Cross-compiling and <dlfcn.h>

[Bossach]

I had some problems when cross-compiling PoCL (for another non-x86 linux system). There was some "implicit declaration" of "dlopen(), dlclose() .." and so on.

It is caused by not including <dlfcn.h> hided under #ifdef

For example:

/lib/CL/devices/devices.c:115
...
#ifdef HAVE_DLFCN_H
#if defined(__APPLE__)
#define _DARWIN_C_SOURCE
#endif
#include <dlfcn.h>
#endif
...

After some digging i found HAVE_DLFCN_H sets here under some conditions:

/CMakeLists.txt:964
...
if (CMAKE_CROSSCOMPILING AND (NOT ENABLE_HOST_CPU_DEVICES) AND (NOT ENABLE_HSA))
    message(STATUS "Cross-compiling without CPU/HSA devices -> skipping LIBDL search")
  else()
    ...
       set(HAVE_DLFCN_H ON CACHE BOOL "dlfcn.h" FORCE)
    ...
...

So temporary fix is build with -DENABLE_HOST_CPU_DEVICES=ON and it compiles and all works just fine.
But i don't need HOST_CPU_DEVICE neither HSA, just wanna build with my device driver only.

So the questions:

1. What the reason to hide finding and defining dlfcn under such condition?
   (if (CMAKE_CROSSCOMPILING AND (NOT ENABLE_HOST_CPU_DEVICES) AND (NOT ENABLE_HSA)))
   (I assume that may works just for me, but in other cases this condition may have sense)

2. How it intended to compile in case of not defined HAVE_DLFCN_H without including <dlfcn.h> despite that, for example, devices.c contains related function calls? (dlopen(), dlclose() and so on)

Thanks!

[franz]

Hello,

What the reason to hide finding and defining dlfcn under such condition?

The reason was to skip searching for dlfcn.h when it's not needed and might not work (e.g. cross-compiling for Android). Originally the only code using dlopen was in the CPU drivers and the HSA driver.

despite that, for example, devices.c contains related function calls

The code in devices.c that uses dlopen is ifdef'ed on ENABLE_LOADABLE_DRIVERS, the problem is that the CMake if command was not update to reflect this. If you compile without loadable drivers and without CPU/HSA then dlfcn should not be required at all.

[Bossach]

Thank you for your answer!

Indeed, i successfuly compiled it with just my device using -DENABLE_LOADABLE_DRIVERS=OFF, thanks for the tip.
(despite now something brokes at runtime (some xxxShedulerxxx symbol missing ), maybe it related to my custom device driver, will dig for it later)

So, as i understand, the updated "CMake if command" like if (CMAKE_CROSSCOMPILING AND (NOT ENABLE_HOST_CPU_DEVICES) AND (NOT ENABLE_HSA) AND (NOT ENABLE_LOADABLE_DRIVERS)) will be OK?
(and/or theoretically if( ... AND (NOT ENABLE_SOME_DL_USING_DRIVER)))
Did i understand correctly? (Or it's not OK because will break something else)

Thanks!

[franz]

Hi, sorry for late reply. Yeah updating the CMake line like that should be OK, probably ENABLE_PROXY_DEVICE also needs to be added into the if condition (it seems proxy driver includes dlfcn.h, but i haven't examined the code in detail).