Re: static linking libssl and libcrypto

[Aijaz Baig <aijazbaig1@xxxxxxxxx>]

Thank you for the information.

I will address your points here:

1. I was not aware of the fact that only those symbols that have been used get imported when linking a library statically. So that very well could be the case. I didn't get what you mentioned about the static linking preventing the program from requiring libSSL.so. I mean the way I am linking my library should be of no concern to the source code right? Or so I think.

2. when I downloaded and compiled the openssl library (from source), I followed the INSTALL read me. All it resulted was libssl.a and libcrypto.a. I didn't find any file name libSSL.so. So how will this static library (archive) have references to libSSL.so on the system?? I am kind of confused here now.

Keen to hear from you,

Aijaz

On Mon, Nov 4, 2019 at 4:59 PM Brice André <brice@xxxxxxxxxxxxxxxx> wrote:

Hello,

It's not an open-ssl issue, but more a compiler specific one.

With info you provided, I cannot tell you what you get as results, but two points that may help:

1. regarding the 87 ssl symbols : when you link with a library, only the useful symbols are imported. So, if the code in you libAPP library only uses some sparse functions of libSSL, it's normal you only have corresponding symbols in your final image. I don't know what you plan to do, but note that statically linking your dll with open-ssl will prevent this dll from needing the openssl dynamic library. But it will not prevent your main program to require the open-ssl library to run properly if some part of it is dynamically linked with open-ssl !
   
2. depending on how you compiled your libssl.a, it can be either a static library containing the full openssl binary code, or a static library that just makes the "link" between you code and the ssl dynamic library. In the second case, even if you properly statically link with this lib, you will still need the dll to execute your program.

Regards,

Brice

Le lun. 4 nov. 2019 à 07:28, Aijaz Baig <aijazbaig1@xxxxxxxxx> a écrit :

I am trying to build a shared library that internally links openssl and crypto libraries statically so I can use it in a production environment. To that end I am using the following Makefile

APPBASE=/home/AB/Documents/APP/APP_2.17.0
OPENSSL1.0.2p_INSTALL_LOC=/home/AB/Documents/APP/OpenSSL-1.0.2p-installation
CC=gcc
CFLAGS= -Wall -g -O -fPIC
RM= rm -f
.PHONY: all clean

src="" *Generic/*.c *Linux/*.c)
$(info source=$(src))

#we use the custom compiled openssl version
#and NOT the one available on the system
#INC=-I/usr/include/openssl
INC+=-I$(OPENSSL1.0.2p_INSTALL_LOC)/include/openssl
INC+=$(foreach d,$(incdir),-I$d)
$(info includes=$(INC))

LIB=-L$(OPENSSL1.0.2p_INSTALL_LOC)/lib
#LIB=-llibssl -llibcrypto
LIB+=-lssl -lcrypto
$(info links=$(LIB))
#LIB+=-L/usr/lib/

obj=$(src:.c=.o)
all: libAPP.so
clean:
    $(RM) *.o *.so
    $(shell find $(APPBASE) -type f -iname "*.o" -exec rm -rf {} \;)

.c.o:
    ${CC} -static ${CFLAGS} $(INC) -c $< $(LIB) -o $@

libAPP.so: $(obj)
    $(LINK.c) -shared $^ -o $@

As mentioned here (https://stackoverflow.com/questions/18185618/how-to-use-static-linking-with-openssl-in-c-c/25811538#25811538), I've changed the linker flags to:

-lcrypto -lz -ldl -static-libgcc




but it doesn't seem to change the size of the generated so file. On checking for references to SSL in this so file, I see there are a total of 87 entries




nm libAPP.so | grep -i "ssl" | wc -l

87




whereas listing only the global symbols from libssl.a tells me it has 1113 globally defined symbols.

nm -g ../OpenSSL-1.0.2p-installation/lib/libssl.a | grep -i "ssl" | wc -l


1113




I do not know if libSSL got indeed linked statically or not. Could someone please shed some light on it?





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Best Regards,

Aijaz Baig

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Best Regards,

Aijaz Baig