header error in static build on windows

[tihmstar]

There is an issue with LIMD_GLUE_API definition in installed headers, which prevents static builds on windows.

In case of a static build, LIMD_GLUE_STATIC is defined in configure.ac

libimobiledevice-glue/configure.ac

Line 132 in 0779631

GLOBAL_CFLAGS+=" -DLIMD_GLUE_STATIC"

and passed to the environment as a compiler flag.

In the source files it is checked here:

libimobiledevice-glue/include/libimobiledevice-glue/glue.h

Lines 25 to 33 in 0779631

	#ifndef LIMD_GLUE_API
	#ifdef LIMD_GLUE_STATIC
	#define LIMD_GLUE_API
	#elif defined(_WIN32)
	#define LIMD_GLUE_API __declspec(dllimport)
	#else
	#define LIMD_GLUE_API
	#endif
	#endif

To decide how LIMD_GLUE_API should be defined if it doesn't already exist.

The problem however is, that LIMD_GLUE_STATIC is never defined outside of the buildenvironment of libimobiledevice-glue itself!
Which means that this case:

libimobiledevice-glue/include/libimobiledevice-glue/glue.h

Lines 26 to 28 in 0779631

	#ifdef LIMD_GLUE_STATIC
	#define LIMD_GLUE_API
	#elif defined(_WIN32)

Is never true when a 3rd party imports libimobiledevice-glue headers. As a result, on windows the headers will always define

libimobiledevice-glue/include/libimobiledevice-glue/glue.h

Line 29 in 0779631

#define LIMD_GLUE_API __declspec(dllimport)

which causes linker errors down the line when libimobiledevice-glue was built statically.

---

Checking whether libimobiledevice-glue was built statically cannot be done this way.
One solution would be to pre-process the header and statically resolve the condition before installing the header.

One example of this can be seen here:
https://github.com/tihmstar/img4tool/blob/d082f71dbf06f5d325140c14b47a0a214908f57c/include/img4tool/img4tool.hpp.in#L19-L21

Note: This problem also applies to other libimobiledevice projects which define _APIs in a similar matter.

[nikias]

Well, you just need to define it when you want to link statically. Other projects do it similarly, e.g. if you are linking libcurl statically, you also have to define CURL_STATICLIB. Moreover, if you build static AND dynamic libs, how would you decide what to put in the headers?

[tihmstar]

Think of this usecase:
I want to for example build idevicerestore fully static on windows.
So i download the following projects libplist, libimobiledevice-glue, libusbmuxd,libirecovery, libimobiledevice and finally idevicerestore.

I go to each project and run ./autogen.sh --enable-static --disable-shared, make, make install.
By the time i reach libirecovery or libimobiledevice (where the binaries are compiled), i get hit with linker errors.

Defining all of them ahead of time via export LIMD_GLUE_STATIC=1 would probably work in theory, but if i'm required to do that anyways, why is LIMD_GLUE_STATIC defined inside the buildsystem then? That seems redundant and (to me as a user) confusing, since i would assume the buildsystem takes care of it.

Though, i would suggest to omit __declspec(dllimport) altogether. I don't have it in any of my projects and it still links fine dynamically. Since the buildsystem assumes either cygwin or mingw anyways, it mean the compiler will use gcc or clang (you could even require those). Those can do the linking correctly without __declspec(dllimport). Export definition is still needed, but not the import one.