Re: [Mingw-w64-public] gcc parameter -mcrtdll= for choosing Windows C RunTime DLL library

["Pali Rohár" <pali.rohar@gmail.com>]

On Monday 21 November 2022 13:21:53 LIU Hao wrote:
> 在 2022/11/20 23:06, Pali Rohár 写道:
> > Thank you for explaining more details. My simple patch takes this in
> > care and defines also __MSVCRT_VERSION__ to the correct value based on
> > -mcrtdll parameter.
> 
> Apologies for reading your message only partially. I thought your patch was
> the same as MSYS2's. It turns out that you have made further progress;
> that's very kind of you.
> 
> As for the patch itself: It's probably safe to switch between MSVCR* DLLs,
> but switching from MSVCR* to UCRT requires a complete rebuild due to
> differences in implementation of stdio functions and definition of `time_t`
> on x86. There are more reasons, for example, that MSVCR80 and 90 require
> architecture-specific manifests to load, and MSVCR80 to 120 are not
> pre-installed and have to be installed by users. These could explain why
> `-mcrtdll=` hasn't gained wide use, while UCRT-based toolchains have.
> 
> So, the patch may be acceptable, but I don't think it will solve the issue
> for you. A user should usually choose MSVCRT or UCRT, which however requires
> rebuilding the CRT. For those who really really wish to link against
> MSVCR100 for example, it's always doable to pass `-nodefaultlibs` to GCC,
> and specify desired libraries explicitly.

The ultimate goal could be to improve mingw-w64 build process to compile
one set of libraries which would work with both msvcrt and ucrt. There
is already discussion about it in separate mingw-w64 email thread.
Probably not easy task, but I think it can be possible. Anyway, in any
case, this work is independent of gcc and independent of introduction of
-mcrtdll= gcc switch. So I think this switch still can be useful.