escaping double quotes inside an inline asm statement

[bobl]

I stuck with my inline example above cos the compiler listing is in normal gas assembly and not in the syntax specific to INLINE assembly which is illustrated in the program below.

To test that eax is loaded with the string's address I added "recipient" which I filled with eax's contents and printed out.
It gives the correct result i.e. /dev/vcsa1

"char device [] = "/dev/vcsa1"; corrupts the string.
const char * device = "/dev/vcsa1"; doesn't.

Code: Select all

#include <iostream>
using namespace std;
int main(){
const char * device = "/dev/vcsa1";
const char * recipient = "";
__asm__ __volatile__("movl  %%eax,%%ebx"
                     :"=b"(recipient)
                     :"a"(device), "b"(recipient)
                     );
cout << recipient << "\n";
return 0;
}

Your advice has been very much appreciated. Thank you.

[fronty]

I stuck with my inline example above cos the compiler listing is in normal gas assembly and not in the syntax specific to INLINE assembly which is illustrated in the program below.

What do you mean with compiler listing? Program listing (or source code, who prints source nowadays)? And if you want normal assembly, why don't you write plain assembly?

To test that eax is loaded with the string's address I added "recipient" which I filled with eax's contents and printed out.
It gives the correct result i.e. /dev/vcsa1

"char device [] = "/dev/vcsa1"; corrupts the string.
const char * device = "/dev/vcsa1"; doesn't.

What do you mean with "corrupting"? I don't see any reason that would corrupt anything.

I still don't see any reason in inline assembly, why can't you do something like this?

Code: Select all

#include <stdio.h>

int
main(void)
{
        char device[] = "/dev/vcsa1";
        char *recipient = device;

        printf("%s\n", recipient);

        return 0;
}

[bobl]

fronty just for you

Code: Select all

#include <iostream>
using namespace std;
int main(){
//const char * device = "/dev/vcsa1";
//const char * recipient = "";
char device [] = "/dev/vcsa1";
char recipient [] = "";
__asm__ __volatile__("movl  %%eax,%%ebx"
                     :"=b"(recipient)
                     :"a"(device), "b"(recipient)
                     );
cout << recipient << "\n";
return 0;
}

produces

Code: Select all

me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
@/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
Segmentation fault <device as [] recipient as const char * 
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
�/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
�/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
 /dev/vcsa1  <<< this isn't correct ie theres a space in front
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
P/dev/vcsa1
me@me-desktop:~$ 

Re corruption Take your pick.
By contrast if we switch back to const char *
we always get the correct result. There is a difference.
i.e.

Code: Select all

me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
/dev/vcsa1
me@me-desktop:~$ g++ fronty.cpp; ./a.out; rm a.out
/dev/vcsa1
me@me-desktop:~$

[qw]

Check the assembly output that GCC produces.