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Document 32-bit time_t problem on minw-w64 toolchain and how to avoid it

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Paul Graham 2017-02-15 23:04:04 +01:00
parent 9d75e5ea97
commit b2b47a7d11
2 changed files with 29 additions and 1 deletions
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22
README.windows
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@ -12,7 +12,8 @@ cross compilers on Windows.
To configure and build LibreSSL for a 32-bit system, use the following
build steps:
CC=i686-w64-mingw32-gcc ./configure --host=i686-w64-mingw32
CC=i686-w64-mingw32-gcc CPPFLAGS=-D__MINGW_USE_VC2005_COMPAT \
./configure --host=i686-w64-mingw32
make
make check
@ -22,6 +23,25 @@ For 64-bit builds, use these instead:
make
make check
# Why the -D__MINGW_USE_VC2005_COMPAT flag on 32-bit systems?
An ABI change introduced with Microsoft Visual C++ 2005 (also known as
Visual C++ 8.0) switched time_t from 32-bit to 64-bit. It is important to
build LibreSSL with 64-bit time_t whenever possible, because 32-bit time_t
is unable to represent times past 2038 (this is commonly known as the
Y2K38 problem).
If LibreSSL is built with 32-bit time_t, when verifying a certificate whose
expiry date is set past 19 January 2038, it will be unable to tell if the
certificate has expired or not, and thus take the safe stance and reject it.
In order to avoid this, you need to build LibreSSL (and everything that links
with it) with the -D__MINGW_USE_VC2005_COMPAT flag. This tells mingw-w64 to
use the new ABI.
64-bit systems always have a 64-bit time_t and are not affected by this
problem.
# Using Libressl with Visual Studio
A script for generating ready-to-use .DLL and static .LIB files is included in

8
configure.ac
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@ -142,6 +142,14 @@ AM_CONDITIONAL([SMALL_TIME_T], [test "$ac_cv_sizeof_time_t" = "4"])
if test "$ac_cv_sizeof_time_t" = "4"; then
echo " ** Warning, this system is unable to represent times past 2038"
echo " ** It will behave incorrectly when handling valid RFC5280 dates"
if test "$host_os" = "mingw32" ; then
echo " **"
echo " ** You can solve this by adjusting the build flags in your"
echo " ** mingw-w64 toolchain. Refer to README.windows for details."
fi
exit 1
fi
AC_REQUIRE_AUX_FILE([tap-driver.sh])