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[PATCH] assume sprintf formatting of wide characters may fail (PR 86853)


The sprintf handling of wide characters neglects to consider
that calling the function may fail due to a conversion error
(when the wide character is invalid or not representable in
the current locale).  The handling also misinterprets
the POSIX %S wide string directive as a plain narrow %s and
doesn't include %C (the POSIX equivalent of %lc).  The attached
patch corrects these oversights by extending the data structures
to indicate when a directive may fail, and extending the UNDER4K
member of the format_result structure to also encode calls with
such directives.

Tested on x86_64-linux.

Besides the trunk, since this bug can affect code correctness
I'd like to backport this patch to both release branches (7
and 8).

Martin
PR tree-optimization/86853 - sprintf optimization for wide strings doesn't account for conversion failure

gcc/ChangeLog:

	PR tree-optimization/86853
	* gimple-ssa-sprintf.c (struct format_result): Rename member.
	(struct fmtresult): Add member and initialize it in ctors.
	(format_character): Handle %C.  Extend range to NUL.  Set MAYFAIL.
	(format_string): Handle %S the same as %ls.  Set MAYFAIL.
	(format_directive): Set POSUNDER4K when MAYFAIL is set.
	(parse_directive): Handle %C same as %c.
	(sprintf_dom_walker::compute_format_length): Adjust.
	(is_call_safe): Adjust.

gcc/testsuite/ChangeLog:

	PR tree-optimization/86853
	* gcc.dg/tree-ssa/builtin-sprintf-10.c: New test.
	* gcc.dg/tree-ssa/builtin-sprintf-11.c: New test.
	* gcc.dg/tree-ssa/builtin-sprintf-warn-18.c: Adjust.

Index: gcc/gimple-ssa-sprintf.c
===================================================================
--- gcc/gimple-ssa-sprintf.c	(revision 263295)
+++ gcc/gimple-ssa-sprintf.c	(working copy)
@@ -211,12 +211,14 @@ struct format_result
      the return value optimization.  */
   bool knownrange;
 
-  /* True if no individual directive resulted in more than 4095 bytes
-     of output (the total NUMBER_CHARS_{MIN,MAX} might be greater).
-     Implementations are not required to handle directives that produce
-     more than 4K bytes (leading to undefined behavior) and so when one
-     is found it disables the return value optimization.  */
-  bool under4k;
+  /* True if no individual directive could fail or result in more than
+     4095 bytes of output (the total NUMBER_CHARS_{MIN,MAX} might be
+     greater).  Implementations are not required to handle directives
+     that produce more than 4K bytes (leading to undefined behavior)
+     and so when one is found it disables the return value optimization.
+     Similarly, directives that can fail (such as wide character
+     directives) disable the optimization.  */
+  bool posunder4k;
 
   /* True when a floating point directive has been seen in the format
      string.  */
@@ -650,7 +652,7 @@ struct fmtresult
   fmtresult (unsigned HOST_WIDE_INT min = HOST_WIDE_INT_MAX)
   : argmin (), argmax (),
     knownrange (min < HOST_WIDE_INT_MAX),
-    nullp ()
+    mayfail (), nullp ()
   {
     range.min = min;
     range.max = min;
@@ -664,7 +666,7 @@ struct fmtresult
 	     unsigned HOST_WIDE_INT likely = HOST_WIDE_INT_MAX)
   : argmin (), argmax (),
     knownrange (min < HOST_WIDE_INT_MAX && max < HOST_WIDE_INT_MAX),
-    nullp ()
+    mayfail (), nullp ()
   {
     range.min = min;
     range.max = max;
@@ -694,6 +696,10 @@ struct fmtresult
      heuristics that depend on warning levels.  */
   bool knownrange;
 
+  /* True for a directive that may fail (such as wide character
+     directives).  */
+  bool mayfail;
+
   /* True when the argument is a null pointer.  */
   bool nullp;
 };
@@ -2202,7 +2208,8 @@ format_character (const directive &dir, tree arg,
 
   res.knownrange = true;
 
