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Build: Conditionally allow win95 threads and --enable-small.

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When the compiler supports __attribute__((__constructor__))
mythread_once() is never used, even with --enable-small. A configuration
with win95 threads and --enable-small will compile and be thread safe so
it can be allowed.

This isn't a very common configuration since MSVC does not support
__attribute__((__constructor__)), but MINGW32 and CLANG32 environments
for MSYS2 can use win95 threads and have
__attribute__((__constructor__)) support.
This commit is contained in:
Jia Tan 2023-08-09 20:35:16 +08:00
parent 6bf33b704c
commit de574404c4
1 changed files with 13 additions and 8 deletions
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21
configure.ac
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@ -437,14 +437,6 @@ case $enable_threads in
;;
esac
# The Win95 threading lacks thread-safe one-time initialization function.
# It's better to disallow it instead of allowing threaded but thread-unsafe
# build.
if test "x$enable_small$enable_threads" = xyeswin95; then
AC_MSG_ERROR([--enable-threads=win95 and --enable-small cannot be
used at the same time])
fi
# We use the actual result a little later.
@ -861,6 +853,19 @@ AC_COMPILE_IFELSE([
])
CFLAGS="$OLD_CFLAGS"
# The Win95 threading lacks a thread-safe one-time initialization function.
# The one-time initialization is needed for crc32_small.c and crc64_small.c
# create the CRC tables. So if small mode is enabled, the threading mode is
# win95, and the compiler does not support attribute constructor, then we
# would end up with a multithreaded build that is thread-unsafe. As a
# result this configuration is not allowed.
if test "x$enable_small$enable_threads$have_func_attribute_constructor"\
= xyeswin95no; then
AC_MSG_ERROR([--enable-threads=win95 and --enable-small cannot be
used at the same time with a compiler that doesn't support
__attribute__((__constructor__))])
fi
# __attribute__((__ifunc__())) can be used to choose between different
# implementations of the same function at runtime. This is slightly more
# efficient than using __attribute__((__constructor__)) and setting