I'm trying to wrap my head around how MT and MD options are used when compiling C/C++ projects. However, without being able to expand these supposed abbreviations to meaningful phrases, I forget which one is which from one paragraph to the next. Strangely enough none of the text I've read starts by defining the M, the T and the D. What do they stand for?
From the compiler options link given by chris above:
https://learn.microsoft.com/en-us/cpp/build/reference/compiler-options-listed-alphabetically?view=vs-2019
/MD Creates a multithreaded DLL using MSVCRT.lib.
/MDd Creates a debug multithreaded DLL using MSVCRTD.lib.
/MT Creates a multithreaded executable file using LIBCMT.lib.
/MTd Creates a debug multithreaded executable file using LIBCMTD.lib.
Thus MT stands for Multithreaded and MD stands for Multithreaded DLL.
These switches for cl.exe specify which C runtime library to link against; /MT specifies to link with LIBCMT.LIB; /MD specifies to link with MSVCRT.LIB.
The different CRT libraries are described in greater detail here. The primary difference between LIBCMT and MSVCRT is that the former links the CRT statically into your output file, whereas MSVCRT links to the VC runtime DLL (which, unlike its name suggests, is not MSVCRT.DLL (see here)).
DLL and internal may be used as mnemonic to distinguish /MD from /MT.
Related
When compiling my C and fortran code on Linux, I use the flag -nofor-main to specify that the main routine is not written in fortran. (See here for flag details)
How do I specify that the main routine is not written in Fortran if I am compiling on windows?
There is no need on Windows for an option to specify that the main is not Fortran. You may, however, want to consider the /libdir:noauto option (in Visual Studio, Fortran > Libraries > Disable Default Library Search Rules > Yes.) This prevents the Fortran compiler from adding linker directives that pull in Fortran language support libraries. You would then have to specify these when you link the main program.
Otherwise, be very sure that you select the same set of support libraries (DLL vs. static, debug vs. release) as you do in your non-Fortran project.
It appears I can just omit the specification and compilation remains successful.
I don't repeat more than necessary, brief summary:
Following the Adder example from this tutorial on a machine with win7 (64) with VS 2010.
But I don't use C++ but plain C.
When using the cl (MS compiler) with cl /Zi (and no other flag) it works like expected.
If not use /Zi and then try to execute the exe goes into flames.
Why?
(There must be some compiler/link options that make some init in the start of the haskell dll go wrong )
EDIT:
Some investigation:
/Zi does not affect optimizations. However, /Zi does imply /debug; see /DEBUG (Generate Debug Info) for more information.
/DEBUG changes the defaults for the /OPT option from REF to NOREF and from ICF to NOICF (so, you will need to explicitly specify /OPT:REF or /OPT:ICF).]
/OPT:ICF can result in the same address being assigned to different functions or read only data members (const variables compiled with /Gy). So, /OPT:ICF can break a program that depends on the address of functions or read-only data members being different. See /Gy (Enable Function-Level Linking) for more information.
Can someone confirm that /OPT:ICF will affect the loading of a Haskell/GHC compiled shared library(dll) ?
With g++ with -g option, I can use gdb for debugging purposes.
What's the equivalent to this option with Visual Studio 2010 cl.exe compiler?
This page has different libraries (debug/release) for linking.
If I compile with debugging option with cl.exe, do I have to use the corresponding library linking options (/MD/MT vs /MDd/MTd)?
There are a few separate pieces to this question: how to tell the compiler/linker to generate and preserve "debug information" (mapping between source code and object code), how to tell the compiler to compile the code differently to make debugging easier (think of assert() and #ifdef _DEBUG), and whether the precompiled libraries you link into your project include debugging information.
-Zi (flag to the CL compiler to tell it to generate debug information) is the equivalent of gcc's -g flag.
(There are other forms of the -Z option: -ZI if you want the "edit and continue" support in the Visual Studio IDE, but if you're using the IDE you're probably using its interface to the compiler settings instead of manipulating them directly, and -Z7 if you want the old CodeView-format debug information; whenever I've invoked CL directly it's always been -Zi that I wanted.)
Note that using the -Zi (or -ZI) option will generate a .pdb file per directory, usually, but when you link code together, it may have come from .obj files represented in different .pdb files, and you also want to combine those separate .pdb files into a master one representing the code you linked together -- this is what the -debug switch for the linker is for.
Also note: this may sound counterintuitive, but always use -Zi (for CL) and -debug (for link.exe). Even for code you're going to release. It doesn't increase the size of your executable, or give away secrets to your customers, since the debug information goes in a separate .pdb file (which you won't ship to customers). If there's any chance you're ever going to have to debug it, you're going to want the .pdb. (-Zi isn't even incompatible with optimizations, though -ZI is. So you might want to compile your "debug" builds with -ZI, and your "release" builds with "-Zi -O2".)
As for the libraries: you don't strictly need to match the debug/release property of the C runtime library with whether your code includes debugging information, but it's usually a good idea -- if you're going to debug the project you want to be able to debug all of it, and if you're not going to debug it you don't need the extra weight. Using debug/release versions of a given library won't affect whether it has debug symbols available (hopefully, if whoever compiled the library understood the point I made in the previous paragraph), but it will affect things like assert and extra #ifdef _DEBUG code in that library.
This goes for all libraries you link with, but especially for the C runtime library -- Microsoft added extra error-detection code to malloc() and free(). So if anything in your project is using the debug flavor of the CRT library, all of it should be.