-  if (dir.modifier == FMT_LEN_l)
+  if (dir.specifier == 'C'
+      || dir.modifier == FMT_LEN_l)
     {
       /* A wide character can result in as few as zero bytes.  */
       res.range.min = 0;
@@ -2217,13 +2224,20 @@ format_character (const directive &dir, tree arg,
 	      res.range.likely = 0;
 	      res.range.unlikely = 0;
 	    }
-	  else if (min > 0 && min < 128)
+	  else if (min >= 0 && min < 128)
 	    {
+	      /* Be conservative if the target execution character set
+		 is not a 1-to-1 mapping to the source character set or
+		 if the source set is not ASCII.  */
+	      bool one_2_one_ascii
+		= (target_to_host_charmap[0] == 1 && target_to_host ('a') == 97);
+
 	      /* A wide character in the ASCII range most likely results
 		 in a single byte, and only unlikely in up to MB_LEN_MAX.  */
-	      res.range.max = 1;
+	      res.range.max = one_2_one_ascii ? 1 : target_mb_len_max ();;
 	      res.range.likely = 1;
 	      res.range.unlikely = target_mb_len_max ();
+	      res.mayfail = !one_2_one_ascii;
 	    }
 	  else
 	    {
@@ -2232,6 +2246,8 @@ format_character (const directive &dir, tree arg,
 	      res.range.max = target_mb_len_max ();
 	      res.range.likely = 2;
 	      res.range.unlikely = res.range.max;
+	      /* Converting such a character may fail.  */
+	      res.mayfail = true;
 	    }
 	}
       else
@@ -2241,6 +2257,7 @@ format_character (const directive &dir, tree arg,
 	  res.range.max = target_mb_len_max ();
 	  res.range.likely = 2;
 	  res.range.unlikely = res.range.max;
+	  res.mayfail = true;
 	}
     }
   else
@@ -2276,7 +2293,8 @@ format_string (const directive &dir, tree arg, vr_
       /* A '%s' directive with a string argument with constant length.  */
       res.range = slen.range;
 
-      if (dir.modifier == FMT_LEN_l)
+      if (dir.specifier == 'S'
+	  || dir.modifier == FMT_LEN_l)
 	{
 	  /* In the worst case the length of output of a wide string S
 	     is bounded by MB_LEN_MAX * wcslen (S).  */
@@ -2302,6 +2320,10 @@ format_string (const directive &dir, tree arg, vr_
 	  /* Even a non-empty wide character string need not convert into
 	     any bytes.  */
 	  res.range.min = 0;
+
+	  /* A non-emtpy wide character conversion may fail.  */
+	  if (slen.range.max > 0)
+	    res.mayfail = true;
 	}
       else
 	{
@@ -2340,7 +2362,8 @@ format_string (const directive &dir, tree arg, vr_
 	 at level 2.  This result is adjust upward for width (if it's
 	 specified).  */
 
-      if (dir.modifier == FMT_LEN_l)
+      if (dir.specifier == 'S'
+	  || dir.modifier == FMT_LEN_l)
 	{
 	  /* A wide character converts to as few as zero bytes.  */
 	  slen.range.min = 0;
@@ -2352,6 +2375,10 @@ format_string (const directive &dir, tree arg, vr_
 
 	  if (slen.range.likely < target_int_max ())
 	    slen.range.unlikely *= target_mb_len_max ();
+
+	  /* A non-emtpy wide character conversion may fail.  */
+	  if (slen.range.max > 0)
+	    res.mayfail = true;
 	}
 
       res.range = slen.range;
@@ -2904,11 +2931,14 @@ format_directive (const sprintf_dom_walker::call_i
      of 4095 bytes required to be supported?  */
   bool minunder4k = fmtres.range.min < 4096;
   bool maxunder4k = fmtres.range.max < 4096;
-  /* Clear UNDER4K in the overall result if the maximum has exceeded
-     the 4k (this is necessary to avoid the return valuye optimization
+  /* Clear POSUNDER4K in the overall result if the maximum has exceeded
+     the 4k (this is necessary to avoid the return value optimization
      that may not be safe in the maximum case).  */
   if (!maxunder4k)
-    res->under4k = false;
+    res->posunder4k = false;
+  /* Also clear POSUNDER4K if the directive may fail.  */
+  if (fmtres.mayfail)
+    res->posunder4k = false;
 
   if (!warned
       /* Only warn at level 2.  */
@@ -3354,12 +3384,15 @@ parse_directive (sprintf_dom_walker::call_info &in
       dir.fmtfunc = format_none;
       break;
 
+    case 'C':
     case 'c':
+      /* POSIX wide character and C/POSIX narrow character.  */
       dir.fmtfunc = format_character;
       break;
 
     case 'S':
     case 's':
+      /* POSIX wide string and C/POSIX narrow character string.  */
       dir.fmtfunc = format_string;
       break;
 
@@ -3517,10 +3550,10 @@ sprintf_dom_walker::compute_format_length (call_in
   res->range.min = res->range.max = 0;
 
   /* No directive has been seen yet so the length of output is bounded
-     by the known range [0, 0] (with no conversion producing more than
-     4K bytes) until determined otherwise.  */
+     by the known range [0, 0] (with no conversion resulting in a failure
+     or producing more than 4K bytes) until determined otherwise.  */
   res->knownrange = true;
-  res->under4k = true;
+  res->posunder4k = true;
   res->floating = false;
   res->warned = false;
 
