Re: Gcc 5.4 Compilation failure with -fPIC: undefined reference to `getrpcbynumber'

[Matt <mattator at gmail dot com>]

> I thinking you are missing the point here: glibc already provides
> both the shared and library and static library for static case.
Indeed great ! Thanks for the help.

I work on a project called DCE
(https://www.nsnam.org/docs/dce/release/1.8/manual/html/intro.html),
whose goal is to allow to run real software such as iperf/ip/ping
within the Network Simulation tool "ns3". To do so, DCE creates a
*fake* libc that overrides some of the calls and keep the native libc
function otherwise. It loads one *fake* libc per application, and the
applications are run within a single process (it's a complex program
IMO).

The project does so in a somewhat hackish manner (using wrapper
functions towards functoin pointers in a struct that is filled later
on when it's loaded by the simulator etc...) and I wanted to explore
alternatives such as static linking the libc calls that are not
overriden, aka the native calls.
I've written a small file libc.c:
==
extern int printf(const char*, ...);
int toto()
{
    printf("holy libc");
}
==

My idea is to have the original printf glibc code linked in my own
version of libc.so:
$ gcc -nostdlib -fPIC libc.c  -L/home/teto/glibc/f -lc_pic -shared -o mylibc.so

which returns:
/usr/bin/ld.bfd.real: libc.so: version node not found for symbol
pthread_cond_wait@@GLIBC_2.3.2
/usr/bin/ld.bfd.real: failed to set dynamic section sizes: Bad value

I don't understand why "pthread_cond_wait" would be  needed at all ? I
thought that static linking would only copy the required (printf) code
and its dependancies in mylibc.so
Maybe I should compile libc with libpthread as an addon:
https://www.gnu.org/software/hurd/open_issues/libpthread_addon.html

Feel free to ignore this question if you deem it too *newbish* but
having some pointers/help would be great, I am a bit new to linking
concepts.

Cheers
Matt

2016-07-21 22:17 GMT+02:00 Adhemerval Zanella <adhemerval.zanella@linaro.org>:
>
>
> On 21/07/2016 15:40, Matt wrote:
>> Hi,
>>
>> I've been trying various branches (master branch, 2.23 tag) and
>> various configurations in order to compile libc on ubuntu 16.04 with
>> gcc-5.real (Ubuntu 5.4.0-6ubuntu1~16.04.1) 5.4.0 20160609 with -fPIC
>> (I want to create a shared library statically linking some glibc
>> functions.
>
> I thinking you are missing the point here: glibc already provides
> both the shared and library and static library for static case.  Also
> static linking a shared library with a libc.a is problematic in a sense
> libc maintains some internal states that might be interfered with the
> libc shared library.
>
> Why exactly do you need the libc functions on the shared library? Why
> can't you just statically link libc against the program itself?
>
>>
>> I came up with this command:
>> $ CFLAGS=" -fPIC  -O2 -fno-stack-protector -U_FORTIFY_SOURCE "
>> LD_LIBRARY_PATH="" ../configure --prefix=/home/teto/libcinstall
>> --disable-shared --enable-static-nss --enable-obsolete-rpc
>> --disable-werror
>>
>> but I keep ending up with:
>> ===
>> make[2]: Entering directory '/home/teto/glibc/nss'
>> gcc -nostdlib -nostartfiles -static -o /home/teto/glibc/d/nss/getent
>>  /home/teto/glibc/d/csu/crt1.o /home/teto/glibc/d/csu/crti.o `gcc
>> --print-file-name=crtbeginT.o` /home/teto/glibc/d/nss/getent.o
>> -Wl,--start-group /home/teto/glibc/d/libc.a -lgcc -lgcc_eh
>> -Wl,--end-group `gcc  --print-file-name=crtend.o`
>> /home/teto/glibc/d/csu/crtn.o
>> /home/teto/glibc/d/nss/getent.o: In function `rpc_keys':
>> getent.c:(.text+0xc37): undefined reference to `getrpcbynumber'
>> getent.c:(.text+0xc64): undefined reference to `getrpcbyname'
>> getent.c:(.text+0xc93): undefined reference to `setrpcent'
>> getent.c:(.text+0xca9): undefined reference to `getrpcent'
>> getent.c:(.text+0xcb3): undefined reference to `endrpcent'
>> collect2: error: ld returned 1 exit status
>> ../Rules:147: recipe for target '/home/teto/glibc/d/nss/getent' failed
>> make[2]: *** [/home/teto/glibc/d/nss/getent] Error 1
>> ====
>> is there anything I can do to fix this ?
>> also if I don't compile first with a simpler command, "libc-modules.h"
>> doesn't get created, thus stopping the compilation process :/
>>
>> Best regards
>>