exceptions: hack to store errno in string object.

Basic idea: when we throw an exception that pertains to a
system error which has an errno code, we can stick the errno
into the memory area of the character string, into the wchar_t
that immediately follows the null terminator. We can do this
because strings track their actual allocation size.

A pair of setter/getter functions to set and retrieve this
value are provided, and all functions in the code which can
set such a code are updated to do so, simply by calling the
newly added uw_ethrowf that drop-in replaces for uw_throwf.

* lib.[ch] (string_set_code, string_get_code): New functions.

* unwind.[ch] (uw_ethrowf): New function.

* eval.c (eval_init): Register string-set-code and
string-get-code intrinsics.

* ftw.c (ftw_wrap): Switch to uw_ethrowf.

* parser.c (open_txr_file): Likewise.

* socket.c (dgram_overflow): Store the ENOBUFS error in errno,
and use uw_ethrowf instead uw_throwf.
(dgram_get_byte_callback, dgram_flush, sock_bind, to_connect,
open_sockfd, sock_connect, sock_listen, sock_accept,
sock_shutdown, sock_timeout, socketpair_wrap): Switch to
uw_ethrowf.

* stream.c (dev_null_get_fd, stdio_maybe_read_error,
stdio_maybe_error, stdio_close, pipe_close, open_directory,
open_file, open_fileno, open_tail, fds_subst,
open_subprocess, open_command, remove_path, rename_path,
tmpfile_wrap, mkdtemp_wrap, mkstemp_wrap): Switch to uw_ethrowf.

* sysif.c (mkdir_wrap, ensure_dir, chdir_wrap, getcwd_wrap,
rmdir_wrap, mknod_wrap, mkfifo_wrap, chmod_wrap, do_chown,
symlink_wrap, link_wrap, readlink_wrap, close_wrap, val
exec_wrap, stat_impl, do_utimes, pipe_wrap, poll_wrap,
getgroups_wrap, setuid_wrap, seteuid_wrap, setgid_wrap,
setegid_wrap, setgroups_wrap, getresuid_wrap, setresuid_wrap,
setresgid_wrap, crypt_wrap, uname_wrap, opendir_wrap,
getrlimit_wrap, setrlimit_wrap): Likewise.

* termios.c (tcgetattr_wrap, tcsetattr_wrap, tcsendbreak_wrap,
tcdrain_wrap, tcflush_wrap, tcflow_wrap): Likewise.

* tests/018/errno.tl: New file.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.

1 files changed, 15 insertions, 0 deletions

diff --git a/unwind.c b/unwind.c
index 9d4c7586..efc321ef 100644
--- a/unwind.c
+++ b/unwind.c
@@ -33,6 +33,7 @@
 #include <assert.h>
 #include <stdarg.h>
 #include <signal.h>
+#include <errno.h>
 #include "config.h"
 #if HAVE_VALGRIND
 #include <valgrind/memcheck.h>
@@ -803,6 +804,20 @@ val uw_throwf(val sym, val fmt, ...)
   abort();
 }
 
+val uw_ethrowf(val sym, val fmt, ...)
+{
+  va_list vl;
+  val eno = num(errno);
+  val stream = make_string_output_stream();
+
+  va_start (vl, fmt);
+  (void) vformat(stream, fmt, vl);
+  va_end (vl);
+
+  uw_throw(sym, string_set_code(get_string_from_stream(stream), eno));
+  abort();
+}
+
 val uw_errorfv(val fmt, struct args *args)
 {
   val stream = make_string_output_stream();