[Issue 1679] New: D should cast char[] to char* when used in a variadic argument in extern(C) context

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=1679

           Summary: D should cast char[] to char* when used in a variadic
                    argument in extern(C) context
           Product: D
           Version: unspecified
          Platform: PC
               URL: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=451707
        OS/Version: Linux
            Status: NEW
          Severity: critical
          Priority: P5
         Component: DMD
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: arthur.loiret at gmail.com


The following code:

--------------------------------------------------
import std.c.process;
int main(char args[][]) {
    execl("/bin/sh", "sh", "-c", "ls", null);
    printf("%m\n");
    return -1;
}
--------------------------------------------------

Doesn't work:

Bad address
zsh: exit 255   ./test

exelc prototype is:
extern(C) int exelc(char *, char *, ...) because if I do that:

And the following code works:
--------------------------------------------------
extern(C) int execl(char *path, char *arg, char*, char*, char*, ...);
int main(char args[][]) {
    execl("/bin/sh", "sh", "-c", "ls", null);
    printf("%m\n");
    return -1;
}
--------------------------------------------------

So does this one:
--------------------------------------------------
import std.c.process;
int main(char args[][]) {
    execl("/bin/sh", "sh", cast(char*)"-c", cast(char*)"ls", null);
    printf("%m\n");
    return -1;
}
--------------------------------------------------


Pierre Habouzit understood the issue, here is his explanation:

  When the "-c" argument is sent as the first
argument of the variadic part, D sends a char[] and not a char*, meaning
that it puts 2, "-c" on the stack, which confuses the C.
  I believe that D should do the implicit cast in that case, as it'll
break a _lot_ of programs using C APIs and variadic arguments in very
subtle ways.


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