llvm dev - Nov 2012 - [LLVMdev] Linking Clang with an optional external library

Hi,

I'd like to link Clang against the STP theorem prover. Since Clang is built
by the LLVM build system, I hope this is the correct place to ask for advice.

The attached patch allows me to pass `configure` a --with-stp option and provide
a path to the install prefix for STP. However, I am not familiar with autoconf,
so I am not confident that my changes are the correct way to do this. I would
appreciate feedback on the proposed change.

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Besides the configure.ac changes in the patch, I am unsure of the appropriate
place to add the linker flag. Currently I am simply appending to LDFLAGS in
Clang's tools/driver/Makefile:

+ifdef STP_INSTALL_PREFIX
+LDFLAGS += -L$(STP_INSTALL_PREFIX)/lib -lstp
+endif


To support CMake builds as well, is it sufficient to add the following to
config.h.cmake, and expect the user to pass -DWITH_STP_PREFIX= if they would
like to use this feature?

#cmakedefine STP_C_INTERFACE ${WITH_STP_PREFIX}/include/stp/c_interface.h


One potential issue I noticed in writing this patch is that LLVM's config.h
and Clang's config.h are both #include-guarded by the CONFIG_H macro, and
consequently both cannot be included from the same source file. Perhaps these
should be changed to LLVM_CONFIG_H and CLANG_CONFIG_H, respectively?


Thanks,
Ryan

Ryan Govostes <rzg at apple.com> writes:
> To support CMake builds as well, is it sufficient to add the following
> to config.h.cmake, and expect the user to pass -DWITH_STP_PREFIX= if
> they would like to use this feature?
>
> #cmakedefine STP_C_INTERFACE ${WITH_STP_PREFIX}/include/stp/c_interface.h
I see two problems with your approach:

* You force the user to always explicitly say where the library is
  located. On Unixy systems there are a set of well-known places where
  libraries are installed and most build systems (including the
  autotools and cmake) can fetch that library for you. The usual
  approach is to use a flag for requiring the library and an optional
  path for telling the build system where to look.

* As you mention, the part that adds the header location to the #include
  search list and the part that link the library are missing.

See r123976 (and the improvement on r128769) for an example of doing all
the above on CMake. That case is a bit more complicated than yours,
because it checks for the presence of the header file on two places and
allows independent locations for the header file and the library file,
when you only need the common prefix for both, but you can get the
idea. It also shows the required changes on config.h.cmake and the
CMakeFile(s) that adds the library to the compiler/linker invocation.
> One potential issue I noticed in writing this patch is that LLVM's
> config.h and Clang's config.h are both #include-guarded by the
> CONFIG_H macro, and consequently both cannot be included from the same
> source file. Perhaps these should be changed to LLVM_CONFIG_H and
> CLANG_CONFIG_H, respectively?
Strange indeed. CMake's build uses no guards at all on Clang's config.h
and it works fine. I wonder how the Clang config+make build works at
all. It seems that the part that source files that use the info on
Clang's config.h does not use LLVM at all, and vice-versa.

Hi Ryan,
> I'd like to link Clang against the STP theorem prover.
why?  If it's because you want to load a plugin that uses STP, why not link
the
plugin itself against STP?

Ciao, Duncan.

  Since Clang is built by the LLVM build system, I hope this is the correct 
place to ask for advice.
>
> The attached patch allows me to pass `configure` a --with-stp option and
provide a path to the install prefix for STP. However, I am not familiar with
autoconf, so I am not confident that my changes are the correct way to do this.
I would appreciate feedback on the proposed change.
>
>
>
>
>
> Besides the configure.ac changes in the patch, I am unsure of the
appropriate place to add the linker flag. Currently I am simply appending to
LDFLAGS in Clang's tools/driver/Makefile:
>
> +ifdef STP_INSTALL_PREFIX
> +LDFLAGS += -L$(STP_INSTALL_PREFIX)/lib -lstp
> +endif
>
>
> To support CMake builds as well, is it sufficient to add the following to
config.h.cmake, and expect the user to pass -DWITH_STP_PREFIX= if they would
like to use this feature?
>
> #cmakedefine STP_C_INTERFACE ${WITH_STP_PREFIX}/include/stp/c_interface.h
>
>
> One potential issue I noticed in writing this patch is that LLVM's
config.h and Clang's config.h are both #include-guarded by the CONFIG_H
macro, and consequently both cannot be included from the same source file.
Perhaps these should be changed to LLVM_CONFIG_H and CLANG_CONFIG_H,
respectively?
>
>
> Thanks,
> Ryan
>
>
>
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