`dl_iterate_phdr` assumes GNU/Linux

[workingjubilee]

Only GNU/Linux guarantees:

• the name of the executable is ""
• the executable is the first callback

This doesn't seem to be guaranteed to be true, even on other flavors of Linux, which may have a sense of humor, e.g. musl's choices in the static linkage case:

        info.dlpi_addr  = base;
	info.dlpi_name  = "/proc/self/exe";
	info.dlpi_phdr  = (void *)aux[AT_PHDR];
	info.dlpi_phnum = aux[AT_PHNUM];
	info.dlpi_adds  = 0;
	info.dlpi_subs  = 0;
	if (tls_phdr) {
		info.dlpi_tls_modid = 1;
		info.dlpi_tls_data = __tls_get_addr((tls_mod_off_t[]){1,0});
	} else {
		info.dlpi_tls_modid = 0;
		info.dlpi_tls_data = 0;
	}
	return (callback)(&info, sizeof (info), data);

[workingjubilee]

See also https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199943