Explicitly test for broken strnvis.

NetBSD added an strnvis and unfortunately made it incompatible with the
existing one in OpenBSD and Linux's libbsd (the former having existed
for over ten years). Despite this incompatibility being reported during
development (see http://gnats.netbsd.org/44977) they still shipped it.
Even more unfortunately FreeBSD and later MacOS picked up this incompatible
implementation.  Try to detect this mess, and assume the only safe option
if we're cross compiling.

OpenBSD 2.9 (2001): strnvis(char *dst, const char *src, size_t dlen, int flag);
NetBSD 6.0 (2012):  strnvis(char *dst, size_t dlen, const char *src, int flag);

ok djm@

1 files changed, 35 insertions, 4 deletions

diff --git a/configure.ac b/configure.ac
index 373d21b3..de63a0f5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -846,8 +846,6 @@ mips-sony-bsd|mips-sony-newsos4)
 	AC_DEFINE([SSH_TUN_PREPEND_AF], [1],
 	    [Prepend the address family to IP tunnel traffic])
 	TEST_MALLOC_OPTIONS="AJRX"
-	AC_DEFINE([BROKEN_STRNVIS], [1],
-	    [NetBSD strnvis argument order is swapped compared to OpenBSD])
 	AC_DEFINE([BROKEN_READ_COMPARISON], [1],
 	    [NetBSD read function is sometimes redirected, breaking atomicio comparisons against it])
 	;;
@@ -858,8 +856,6 @@ mips-sony-bsd|mips-sony-newsos4)
 	AC_CHECK_HEADER([net/if_tap.h], ,
 	    AC_DEFINE([SSH_TUN_NO_L2], [1], [No layer 2 tunnel support]))
 	AC_DEFINE([BROKEN_GLOB], [1], [FreeBSD glob does not do what we need])
-	AC_DEFINE([BROKEN_STRNVIS], [1],
-	    [FreeBSD strnvis argument order is swapped compared to OpenBSD])
 	TEST_MALLOC_OPTIONS="AJRX"
 	# Preauth crypto occasionally uses file descriptors for crypto offload
 	# and will crash if they cannot be opened.
@@ -2333,6 +2329,41 @@ if test "x$check_for_conflicting_getspnam" = "x1"; then
 	)
 fi
 
+dnl NetBSD added an strnvis and unfortunately made it incompatible with the
+dnl existing one in OpenBSD and Linux's libbsd (the former having existed
+dnl for over ten years). Despite this incompatibility being reported during
+dnl development (see http://gnats.netbsd.org/44977) they still shipped it.
+dnl Even more unfortunately FreeBSD and later MacOS picked up this incompatible
+dnl implementation.  Try to detect this mess, and assume the only safe option
+dnl if we're cross compiling.
+dnl
+dnl OpenBSD, 2001: strnvis(char *dst, const char *src, size_t dlen, int flag);
+dnl NetBSD: 2012,  strnvis(char *dst, size_t dlen, const char *src, int flag);
+if test "x$ac_cv_func_strnvis" = "xyes"; then
+	AC_MSG_CHECKING([for working strnvis])
+	AC_RUN_IFELSE(
+		[AC_LANG_PROGRAM([[
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <vis.h>
+static void sighandler(int sig) { _exit(1); }
+		]], [[
+	char dst[16];
+
+	signal(SIGSEGV, sighandler);
+	if (strnvis(dst, "src", 4, 0) && strcmp(dst, "src") == 0)
+		exit(0);
+	exit(1)
+		]])],
+		[AC_MSG_RESULT([yes])],
+		[AC_MSG_RESULT([no])
+		 AC_DEFINE([BROKEN_STRNVIS], [1], [strnvis detected broken])],
+		[AC_MSG_WARN([cross compiling: assuming broken])
+		 AC_DEFINE([BROKEN_STRNVIS], [1], [strnvis assumed broken])]
+	)
+fi
+
 AC_FUNC_GETPGRP
 
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