mheffner

$ make libab.so
gcc -Wall -fPIC -fvisibility=hidden   -c -o filea.o filea.c
gcc -Wall -fPIC -fvisibility=hidden   -c -o fileb.o fileb.c
gcc -Wall -fPIC -fvisibility=hidden -shared -o libab.so filea.o fileb.o

$ strip --strip-all --discard-all libab.so 

$ objdump -T libab.so  | grep get
Exit 1

mheffner

$ strip --strip-all --discard-all libab.so 

$ objdump -t libab.so           

libab.so:     file format elf64-x86-64

SYMBOL TABLE:
no symbols

mheffner

$ make
gcc -Wall -fPIC   -c -o test.o test.c
gcc -Wall -fPIC   -c -o filea.o filea.c
gcc -Wall -fPIC   -c -o fileb.o fileb.c
gcc -shared -o libab.so filea.o fileb.o
gcc -o test test.o -L. -lab

$ objdump -t libab.so | grep get
00000000000005dc l     F .text  000000000000000b              a_internal_getval
0000000000000634 l     F .text  000000000000000b              b_internal_getval

mheffner

/* fileb.c */

/* Internal to this file. */
static int
b_internal_getval(void)
{

	return 4;
}

mheffner

/* filea.c */
#include <stdio.h>

/* Include public API definitions. */
#include "ab.h"

/* Function provided by fileb.c */
int b_getval_super_secret(void);

/* Simple function internal to this file only. */

mheffner

/* ab.h -- External API for libab. */
#ifndef __AB_H__
#define  __AB_H__

const char *ab_get_string(void);

#endif /* ! __AB_H__ */

mheffner

$ gcc -g3 -Wall -fPIC -shared -o condwait_wrap.so condwait_wrap.c -ldl -lpthread -Wl,--version-script -Wl,VERSION.txt

$ LD_PRELOAD=./condwait_wrap.so ./condwait_test
Calling condwait v. 2.3.2 with cond: 0x600d80, mutex: 0x600dc0.....got it!
Thread exiting

$ objdump -t condwait_wrap.so | grep pthread_cond_wait
000000000000074a l     F .text	000000000000006c              pthread_cond_wait_225
00000000000007b6 l     F .text	000000000000006c              pthread_cond_wait_232
00000000000007b6 g     F .text	000000000000006c              pthread_cond_wait@@GLIBC_2.3.2

mheffner

GLIBC_2.2.5 {
        global:
                pthread_cond_wait;
        local:
                *;
};

GLIBC_2.3.2 {
        global:
                pthread_cond_wait;

mheffner

$ gcc -g3 -Wall -fPIC -shared -o condwait_wrap.so condwait_wrap.c -ldl -lpthread
/usr/bin/ld: condwait_wrap.so: version node not found for symbol pthread_cond_wait@@GLIBC_2.3.2
/usr/bin/ld: failed to set dynamic section sizes: Bad value
collect2: ld returned 1 exit status
Exit 1

mheffner

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <pthread.h>

static int (*condwait_internal_225)(pthread_cond_t *cond,
				    pthread_mutex_t *mutex);

static int (*condwait_internal_232)(pthread_cond_t *cond,