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I have this function:

int execve(const char* filename, char* const argv[], char* const envp[]);

And I need set to NULL the envp parameter, so I need a pointer to NULL in the edx register before execute the function (better said, the syscall with int 0x80). The question is, can I do:

mov eax, 0
mov edx, eax  ; edx points to NULL, no to some address that contains NULL

or need I do:

push 0
mov edx, esp ; edx points to some address that contains NULL
Rob
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1 Answers1

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It depends on the operation system. In Linux you can use directly a NULL pointer.

man execve:

On Linux, argv and envp can be specified as NULL. In both cases, this has the same effect as specifying the argument as a pointer to a list containing a single null pointer. Do not take advantage of this misfeature! It is nonstandard and nonportable: on most other UNIX systems doing this will result in an error (EFAULT).

rkhb
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