@@ -3588,7 +3621,7 @@ is_call_safe (const sprintf_dom_walker::call_info
 	      const format_result &res, bool under4k,
 	      unsigned HOST_WIDE_INT retval[2])
 {
-  if (under4k && !res.under4k)
+  if (under4k && !res.posunder4k)
     return false;
 
   /* The minimum return value.  */
Index: gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-10.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-10.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-10.c	(working copy)
@@ -0,0 +1,119 @@
+/* PR tree-optimization/86853 - sprintf optimization for wide strings
+   doesn't account for conversion failureâ??
+   { dg-do compile }
+   { dg-options "-O2 -Wall -fdump-tree-optimized" } */
+
+typedef __SIZE_TYPE__  size_t;
+typedef __WCHAR_TYPE__ wchar_t;
+
+extern int snprintf (char*, size_t, const char*, ...);
+
+#define CONCAT(x, y) x ## y
+#define CAT(x, y) CONCAT (x, y)
+#define FAILNAME(name) CAT (call_ ## name ##_on_line_, __LINE__)
+
+#define FAIL(name) do {				\
+    extern void FAILNAME (name) (void);		\
+    FAILNAME (name)();				\
+  } while (0)
+
+/* Macro to emit a call to funcation named
+     call_in_true_branch_not_eliminated_on_line_NNN()
+   for each call that's expected to be eliminated.  The dg-final
+   scan-tree-dump-time directive at the bottom of the test verifies
+   that no such call appears in output.  */
+#define ELIM(expr) \
+  if (!(expr)) FAIL (in_true_branch_not_eliminated); else (void)0
+
+/* Macro to emit a call to a function named
+     call_made_in_{true,false}_branch_on_line_NNN()
+   for each call that's expected to be retained.  The dg-final
+   scan-tree-dump-time directive at the bottom of the test verifies
+   that the expected number of both kinds of calls appears in output
+   (a pair for each line with the invocation of the KEEP() macro.  */
+#define KEEP(expr)				\
+  if (expr)					\
+    FAIL (made_in_true_branch);			\
+  else						\
+    FAIL (made_in_false_branch)
+
+
+extern wchar_t wc;
+extern wchar_t ws[];
+
+const wchar_t ws3[] = L"12\xff";
+
+/* Verify that the following calls are eliminated.  */
+
+void elim_wide_char_call (void)
+{
+  ELIM (snprintf (0, 0, "%lc", L'\0'));
+  ELIM (snprintf (0, 0, "%lc", L'1'));
+  ELIM (snprintf (0, 0, "%lc", L'a'));
+  ELIM (snprintf (0, 0, "%lc", ws3[0]));
+  ELIM (snprintf (0, 0, "%lc", ws3[1]));
+  ELIM (snprintf (0, 0, "%lc", ws3[3]));
+
+  ELIM (snprintf (0, 0, "%C", L'\0'));
+  ELIM (snprintf (0, 0, "%C", L'9'));
+  ELIM (snprintf (0, 0, "%C", L'z'));
+  ELIM (snprintf (0, 0, "%C", ws3[0]));
+  ELIM (snprintf (0, 0, "%C", ws3[1]));
+  ELIM (snprintf (0, 0, "%C", ws3[3]));
+
+  /* Verify an unknown character value within the ASCII range.  */
+  if (wc < 1 || 127 < wc)
+    wc = 0;
+
+  ELIM (snprintf (0, 0, "%C", wc));
+  ELIM (snprintf (0, 0, "%C", wc));
+}
+
+void elim_wide_string_call (void)
+{
+  ELIM (snprintf (0, 0, "%ls", L""));
+}
+
+
+#line 1000
+
+  /* Verify that the following calls are not eliminated.  */
+
+void keep_wide_char_call (void)
+{
+  KEEP (snprintf (0, 0, "%lc", L'\xff'));
+  KEEP (snprintf (0, 0, "%lc", L'\xffff'));
+  KEEP (snprintf (0, 0, "%lc", wc));
+  KEEP (snprintf (0, 0, "%lc", ws3[2]));
+
+  KEEP (snprintf (0, 0, "%C", L'\xff'));
+  KEEP (snprintf (0, 0, "%C", L'\xffff'));
+  KEEP (snprintf (0, 0, "%C", wc));
+  KEEP (snprintf (0, 0, "%C", ws3[2]));
+
+  /* Verify an unknown character value outside the ASCII range
+     (with 128 being the only one).  */
+  if (wc < 32 || 128 < wc)
+    wc = 32;
+
+  KEEP (snprintf (0, 0, "%lc", wc));
+  KEEP (snprintf (0, 0, "%C", wc));
+}
+
+void keep_wide_string_call (void)
+{
+  KEEP (snprintf (0, 0, "%ls", L"\xff"));
+  KEEP (snprintf (0, 0, "%ls", L"\xffff"));
+  KEEP (snprintf (0, 0, "%ls", ws));
+  KEEP (snprintf (0, 0, "%ls", ws3));
