dependencies in .so files

[guido@sirio.stat.unipd.it]

 Thomas Lumley writes:
 > 
 > 
 > I've been trying to get Matt Calder's S compiler to work in R using R
 > COMPILE and R SHLIB so it will be fairly platform-independent.  
 > 
 > I'm sure someone has claimed in the past that it is possible/easy to
 > dyn.load() two dynamic libraries and have one call functions in the other.
 > I can't get it to work (Red Hat 5.0/R0.61.1ish). It doesn't seem to matter
 > what order I load them in, they can't find each other.
 > 
 > Any ideas?
 
 >From the dlopen man page:
 void *dlopen (const char *filename, int flag);
 ................................................
 RTLD_GLOBAL may be or'ed with flag
 in which case the external symbols defined in the library will be
 made available to subsequently loaded libraries.
 
 So, I try: 
 1) I modify src/unix/dynload.c changing the flag of dlopen
    from RTLD_LAZY to (RTLD_LAZY | RTLD_GLOBAL)
 2) build two simple shared libraries the second calling a routine 
    in the first.
 ---------------------------a.c-------------------------------
 #include <stdio.h>
 
 void a(int *i) {
    printf("now in a.so; incrementing i\n");
    *i=*i+1;
 }
 
 --------------------------b.c--------------------------------
 #include <stdio.h>
 
 extern void a(int *i);
 
 void b(int *i) {
    printf("in b.so; calling function a in a.so; i=%d\n",*i);
    a(i);
    printf("in b.so; now i=%d\n",*i);
 }
 
 -------------------------Makefile------------------------------
 all: a.so b.so
 
 a.o: a.c
 	gcc -fPIC -c a.c
 	
 a.so: a.o
 	gcc -shared -o a.so a.o
 	
 b.o: b.c
 	gcc -fPIC -c b.c
 	
 b.so: b.o
 	gcc -shared -o b.so b.o	
 	
 -------------------------------------------------------------------------
 
 Things seems ok.
 
 -------------------------------------------------------------------------
 sirio[~/tmp/prova]% R
 
 R : Copyright 1998, Robert Gentleman and Ross Ihaka
 Version 0.61.3  (May 3, 1998)
 
 R is free software and comes with ABSOLUTELY NO WARRANTY.
 You are welcome to redistribute it under certain conditions.
 Type    "license()" for details.
 
 Type    "demo()" for some demos, "help()" for on-line help, or
         "help.start()" for a HTML browser interface to help.
 
 
 > dyn.load("a.so")
 > dyn.load("b.so")
 > y <- .C("b",as.integer(0))
 in b.so; calling function a in a.so; i=0
 now in a.so; incrementing i
 in b.so; now i=1
 > y
 [[1]]
 [1] 1           
 ----------------------------------------------------------------------------
 
 Before introducing the RTLD_GLOBAL flag:
 ----------------------------------------------------------------------------
 sirio[~/tmp/prova]% R
 
 R : Copyright 1998, Robert Gentleman and Ross Ihaka
 Version 0.61.3  (May 3, 1998)
 
 R is free software and comes with ABSOLUTELY NO WARRANTY.
 You are welcome to redistribute it under certain conditions.
 Type    "license()" for details.
 
 Type    "demo()" for some demos, "help()" for on-line help, or
         "help.start()" for a HTML browser interface to help.
 
 > dyn.load("a.so")
 > dyn.load("b.so")
 > y <- .C("b",as.integer(0))
 in b.so; calling function a in a.so; i=0
 /usr/local/src/R-0.61.3/bin/R.binary: can't resolve symbol 'a'
 sirio[~/tmp/prova]%                                             
 
 ----------------------------------------------------------------------------
 I am using R-0.61.3 under Linux 2.30.
 
 guido masarotto
 

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