Throwing a C++ exception after an inline-asm jump
- by SoapBox
I have some odd self modifying code, but at the root of it is a pretty simple problem: I want to be able to execute a jmp (or a call) and then from that arbitrary point throw an exception and have it caught by the try/catch block that contained the jmp/call.
But when I do this (in gcc 4.4.1 x86_64) the exception results in a terminate() as it would if the exception was thrown from outside of a try/catch. I don't really see how this is different than throwing an exception from inside of some far-flung library, yet it obviously is because it just doesn't work.
How can I execute a jmp or call but still throw an exception back to the original try/catch? Why doesn't this try/catch continue to handle these exceptions as it would if the function was called normally?
The code:
#include <iostream>
#include <stdexcept>
using namespace std;
void thrower()
{
cout << "Inside thrower" << endl;
throw runtime_error("some exception");
}
int main()
{
cout << "Top of main" << endl;
try {
asm volatile (
"jmp *%0" // same thing happens with a call instead of a jmp
:
: "r"((long)thrower)
:
);
} catch (exception &e) {
cout << "Caught : " << e.what() << endl;
}
cout << "Bottom of main" << endl << endl;
}
The expected output:
Top of main
Inside thrower
Caught : some exception
Bottom of main
The actual output:
Top of main
Inside thrower
terminate called after throwing an instance of 'std::runtime_error'
what(): some exception
Aborted
