I've found how to make my C code right: in the parent and child, I have to close the ends of the pipe that I won't be using. My code becomes:

#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

static char buf[512];

int main()
{
    int pfd[2];
    pipe( pfd );

    pid_t pid = fork();
    if ( pid ) {
        /* parent */
        close( pfd[1] );
        ssize_t s = read( pfd[0], buf, sizeof(buf) );
        waitpid( pid, NULL, 0 );
    }
    else {
        /* child */
        close( pfd[0] );
        dup2( pfd[1], STDOUT_FILENO );
        close( STDOUT_FILENO );
    }

    return 0;
}
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This seems to be bulletproof. How can I get that using Perl?