Is it possible to intercept System Calls via Theos Tweak? Jailed Version - ios

Question

Can i intercept generic system calls like sqlite3_prepare or sqlite3_open also CC_MD5 of libcommonCrypto with a Theos (jailed versione) Tweak?
I would intercept all these calls and print on the console or into a log file.
I've read something about MSHookFunction, but i'm not sure about it.
EDIT: i add some code which i've wrote in these days. This is my Tweak.xm, where i would intercept CC_MD5 call, and after a simple message log, i would return to the normal flow. The tweak is injected, but i can not see any message.
#include <substrate.h>
#include <CommonCrypto/CommonDigest.h>
static unsigned char * (*original_CC_MD5)(const void *data, CC_LONG len, unsigned char *md);
static unsigned char * replaced_CC_MD5(const void *data, CC_LONG len, unsigned char *md) {
NSLog(#"Calling MD5");
return original_CC_MD5(data, len, md);
}
MSInitialize {
MSHookFunction(CC_MD5, replaced_CC_MD5, &original_CC_MD5);
}

Answer 1

I've found the problem. The Theos version that i'm using is for jailed device. With this version MSHookFunction is substituted by fishhook.
Using fishhook it's all ok: obviously the code changes
#include <substrate.h>
#include <CommonCrypto/CommonDigest.h>
#import <fishhook.h>
static unsigned char * (*original_CC_MD5)(const void *data, CC_LONG len, unsigned char *md);
static unsigned char * replaced_CC_MD5(const void *data, CC_LONG len, unsigned char *md) {
NSLog(#"Calling MD5");
return original_CC_MD5(data, len, md);
}
%ctor {
rebind_symbols((struct rebinding[1]){{"CC_MD5", replaced_CC_MD5, (void *)&original_CC_MD5}},1);
}