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so, in light of last night's discussion, i decided to throw together
a small proof of concept to illustrate my point. attached are three
files:
- check_hello.c, a simple "plugin" that prints hello world.
- a Makefile that illustrates just how easy it is to build a
shared object in the way i suggested
- dltest.c, a program that benchmarks one vs. the other by
executing the system/function calls 1000 times and recording
elapsed time in microseconds (i'd recommend piping stdout
to /dev/null)
this is what i get:
copelandia[~/nagiosplug/plugtest]09:41:03$ ./dltest >/dev/null
dlopen: 131
system: 3698327
sean
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#include
int main(){
printf("hello, world!\n");
}
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dltest: dltest.c
gcc -g -o dltest dltest.c -ldl
check_hello.o: check_hello.c
gcc -c check_hello.c
check_hello.shared.o: check_hello.c
gcc -c -fPIC -Dmain=check_hello check_hello.c
check_hello: check_hello.o
gcc -o check_hello check_hello.o
check_hello.so: check_hello.shared.o
ld -shared -o check_hello.so check_hello.o
test:
./dltest
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#include
#include
#include
#include
const char *ourgv[24] =3D{ "check_hello", NULL };
const char *ourcmd =3D "check_hello";
extern int optind;
int main(){
int i;
struct timeval start, midway, end;
long total_func, total_sys;
void *libhandle=3DNULL;=20
int (*check_func)(int, const char**)=3DNULL;
libhandle=3Ddlopen("./check_hello.so", RTLD_NOW);
if(libhandle=3D=3DNULL){
fprintf(stderr, "libhandle was null. damn. %s\n", dlerror());
}
*(void**)(&check_func) =3Ddlsym(libhandle, "check_hello");
if(check_func=3D=3DNULL || *check_func =3D=3D NULL){
fprintf(stderr, "check_func was null. damn. %s\n", dlerror());
}
=09
gettimeofday(&start, NULL);
for(i=3D0; i<1000; i++){
system(ourcmd);
}
gettimeofday(&midway, NULL);
for(i=3D0; i<1000; i++){
(*check_func)(1, ourgv);
}
gettimeofday(&end, NULL);
total_sys =3D ((midway.tv_sec - start.tv_sec)*1000000) + (midway.tv_usec -=
start.tv_usec);
total_func =3D ((end.tv_sec - midway.tv_sec)*1000000) + (end.tv_usec - mid=
way.tv_usec);
fprintf(stderr, "dlopen: %ld\n", total_func);
fprintf(stderr, "system: %ld\n", total_sys);
}
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