+
+  KEEP (snprintf (0, 0, "%S", L"\xff"));
+  KEEP (snprintf (0, 0, "%S", L"\xffff"));
+  KEEP (snprintf (0, 0, "%S", ws));
+  KEEP (snprintf (0, 0, "%S", ws3));
+}
+
+/* { dg-final { scan-tree-dump-times "call_made_in_true_branch_not_eliminated" 0 "optimized" } }
+
+   { dg-final { scan-tree-dump-times "call_made_in_true_branch_on_line_1\[0-9\]\[0-9\]\[0-9\]" 18 "optimized" } }
+   { dg-final { scan-tree-dump-times "call_made_in_false_branch_on_line_1\[0-9\]\[0-9\]\[0-9\]" 18 "optimized" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-11.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-11.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-11.c	(working copy)
@@ -0,0 +1,65 @@
+/* PR tree-optimization/86853 - sprintf optimization for wide strings
+   doesn't account for conversion failureâ??
+   Exercise wide character handling in an EBCDIC execution charset.
+   { dg-do compile }
+   { dg-require-iconv "IBM1047" }
+   { dg-options "-O2 -Wall -Wno-format -Wformat-overflow -fexec-charset=IBM1047 -fdump-tree-optimized" } */
+
+typedef __WCHAR_TYPE__ wchar_t;
+
+/* Exercise wide character constants. */
+
+void test_lc_cst (void)
+{
+  /* IBM1047 0x30 maps to ASCII 0x94 which neeed not be representable
+     in the current locale (and the snprintf() call may fail).  Verify
+     that snprintf() doesn't assume it is.  */
+  wchar_t wc = 0x30;
+
+  int n = __builtin_snprintf (0, 0, "%lc", wc);
+  if (n < 0)
+    __builtin_abort ();
+}
+
+void test_C_cst (void)
+{
+  /* Same as above but for %C and 0x31 which maps to 0x95.  */
+  wchar_t wc = 0x31;
+
+  int n = __builtin_snprintf (0, 0, "%C", wc);
+  if (n < 0)
+    __builtin_abort ();
+}
+
+/* Exercise wide character values in known ranges. */
+
+void test_lc_range (wchar_t wc)
+{
+  if (wc < 0x40 || 0x49 < wc)
+    wc = 0x40;
+
+  int n = __builtin_snprintf (0, 0, "%lc", wc);
+  if (n < 0)
+    __builtin_abort ();
+}
+
+void test_C_range (wchar_t wc)
+{
+  if (wc < 0x41 || 0x48 < wc)
+    wc = 0x41;
+
+  int n = __builtin_snprintf (0, 0, "%C", wc);
+  if (n < 0)
+    __builtin_abort ();
+}
+
+/* Exercise unknown wide character values. */
+
+void test_var (wchar_t wc)
+{
+  int n = __builtin_snprintf (0, 0, "%lc", wc);
+  if (n < 0)
+    __builtin_abort ();
+}
+
+/* { dg-final { scan-tree-dump-times "abort" 5 "optimized" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-warn-18.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-warn-18.c	(revision 263295)
+++ gcc/testsuite/gcc.dg/tree-ssa/builtin-sprintf-warn-18.c	(working copy)
@@ -18,7 +18,7 @@ void test_characters ()
   T ("%A",    0.0);   /* { dg-warning ".%A. directive writing between 6 and 20 " } */
   T ("%a",    0.0);   /* { dg-warning ".%a. directive writing between 6 and 20 " } */
 
-  T ("%C",    'a');   /* { dg-warning ".%C. directive writing 1 byte" "bug 80537" { xfail *-*-* } } */
+  T ("%C",   L'a');   /* { dg-warning ".%C. directive writing up to 6 bytes" } */
   T ("%c",    'a');   /* { dg-warning ".%c. directive writing 1 byte" } */
 
   T ("%d",     12);   /* { dg-warning ".%d. directive writing 2 bytes" } */
@@ -93,7 +93,8 @@ void test_characters ()
   T ("%x",    1234);  /* { dg-warning ".%x. directive writing 3 bytes" } */
   T ("%#X",   1235);  /* { dg-warning ".%#X. directive writing 5 bytes" } */
 
-  T ("%S",    L"1");  /* { dg-warning ".%S. directive writing 1 byte" } */
+  T ("%S",    L"1");  /* { dg-warning ".%S. directive writing up to 6 bytes" } */
+  T ("%ls",  L"12");  /* { dg-warning ".%ls. directive writing up to 12 bytes" } */
   T ("%-s",    "1");  /* { dg-warning ".%-s. directive writing 1 byte" } */
 
   /* Verify that characters in the source character set appear in

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