[patch] fix phony_iconv wide character support

[Sandra Loosemore <sandra at codesourcery dot com>]

A while back I submitted a patch to skip gdb.base/wchar.exp tests when 
GDB is built with PHONY_ICONV enabled:

https://sourceware.org/ml/gdb-patches/2015-09/msg00388.html

The consensus from the discussion seemed to be that it would be better 
to fix the PHONY_ICONV support instead, so that's what this patch does.

I found a whole bunch of bugs in the existing code....

(1) phony_iconv_open had code to recognize "UTF-32BE" as a wide 
character set, but GDB_DEFAULT_TARGET_WIDE_CHARSET was set to 
"ISO-8859-1" instead, so the decoding wasn't getting triggered.

(2) phony_iconv wasn't advancing *inbuf properly after processing each 
4-byte group, plus it wasn't checking for output overflow.  I don't see 
how the old code could ever have worked even if you explicitly chose 
UTF-32BE.

(3) I was doing experiments on a little-endian target (nios2-linux-gnu), 
so I had to extend the conversion code to handle both endiannesses.

(4) On Windows host, the system default (narrow) charset is CP1252 
rather than ISO-8859-1; this affects the behavior of functions like 
isprint, and in particular what is printed for the character constant 
cent ('\242') used in the testcase.  The testcase already checks for 
CP1252 but GDB wasn't reporting the default correctly.

So, my patch fixes all these things and the gdb.base/wchar.exp tests now 
all PASS in this configuration.  OK to commit?

-Sandra

2015-12-31  Sandra Loosemore  <sandra@codesourcery.com>

	gdb/
	* charset.c [PHONY_ICONV] (GDB_DEFAULT_HOST_CHARSET):
	Conditionalize for Windows host.
	(GDB_DEFAULT_TARGET_CHARSET): Match GDB_DEFAULT_HOST_CHARSET.
	(GDB_DEFAULT_TARGET_WIDE_CHARSET): Use UTF-32.
	(phony_iconv_open): Handle both UTF-32 endiannesses.
	(phony_iconv): Likewise.  Check for output overflow and clean up
	out-of-input cases.  Correct adjustment to input buffer pointer.
	(set_be_le_names) [PHONY_ICONV]: Use hard-wired names to match
	phony_iconv_open.

diff --git a/gdb/charset.c b/gdb/charset.c
index ee1ae20..82e5644 100644
--- a/gdb/charset.c
+++ b/gdb/charset.c
@@ -77,9 +77,13 @@
    arrange for there to be a single available character set.  */
 
 #undef GDB_DEFAULT_HOST_CHARSET
+#ifdef USE_WIN32API
+#define GDB_DEFAULT_HOST_CHARSET "CP1252"
+#else
 #define GDB_DEFAULT_HOST_CHARSET "ISO-8859-1"
-#define GDB_DEFAULT_TARGET_CHARSET "ISO-8859-1"
-#define GDB_DEFAULT_TARGET_WIDE_CHARSET "ISO-8859-1"
+#endif
+#define GDB_DEFAULT_TARGET_CHARSET GDB_DEFAULT_HOST_CHARSET 
+#define GDB_DEFAULT_TARGET_WIDE_CHARSET "UTF-32"
 #undef DEFAULT_CHARSET_NAMES
 #define DEFAULT_CHARSET_NAMES GDB_DEFAULT_HOST_CHARSET ,
 
@@ -95,20 +99,27 @@
 #undef ICONV_CONST
 #define ICONV_CONST const
 
+/* We allow conversions from UTF-32, wchar_t, and the host charset.
+   We allow conversions to wchar_t and the host charset
+   Return 1 if we are converting from UTF-32BE, 2 if from UTF32-LE,
+   0 otherwise.  This is  used as a flag in calls to iconv.  */
+
 static iconv_t
 phony_iconv_open (const char *to, const char *from)
 {
-  /* We allow conversions from UTF-32BE, wchar_t, and the host charset.
-     We allow conversions to wchar_t and the host charset.  */
-  if (strcmp (from, "UTF-32BE") && strcmp (from, "wchar_t")
-      && strcmp (from, GDB_DEFAULT_HOST_CHARSET))
-    return -1;
   if (strcmp (to, "wchar_t") && strcmp (to, GDB_DEFAULT_HOST_CHARSET))
     return -1;
 
-  /* Return 1 if we are converting from UTF-32BE, 0 otherwise.  This is
-     used as a flag in calls to iconv.  */
-  return !strcmp (from, "UTF-32BE");
+  if (!strcmp (from, "UTF-32BE") || !strcmp (from, "UTF-32"))
+    return 1;
+
+  if (!strcmp (from, "UTF-32LE"))
+    return 2;
+
+  if (strcmp (from, "wchar_t") && strcmp (from, GDB_DEFAULT_HOST_CHARSET))
+    return -1;
+
+  return 0;
 }
 
 static int
@@ -130,8 +141,17 @@ phony_iconv (iconv_t utf_flag, const char **inbuf, size_t *inbytesleft,
 
 	  for (j = 0; j < 4; ++j)
 	    {
-	      c <<= 8;
-	      c += (*inbuf)[j] & 0xff;
+	      if (utf_flag == 1)
+		{
+		  /* Big-endian.  */
+		  c <<= 8;
+		  c += (*inbuf)[j] & 0xff;
+		}
+	      else
+		{
+		  /* Little-endian.  */
+		  c += ((*inbuf)[j] & 0xff) << (8 * j);
+		}
 	    }
 
 	  if (c >= 256)
@@ -139,15 +159,21 @@ phony_iconv (iconv_t utf_flag, const char **inbuf, size_t *inbytesleft,
 	      errno = EILSEQ;
 	      return -1;
 	    }
+	  if (*outbytesleft < 1)
+	    {
+	      errno = E2BIG;
+	      return -1;
+	    }
 	  **outbuf = c & 0xff;
 	  ++*outbuf;
 	  --*outbytesleft;
 
-	  ++*inbuf;
+	  *inbuf += 4;
 	  *inbytesleft -= 4;
 	}
-      if (*inbytesleft < 4)
+      if (*inbytesleft)
 	{
+	  /* Partial sequence on input.  */
 	  errno = EINVAL;
 	  return -1;
 	}
@@ -165,12 +191,11 @@ phony_iconv (iconv_t utf_flag, const char **inbuf, size_t *inbytesleft,
       *outbuf += amt;
       *inbytesleft -= amt;
       *outbytesleft -= amt;
-    }
-
-  if (*inbytesleft)
-    {
-      errno = E2BIG;
-      return -1;
+      if (*inbytesleft)
+	{
+	  errno = E2BIG;
+	  return -1;
+	}
     }
 
   /* The number of non-reversible conversions -- but they were all
@@ -290,6 +315,10 @@ set_be_le_names (struct gdbarch *gdbarch)
     return;
   be_le_arch = gdbarch;
 
+#ifdef PHONY_ICONV
+  target_wide_charset_le_name = "UTF-32LE";
+  target_wide_charset_be_name = "UTF-32BE";
+#else
   target_wide_charset_le_name = NULL;
   target_wide_charset_be_name = NULL;
 
@@ -313,6 +342,7 @@ set_be_le_names (struct gdbarch *gdbarch)
 	    target_wide_charset_le_name = charset_enum[i];
 	}
     }
+# endif  /* PHONY_ICONV */
 }
 
 /* 'Set charset', 'set host-charset', 'set target-charset', 'set