• Basile B. (33/35) Oct 24 2021 The following code, on linux
• Basile B. (8/11) Oct 24 2021 Forgot to say that this change
• jfondren (22/23) Oct 24 2021 I'm very surprised that this is even allowed. Apparently it's
• Basile B. (3/6) Oct 24 2021 ah yeah, and thanks, of course ... how would the count of arg be
• Brian Callahan (8/10) Oct 24 2021 The execve(2) is more explicit:

Basile B. <b2.temp gmx.com> writes:

The following code, on linux

```d
module runnable;
​
extern(C) int execv(const char* p, const char** args);
​
immutable src = `
     import std.getopt;
     void main(string[] args)
     {
         bool c;
         getopt(args, "c", &c);
     }
`;
​
void prepareProgram()
{
     import std.process  : execute;
     import std.file     : write;
     write("a.d", src);
     execute(["dmd", "a.d"]);
}
​
void main(string[] args)
{
     prepareProgram();
     execv("a", null);
}
```

results in a std.getopt exception:

 object.Exception /usr/include/dmd/phobos/std/getopt.d(423): 
 Invalid arguments string passed: program name missing

Context is a program not written in D that uses execv to call a D 
program that uses getopt.

What do you think ?

Basile B. <b2.temp gmx.com> writes:

On Sunday, 24 October 2021 at 14:21:52 UTC, Basile B. wrote:
 The following code, on linux
 [...]
 What do you think ?

Forgot to say that this change

```diff
- execv("a", null);
+ execv("a", ["whatever".ptr].ptr);
```

makes the problem goes away, so it would be caused by how `null` 
args are handled, presumably.

jfondren <julian.fondren gmail.com> writes:

On Sunday, 24 October 2021 at 14:21:52 UTC, Basile B. wrote:
 What do you think ?

I'm very surprised that this is even allowed. Apparently it's 
Linux userspace that normally complains about it: 
https://git.savannah.gnu.org/cgit/gnulib.git/tree/lib/progname.c#n54

The manpages just say

```
    v - execv(), execvp(), execvpe()
        The char *const argv[] argument is an array of pointers to 
null-terminated strings  that  represent
        the argument list available to the new program.  The first 
argument, by convention, should point to
        the filename associated with the file being executed.  The 
array of pointers must be terminated  by
        a null pointer.
```

With nothing to the contrary, I'd take "must be terminated by a 
null pointer" as "can't itself be a null pointer".

On OpenBSD this fails outright:

```
RET   execve -1 errno 14 Bad address
```

You can get `execv` from `core.sys.posix.unistd`

Basile B. <b2.temp gmx.com> writes:

On Sunday, 24 October 2021 at 14:38:44 UTC, jfondren wrote:
 [...]

 With nothing to the contrary, I'd take "must be terminated by a 
 null pointer" as "can't itself be a null pointer".

ah yeah, and thanks, of course ... how would the count of arg be 
known without the sentinel...

Brian Callahan <bcallah openbsd.org> writes:

On Sunday, 24 October 2021 at 14:38:44 UTC, jfondren wrote:
 With nothing to the contrary, I'd take "must be terminated by a 
 null pointer" as "can't itself be a null pointer".

The execve(2) is more explicit:
"The argument argv is a pointer to a null-terminated array of 
character pointers to NUL-terminated character strings. These 
strings construct the argument list to be made available to the 
new process. At least one non-null argument must be present in 
the array; by custom, the first element should be the name of the 
executed program (for example, the last component of path)."