Re: Problem with dlopen and shared objects using perl libs

AFAICT, there are two problems:

the output of `perl -MExtUtils::Embed -e ccopts -e ldopts` (in particular the -lperl therein) is inserted too early on the command line. As the linker (ld) by default only searches once to satisfy externally referenced symbols, the perl library didn't get included.
when you load the shared lib using dlopen, you need to specify RTLD_GLOBAL (instead of RTLD_LOCAL), so the symbols will be made visible to any subsequently loaded libs, such as Data/Dumper/Dumper.so.

Here's how I got it to work on my Linux box (with Perl installed under /usr/local/perl/5.10.0):

# compile/link shared lib which includes Perl interpreter:

gcc -Wall -pedantic -fPIC -shared \
    -o perl_test1.so  perl_test1.c \
    `/usr/local/perl/5.10.0/bin/perl -MExtUtils::Embed -e ccopts -e ld
+opts`

# compile/link the test program that loads it using dlopen:

gcc -Wall -pedantic -Wl,-rpath=. \
    -o perl_test2  perl_test2.c \
    -ldl

# ...and run it:

$ ./perl_test2
$VAR1 = 'this is a string';
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Re^2: Problem with dlopen and shared objects using perl libs by swehack (Novice) on Mar 11, 2008 at 08:15 UTC
Thank you very much for your help almut. I can't believe it was as simple as gcc arguments being in the wrong order, it now compiles and runs fine on my FreeBSD to. I guess that's what i get from not fully understanding my compiler and linker. I knew about the RTLD_GLOBAL though from listposts but i first and foremost wanted to find out what i did wrong with the linking.	[reply]
Re^2: Problem with dlopen and shared objects using perl libs by swehack (Novice) on Mar 14, 2008 at 20:08 UTC
Hi again, perhaps you can help me with this new problem i have related to the last. I'm stuck because even if the program i wrote as an example compiles fine, the real module for my project does not and i believe it's because PERL_NO_SHORT_NAMES is not defined or respected in my project while it is in the example program. I can make no sense at all of this because in my example program, i have Perl_doing_taint even if i remove the `#define PERL_NO_SHORT_NAMES` directive. While it always uses the short names in my project, what is causing this? I've tried modifying the arguments i use to compile so many times and the way i see it the main differences are that in my project i have -lircbot which links all my modules to a library with some common functions for them to use. Besides that i bring in the ccopts and ldopts in a configure script which strips the newline and puts it all into a variable so it looks like this: `PERL_OPTS= -Wl,-R/usr/local/lib/perl5/5.8.8/mach/CORE -Wl,-E -L/usr/local/lib /usr/local/lib/perl5/5.8.8/mach/auto/DynaLoader/DynaLoader.a -L/usr/local/lib/perl5/5.8.8/mach/CORE -lperl -lm -lcrypt -lutil -DAPPLLIB_EXP="/usr/local/lib/perl5/5.8.8/BSDPAN" -DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -I/usr/local/lib/perl5/5.8.8/mach/CORE` but i've also tried just using `perl -MExtUtils::Embed -e ccopts -e ldopts` directly in the Makefile rule and it didn't help. So the way i see it, the only difference in the arguments is `-Isrc -I.. -L../.. -lircbot` which must be included in the arguments for my projects modules. How could this possibly cause PERL_NO_SHORT_NAMES to be ignored?! And how on earth is it defined in the example program even if i remove the preprocessing directives defining it and refuse to define it on the command line? I even tried compiling and linking the example program with -lircbot like my projects module is, it didn't affect the fact that nm returned the symbol Perl_doing_taint still, even though i nowhere define PERL_NO_SHORT_NAMES anymore. I must note that i can actually compile my example program module without the `#define PERL_NO_SHORT_NAMES` and when i check it's symbols with `nm perl_test1.so \| grep taint` i see that it's not using short names, i see Perl_doing_taint. But when i check the symbols on my module i see doing_taint so i must assume that getting my module to respect PERL_NO_SHORT_NAMES will solve my problem because right now the program exits with this message: `/libexec/ld-elf.so.1: modules/peval.so: Undefined symbol "doing_taint"` [download] Things like this just boggles my mind. Here is the Makefile i use along with the primary Makefile that defines ccopts and ldopts. Makefile: SHELL=/bin/sh CC=gcc LD=ld LDFLAGS+=-rpath . -L. CFLAGS+=-g -Wall -pedantic -ansi -DSETPROCTITLE -DPERL_NO_SHORT_NAMES LIBS+=-lircbot INCLUDES+=-Isrc -I.. HEADERS=bicebot.h ircbot.h PERL_OPTS= -Wl,-R/usr/local/lib/perl5/5.8.8/mach/CORE -Wl,-E -L/usr/ +local/lib /usr/local/lib/perl5/5.8.8/mach/auto/DynaLoader/DynaLoader. +a -L/usr/local/lib/perl5/5.8.8/mach/CORE -lperl -lm -lcrypt -lutil -D +APPLLIB_EXP="/usr/local/lib/perl5/5.8.8/BSDPAN" -DHAS_FPSETMASK -DHAS +_FLOATINGPOINT_H -fno-strict-aliasing -pipe -Wdeclaration-after-state +ment -I/usr/local/include -I/usr/local/lib/perl5/5.8.8/mach/CORE SRC=src SRC_MODS:=$(SRC)/mods # TODO: some sort of PREFIX to install elsewhere # also install target MODULES=modules export all: $(MAKE) -f $(SRC)/Makefile $(MAKE) -C $(SRC_MODS) @echo 'All done, now run bicebot.' modules: $(MAKE) -C $(SRC_MODS) # TODO: so you can rebuild only modules clean-modules: rm -f $(MODULES)/.so $(SRC_MODS)/.o clean: rm -f .o bicebot .so $(MODULES)/.so $(SRC_MODS)/.o [download] src/mods/Makefile MODS_SRCS=$(wildcard *.c) MODS_OBJS=$(MODS_SRCS:%.c=%.o) MODS_TRGT=$(MODS_OBJS:%.o=%.so) LDFLAGS+=-L../.. all: $(MODS_TRGT) #gcc -Wall -fPIC -shared -o perl_test1.so perl_test1.c `perl -MExtUtil +s::Embed -e ccopts -e ldopts` $(MODS_TRGT): $(MODS_SRCS) $(CC) -Wall -Isrc -I.. -rpath . -L. -L../.. -fPIC -shared -o ../.. +/$(MODULES)/$@ $(@:%.so=%.c) `perl -MExtUtils::Embed -e ccopts -e ldo +pts` -lircbot -lc [download] I've been trying and testing tons of different methods in the last Makefile so excuse the mess but maybe you can figure out why it acts like this if i show you how i compile and link the module.	[reply] [d/l] [select]