LD_PRELOAD is a list of additional ELF shared objects that should be loaded first.
LD_PRELOAD is a list of additional ELF shared objects that should be loaded first.
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Questions tagged [ld-preload]
265 questions
7
votes
2 answers
How can I intercept dlsym calls using LD_PRELOAD?
I want to intercept application's calls to dlsym. I have tried declaring inside the .so that I am preloading dlsym , and using dlsym itself to get it's real address, but that for quite obvious reasons didn't work.
Is there a way easier than taking…
user1588911
- 71
- 1
- 3
6
votes
1 answer
intercepting the openat() system call for GNU tar
I'm trying to intercept the openat() system call on Linux using a custom shared library that I can load via LD_PRELOAD. An example intercept-openat.c has this content:
#define _GNU_SOURCE
#include
#include
#include…
Julius Plenz
- 63
- 1
- 3
6
votes
1 answer
How to use perf with ld_preload?
I tried to use perf stat with LD_PRELOAD as prefix for executable such as:
perf stat LD_PRELOAD=$PWD/../user/preload.so ./write 1
It seems not work for perf, are there any way to achieve it?
Steven
- 811
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- 23
6
votes
3 answers
How to wrap variadic functions using LD_PRELOAD?
I have to perform dynamic linking on a variadic function of following format:
int foo(char *args, const char *f, ...)
Here the number of arguments are variable.
What I want to achieve is that I want to pass the obtained arguments to the original…
ankit jain
- 350
- 2
- 12
6
votes
2 answers
Using LD_PRELOAD mixed 64bit/32bit environment in Linux
I would like to set LD_PRELOAD to point to a shared library where I might run either a 64bit or 32bit application. It is obvious that the shared library and the executable have to match in bit-ness.
$ LD_PRELOAD=/lib64/lib_init.so…
Robert McLay
- 63
- 1
- 3
6
votes
2 answers
How to wrap ioctl(int d, unsigned long request, ...) using LD_PRELOAD?
Here's the template I use for wrapping a function using LD_PRELOAD:
int gettimeofday(struct timeval *tv, struct timezone *tz) {
static int (*gettimeofday_real)(struct timeval *tv, struct timezone *tz)=NULL;
if (!gettimeofday_real)…
d33tah
- 10,999
- 13
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- 158
6
votes
1 answer
LD_PRELOAD causing segmentation fault in dynamic library loader
I have written a library which is intended to be loaded via LD_PRELOAD. On some Linux systems, this is causing the dynamic library loader to segfault during initialisation.
I have a simple test case that exhibits this behaviour, but only if I link…
jprice
- 9,755
- 1
- 28
- 32
6
votes
2 answers
Replacing the close() function in Linux with my own close() function
I'm trying to provide my own implementation of the close() function in Linux. Why? Because I just found out you could do that and it sounds fun.
Here's myclose.c:
#include
int close(int fd) {
printf("Closing fd: %d\n", fd);
return…
gsgx
- 12,020
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- 149
6
votes
1 answer
What are the differences between LD_PRELOAD and strace?
Both methods are used to gather system calls also parameters and return values of them. When we prefer LD_PRELOAD and why? Maybe we can say that we can only gather syscalls via strace but we can gather library calls with LD_PRELOAD trick. However,…
Ricardo Cristian Ramirez
- 1,194
- 3
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- 42
5
votes
2 answers
How to debug functions in a dynamic library loaded with LD_PRELOAD with gdb?
I'm trying to debug some functions in a dynamic shared library libexecHook.so. This library is preloaded setting LD_PRELOAD in order to intercept and rewrite some calls to execve() and friends. For debugging purposes I have built gmake with symbols.…
Marko
- 128
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- 9
5
votes
1 answer
Why doesn't LD_PRELOAD take effect with scripts having no shebang?
If, when I run a script, I use LD_PRELOAD to designate a library to preload, I find that the library is in fact preloaded only if the script has a shebang line. For example, given this script:
# Not a shebang
echo Hello
and this…
John Bollinger
- 160,171
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- 157
5
votes
2 answers
why doesn't LD_PRELOAD trick catch open() when called by fopen()?
I use the LD_PRELOAD trick to catch open64() calls and I think I know how to do it correctly: with the program foobar compiled from
#include
#include
#include
int main() {
open64("foobar.txt", 0);
return…
Mark Galeck
- 6,155
- 1
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- 55
5
votes
5 answers
How to override assert macro in C?
I want to create my own version of assert in which it does some log prints in case assert was called in NDEBUG mode.
I tried to do the LD_PRELOAD trick and redefine the assert macro but it seems to ignore the macro definition completely and…
itayb
- 139
- 3
- 10
5
votes
1 answer
Presenting a virtual filesystem to a Linux process without root access
I'm looking for a way to present a userspace filesystem to a specific Linux process but I don't have root access.
The obvious answer is FUSE but without root access I cannot load the kernel module and so FUSE seems to be out of the question (unless…
tommyvn
- 713
- 5
- 12
5
votes
3 answers
LD_PRELOADed libraries and child process
everyone!
Image that i have a program(usemalloc) like this:
#include
#include
#define USER_BYTES_SIZE 100
int main(void){
char* userbytes = (char*)malloc(USER_BYTES_SIZE*sizeof(char));
if(!userbytes)
return…
振 禹
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- 3