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CURL_STATIC_CRT no longer works with cmake 3.15 and above #5165

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CURL_STATIC_CRT no longer works with cmake 3.15 and above#5165
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cmake

Description

@rogerorr
rogerorr
opened on Mar 30, 2020

Building curl with -DCURL_STATIC_CRT=ON

Run "x64 Native Tools Command Prompt for VS 2019"
> git clone https://github.com/curl/curl
(on commit 69d5d18)
> md build
> cd build

> cmake -DCURL_STATIC_CRT=ON -DBUILD_SHARED_LIBS=OFF ../curl
> cmake --build . --target curl

I see the following

> dumpbin /imports src\Debug\curl.exe | find ".dll"
WLDAP32.dll
WS2_32.dll
ADVAPI32.dll
KERNEL32.dll
VCRUNTIME140D.dll
ucrtbased.dll

(This is identical with the output when -DCURL_STATIC_CRT=ON is not provided)

I expected the following

> dumpbin /imports src\Debug\curl.exe | find ".dll"
WLDAP32.dll
WS2_32.dll
ADVAPI32.dll
KERNEL32.dll

curl/libcurl version

> src\Debug\curl.exe -V
curl 7.70.0-DEV (Windows) libcurl/7.70.0-DEV
Release-Date: [unreleased]
Protocols: dict file ftp gopher http imap ldap pop3 rtsp smb smtp telnet tftp
Features: AsynchDNS IPv6 Largefile NTLM

operating system

Windows 10 1909

I am using Visual Studio 16.5.1, and the cmake that is supplied with VS (cmake version 3.16.19112601-MSVC_2)

Analysis

Cmake CMP0091 ( https://cmake.org/cmake/help/git-stage/policy/CMP0091.html ) changes the way CMake on Windows handles the flags controlling the C runtime being used.

Prior to CMake 3.15 the /MT or /MTd flags could simply be added to CMAKE_C_FLAGS_DEBUG or CMAKE_C_FLAGS_RELEASE.
Starting with CMake 3.15 the CMAKE_MSVC_RUNTIME_LIBRARY abstraction should be used instead -- values provided in the other locations are ignored.

Possible Solution

Change CMakeLists.txt:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e70a6e348..a410d4955 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -232,6 +232,7 @@ set(CMAKE_C_FLAGS "${CMAKE_ANSI_CFLAGS} ${CMAKE_C_FLAGS}")
 set(CMAKE_REQUIRED_FLAGS ${CMAKE_ANSI_CFLAGS})

 if(CURL_STATIC_CRT)
+  set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
   set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} /MT")
   set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} /MTd")
 endif()

Note: the existing settings should be left in place, for versions of cmake prior to 3.15

Activity

  1. bagder
    added
    cmake
    on Mar 30, 2020

  2. bagder commented on Mar 30, 2020

    @bagder
    bagder
    on Mar 30, 2020
    Member

    Seems primarily like a cmake bug to me... Should CMAKE_MSVC_RUNTIME_LIBRARY really be set independent of what platform/compiler that's used? Can you please provide your suggested fix as a pull request?

  3. rogerorr
    added a commit that references this issue on Mar 30, 2020

    Add CMAKE_MSVC_RUNTIME_LIBRARY: fixes curl#5165

    03688e0
  4. bagder
    linked a pull request that will close this issueAdd CMAKE_MSVC_RUNTIME_LIBRARY: fixes #5165 #5167on Mar 30, 2020

  5. rogerorr commented on Mar 30, 2020

    @rogerorr
    rogerorr
    on Mar 30, 2020
    ContributorAuthor

    I agree with you that it is a cmake issue - but I think this is mostly because they're trying to improve the vexing issue of handling the Microsoft compiler's setting of the relevant options controlling the C/C++ runtime library.

    The existing code handling CURL_STATIC_CRT in curl's CMakeLists.txt is already WIN32 specific, and the additional flags /MT and /MTd are Microsoft specific, so I think adding the CMAKE_MSVC_RUNTIME_LIBRARY setting here is appropriate.

    P/R #5167 raised

  6. jzakrzewski commented on Mar 30, 2020

    @jzakrzewski
    jzakrzewski
    on Mar 30, 2020
    Contributor

    The behaviour is controlled by cmake policy CMP0091, which is automatically set to NEW if your top project declares minimum version of cmake to 3.15+. It must have been #4975 that introduced the problem for curl.

    If I understand the description of CMAKE_MSVC_RUNTIME_LIBRARY correctly, cmake will only apply it where it makes sense, so it can be set without thinking about other platforms/compilers, etc.

  7. rogerorr commented on Mar 30, 2020

    @rogerorr
    rogerorr
    on Mar 30, 2020
    ContributorAuthor

    That matches my understanding.

  8. bagder
    closed this as completedin 6d65a19on Mar 30, 2020
  9. jonhoo
    added 2 commits that reference this issue on Jul 22, 2026

    fix: build Windows C++ core with a static CRT

    113525c

    fix: build Windows C++ core with a static CRT (#15)

    0bc9399
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