I hope you don't mind my seeking on expertise here in C library linking. I've exhausted my search-fu and this is the place people know me. I hope my question is low level and generic enough that what I learn could be useful later working on opensmalltalk-vm.
PDFium is a component of Chromium/Chrome for rendering PDFS. By default it only builds a static library, but I found a configuration option to builds shared library, but it seems it misses some symbols. Now the object file remain available and I found the required symbol exported from them. For example...
$ nm -A fpdfview.o | grep FPDF_Init
fpdfview.o:0000000000000000 T FPDF_InitLibrary
fpdfview.o:0000000000000000 T FPDF_InitLibraryWithConfig
fpdfview.o:0000000000000000 t FPDF_InitLibraryWithConfig.part.47
IIUC, the capital "T" means the "FPDF_InitLibrary" symbol is exported and available for another program to link against. Browsing the web, it seems like object files can be composed into a shared library like this...
$ gcc -fPIC -shared -o libmypdf.so fpdfview.o
but I end up with the "FPDF_InitLibrary" hidden as an internal symbol...
$ nm -A libmypdf.so | grep FPDF_Init
libmypdf.so:0000000000003e60 t FPDF_InitLibrary
libmypdf.so:0000000000003e80 t FPDF_InitLibraryWithConfig
libmypdf.so:00000000000031f0 t FPDF_InitLibraryWithConfig.part.47
so I can't link my test code against it
Here is my makefile...
INC_DIR= -I ./public
LIB_DIR= -L ./out
STD_LIBS= -lpthread -lm -lc -lstdc++
PDF_LIBS= -lmypdfium
default:
gcc -o test test.c ${INC_DIR} ${LIB_DIR} ${PDF_LIBS} ${STD_LIBS}
Now I know the library is found, since if I change its name the linker complains it can't find the file.
I don't think the following adds useful extra info, but for completeness... The header file fpdfview.h has...
#if defined(_WIN32) && defined(FPDFSDK_EXPORTS)
// On Windows system, functions are exported in a DLL
#define FPDF_EXPORT __declspec(dllexport)
#define FPDF_CALLCONV __stdcall
#else
#define FPDF_EXPORT
#define FPDF_CALLCONV
#endif
#ifdef __cplusplus
extern "C" {
#endif
FPDF_EXPORT void FPDF_CALLCONV FPDF_InitLibrary();
#ifdef __cplusplus
}
#endif