]],
- [use target-specific I/O package], [permit stdio])
+ [use target-specific I/O package], [permit stdio|stdio_posix|stdio_pure])
- # Now that libio has been removed, you can have any color you want as long
- # as it's black. This is one big no-op until other packages are added, but
- # showing the framework never hurts.
+ # The only available I/O model is based on stdio, via basic_file_stdio.
+ # The default "stdio" is actually "stdio + POSIX" because it uses fdopen(3)
+ # to get a file descriptor and then uses read(3) and write(3) with it.
+ # The "stdio_pure" model doesn't use fdopen and only uses FILE* for I/O.
case ${enable_cstdio} in
- stdio)
+ stdio*)
CSTDIO_H=config/io/c_io_stdio.h
BASIC_FILE_H=config/io/basic_file_stdio.h
BASIC_FILE_CC=config/io/basic_file_stdio.cc
AC_MSG_RESULT(stdio)
+
+ if test "x$enable_cstdio" = "xstdio_pure" ; then
+ AC_DEFINE(_GLIBCXX_USE_PURE_STDIO, 1,
+ [Define to restrict std::__basic_file<> to stdio APIs.])
+ fi
;;
esac