The /M options (/MTd and /MDd) are weird and magic, in my opinion -- they're just aliases for a complicated set of other stuff going on behind the scenes. Take /MDd for example, documented to "Defines _DEBUG, _MT, and _DLL and causes your application to use the debug multithread- and DLL-specific version of the run-time library. It also causes the compiler to place the library name MSVCRTD.lib into the .obj file." Here, it's affecting both the preprocessor (defining _DEBUG and some other preprocessor symbols) and the linker (it actually puts a #pragma comment(linker) in your source code). If you care about what's going on and don't understand it, this can cause real problems -- I've seen a lot of projects that don't use the IDE get bogged down in warnings about both msvcrt.lib and msvcrtd.lib being linked in, etc. By the time you understand how to use these (/M options) safely, you don't really need them any more! I prefer to make things explicit: specify "-D _DEBUG" directly where I need it, specify which libraries to link with explicitly (and use -nodefaultlib), and then the /M options aren't needed.
You're looking for one of the debug information generation options (/Z7, /Zi or /ZI).
If you use one of those, you should also pass the /DEBUG option to the linker.
You will also need to link against the debug version of the runtime libraries (/MDd or /MTd). This is important because these versions are different from their release counterparts (e.g. their memory allocations routines are not compatible).
When developing and deploying native Windows applications, I often need to install a runtime before being able to run my binary, or statically link the library with my binary. For instance, after building a "Win32 Console" project with Visual Studio 2008, attempting to run the program on a fresh Windows 7 image results in:
The application has failed to start because its side-by-side configuration is incorrect. Please see the application event log or use the command-line sxstrace.exe tool for more detail.
Issues like this one have been brought up in other posts on StackOverflow.
How does one develop applications that don't require runtimes that aren't already on the target OS (i.e. don't require installing redistributable packages or private/shared side-by-side assemblies)? How does one avoid using msvc[mpr]90.dll and just use the Windows API in \windows\system32*.{dll,sys}?
I'm thinking along the lines of the code that comes out of the demoscene, but that's frequently not made available.
Others have already responded with respect to linking CRT statically. If you also want a small binary at the same time, then your best bet is forego CRT entirely, and use only Win32 API functions as much as possible. You'll still get some CRT code, most notably related to startup (i.e. that which calls main) and shutdown (atexit handling etc), but otherwise the linker won't link CRT functions that you do not use.
You can avoid linking CRT altogether by using /Zl compiler switch. This means that main will no longer work, however - you'll need to define WinMain (name doesn't matter, but signature must match, and it must be __stdcall), and you will have to specify the name of your WinMain-like function as an entry point via linker /entry: switch. This will save you ~30Kb of CRT code (tested on a .cpp with an empty main).
If you go the latter route, you might also have to deal with issue of compiler intrinsics. There are some functions that are nominally defined by the CRT (and declared in its headers), but which are treated specially by the compiler, so that it inserts optimized assembly instructions at the point of the call where possible - examples are memset, strlen, and a good chunk of functions in <math.h>; a complete list can be found here. Since you don't have CRT, if you need these functions, or could avoid it but prefer the intrinsic because of improved performance (hard to do better than memset, for example), then you have to declare them yourself, and use #pragma intrinsic. E.g.:
// Contains macros and typedef only, so safe to include without CRT.
// We need it here for size_t.
#include <stddef.h>
extern "C"
{
int abs(int);
void* memset(void*, int, size_t);
}
#pragma intrinsic(abs, memset)
int __stdcall main(void*, void*, char*, int)
{
char tmp[10];
memset(tmp, abs(-123), 10);
return 0;
}
The above can be compiled with:
cl /c /Zl foo.cpp
link /entry:main foo.obj
Link the CRT statically via the /MT switch (and likewise MFC, if you're using it).
Static linking limits what you can do with DLLs somewhat, but for simple executables it works like a charm. (And if you're shipping DLLs, you can always ship private assemblies anyway.)
Use the static CRT. This doesn't create a dependency on msvc*.dll. The CRT is linked directly into your program. This doesn't create dependencies, but does increase the size of your executable.
More info on different CRT options here.
Statically link the runtime. MS Visual C++ has option /MT for that (default is /MD)
I think one way to do this is to just not use Visual Studio and instead rely on the command line SDK tools. (You can alternatively figure out how to config VS to do what you want, but that seems harder.) E.g.:
cl /c app.cpp
link app.obj ws2_32.lib
Which headers should I not use if I don't want my program to be linked with any of msvc*.dll ?
At the moment my application uses:
kernel32
user32
shell32
msvcp90
msvcr90
I want to get rid of the bottom two files. I don't mind if I will have to rewrite certain aspects of the program.
Because I know if you code in C and then link it won't link any msvc's
I believe you have to change the way the CRT is linked into your program. I think for that you have to change the C++->Code Generation->Runtime-Library to the static version. This is for Visual Studio 2005, don't know about newer versions.
Those libraries contain the C++ runtime - heap management and other stuff hard to get rid from.
You could link the C++ statically instead - use "C++ -> Code Generation -> Runtime Library" setting. Then you will not need those .dll files. However this is not the recommended way - if a vulnerability is found in the C++ runtime you'll have to recompile and reship your program.
Static link is the right answer. A related bit of advice is to use depends.exe to see what functions your exe is actually hitting in the dependent dlls. Those dependencies might be due to explicit use on your part or due to CRT implementation that you don't explicitly invoke.