Re: gcc parameter -mcrtdll= for choosing Windows C RunTime DLL library

["Pali Rohár" <pali.rohar@gmail.com>]

On Sunday 20 November 2022 13:53:48 Pali Rohár wrote:
> Hello! I would like to propose a new parameter for gcc: -mcrtdll= to
> allow specifying against which Windows C Runtime library should be
> binary linked. On Windows there are more crt libraries and currently gcc
> links to libmsvcrt.a which is in most cases symlink to libmsvcrt-os.a
> (but can be changed, e.g. during mingw-w64 building). mingw-w64 project
> already builds import .a library for every crt dll library (from the old
> crtdll.dll up to the new ucrtbase.dll), so it is ready for usage. Simple
> patch for gcc which implements -mcrtdll parameter is below. Note that on
> internet are other very similar patches for -mcrtdll= parameters and
> some are parts of custom mingw32 / mingw-w64 gcc builds. What do you
> think? Could gcc have "official" support for -mcrtdll= parameter?

Hello! I would like to ask gcc people, what do you think about such
proposed -mcrtdll= parameter?

There are lot of unofficial gcc patches which implement this -mcrtdll=
parameter and this parameter is present in more gcc forks.
So it looks like that this parameter is useful for more people.

Here is list of some URLs which I found:
https://sourceforge.net/p/mingw/mailman/message/5692227/
https://sourceforge.net/p/mingw-w64/mailman/message/36030107/
https://github.com/jmeubank/tdm-gcc-src/blob/tdm-patches.public/_PATCHES/mcrtdll.patch
https://github.com/msys2/MINGW-packages/blob/master/mingw-w64-gcc/0006-Windows-New-feature-to-allow-overriding.patch
https://github.com/nak5124/build_env/blob/master/gcc_build/patches/gcc/0020-MinGW-w64-Define-__MSVCRT_VERSION__.patch

But I have not found any discussion about it on gcc mailing list.

> 
> --- gcc/config/i386/cygming.opt	2022-02-06 21:00:05.377656896 +0100
> +++ gcc/config/i386/cygming.opt	2022-02-06 21:04:06.690995944 +0100
> @@ -22,6 +22,10 @@ mconsole
>  Target RejectNegative
>  Create console application.
>  
> +mcrtdll=
> +Target RejectNegative Joined
> +Link with specified C RunTime DLL library.
> +
>  mdll
>  Target RejectNegative
>  Generate code for a DLL.
> --- gcc/config/i386/mingw32.h	2022-01-16 17:28:31.157999097 +0100
> +++ gcc/config/i386/mingw32.h	2022-01-16 17:36:03.552856726 +0100
> @@ -95,7 +95,20 @@ along with GCC; see the file COPYING3.
>  #undef CPP_SPEC
>  #define CPP_SPEC "%{posix:-D_POSIX_SOURCE} %{mthreads:-D_MT} " \
>  		 "%{" SPEC_PTHREAD1 ":-D_REENTRANT} " \
> -		 "%{" SPEC_PTHREAD2 ": } "
> +		 "%{" SPEC_PTHREAD2 ": } " \
> +		 "%{mcrtdll=crtdll*:-U__MSVCRT__ -D__CRTDLL__} " \
> +		 "%{mcrtdll=msvcrt10*:-D__MSVCRT_VERSION__=0x100} " \
> +		 "%{mcrtdll=msvcrt20*:-D__MSVCRT_VERSION__=0x200} " \
> +		 "%{mcrtdll=msvcrt40*:-D__MSVCRT_VERSION__=0x400} " \
> +		 "%{mcrtdll=msvcrt-os*:-D__MSVCRT_VERSION__=0x700} " \
> +		 "%{mcrtdll=msvcr70*:-D__MSVCRT_VERSION__=0x700} " \
> +		 "%{mcrtdll=msvcr71*:-D__MSVCRT_VERSION__=0x701} " \
> +		 "%{mcrtdll=msvcr80*:-D__MSVCRT_VERSION__=0x800} " \
> +		 "%{mcrtdll=msvcr90*:-D__MSVCRT_VERSION__=0x900} " \
> +		 "%{mcrtdll=msvcr100*:-D__MSVCRT_VERSION__=0xA00} " \
> +		 "%{mcrtdll=msvcr110*:-D__MSVCRT_VERSION__=0xB00} " \
> +		 "%{mcrtdll=msvcr120*:-D__MSVCRT_VERSION__=0xC00} " \
> +		 "%{mcrtdll=ucrt*:-D_UCRT} "
>  
>  /* For Windows applications, include more libraries, but always include
>     kernel32.  */
> @@ -185,11 +198,16 @@ along with GCC; see the file COPYING3.
>  #define REAL_LIBGCC_SPEC \
>    "%{mthreads:-lmingwthrd} -lmingw32 \
>     " SHARED_LIBGCC_SPEC " \
> -   -lmoldname -lmingwex -lmsvcrt -lkernel32"
> +   -lmoldname -lmingwex %{!mcrtdll=*:-lmsvcrt} %{mcrtdll=*:-l%*} -lkernel32"
>  
>  #undef STARTFILE_SPEC
> -#define STARTFILE_SPEC "%{shared|mdll:dllcrt2%O%s} \
> -  %{!shared:%{!mdll:crt2%O%s}} %{pg:gcrt2%O%s} \
> +#define STARTFILE_SPEC " \
> +  %{shared|mdll:%{mcrtdll=crtdll*:dllcrt1%O%s}} \
> +  %{shared|mdll:%{!mcrtdll=crtdll*:dllcrt2%O%s}} \
> +  %{!shared:%{!mdll:%{mcrtdll=crtdll*:crt1%O%s}}} \
> +  %{!shared:%{!mdll:%{!mcrtdll=crtdll*:crt2%O%s}}} \
> +  %{pg:%{mcrtdll=crtdll*:gcrt1%O%s}} \
> +  %{pg:%{!mcrtdll=crtdll*:gcrt2%O%s}} \
>    crtbegin.o%s \
>    %{fvtable-verify=none:%s; \
>      fvtable-verify=preinit:vtv_start.o%s; \
>