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]
234 questions
26
votes
3 answers
LD_PRELOAD does not work as expected
Consider the following library which can be preloaded before any program execution:
// g++ -std=c++11 -shared -fPIC preload.cpp -o preload.so
// LD_PRELOAD=./preload.so
#include
struct Goodbye {
Goodbye() {std::cout <<…
Martin
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18
votes
1 answer
What is the exact equivalent to LD_PRELOAD on OSX?
I am using LD_PRELOAD to hook a library function, and in Linux it works perfectly. But I cannot figure out how to do the equivalent in OSX.
The setup I have on Linux is as follows:
The code is:
#include
#include
#include…
horseyguy
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16
votes
1 answer
link a static library to a shared library and hide exported symbols
I am having an annoying problem with the linker. I want to link some symbols from a shared library to a static library, but not export its symbols (ie, I cannot simply merge the libraries or link with --whole-archive). What I want is link (as in,…
Thibaut
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12
votes
1 answer
Binding failure with objcopy --redefine-syms
Preconditions
A third-party has provided a C++ executable fooapp that uses a shared object libfoo.so. The library also comes with a header foo.hpp so developers can build other applications:
/* foo.hpp */
namespace foo {
void bar(int a, int b);
…
BrianTheLion
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11
votes
5 answers
LD_PRELOAD with setuid binary
I am trying to use LD_PRELOAD to preload a library with an application that has setuid permissions. Tried LD_PRELOAD at first, and it seemed like it was being ignored with the setuid binary, though it was working when I tried it with others like ls,…
Mark Lobo
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8
votes
1 answer
LD_PRELOAD does not loaded on systemd
I am trying to inject a SO into a process that starts using systemd init system (using LD_PRELOAD), but it does not loaded into the new process.
I complied a basic SO (unrandom.c):
int rand(){
return 42; //the most random number in the…
Or Smolnik
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8
votes
2 answers
hiding functions in C
I have application that has a function f1 void f1 ()
In addition, I have a library that I load using LD_PRELOAD.
The library has several code files and several header file, and it compiled to .so file.
On of the header files also uses a function…
dk7
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7
votes
1 answer
why is library loaded via LD_PRELOAD operating before initialization?
In the following minimal example, a library loaded via LD_PRELOAD with functions to intercept fopen and openat is apparently operating before its initialization. (Linux is CentOS 7.3). Why??
library file comm.c:
#define _GNU_SOURCE
#include…
Mark Galeck
- 5,261
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7
votes
1 answer
How to check if a linux shared library has been preloaded using LD_PRELOAD
I'm familiar with using dlopen() to check if a shared library has been loaded into a process using a prior call to dlopen() without triggering a load if it isn't present, like so:
void* lib = dlopen(lib_name, RTLD_NOLOAD);
if (lib != NULL) {
…
Timo Geusch
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7
votes
1 answer
Dynamically modify symbol table at runtime (in C)
Is it possible to dynamically modify symbol table at runtime in C (in elf format on Linux)?
My eventual goal is the following:
Inside certain function say foo, I want to override malloc function to my custom handler my_malloc. But outside foo, any…
Richard
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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
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6
votes
5 answers
Problems with LD_PRELOAD and calloc() interposition for certain executables
Relating to a previous question of mine
I've successfully interposed malloc, but calloc seems to be more problematic.
That is with certain hosts, calloc gets stuck in an infinite loop with a possible internal calloc call inside dlsym. However, a…
Justicle
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6
votes
1 answer
LD_PRELOAD only working for malloc, not free
I'm trying to interpose malloc/free/calloc/realloc etc with some interposers via LD_PRELOAD. In my small test, only malloc seems to be interposed, even though free is detected (see output).
I'd expect the output to contain a line "NANO: free(x)" -…
Justicle
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6
votes
3 answers
LD_PRELOAD doesn't affect dlopen() with RTLD_NOW
If I use a function from a shared library directly, i.e. by declaring it in my code and linking during compile time, LD_PRELOAD works fine. But if I use dlopen()/dlsym() instead LD_PRELOAD has no effect!
The problem is that I want to debug a program…
sashoalm
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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
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