ubsan: signed integer overflow in atof_generic

[Alan Modra <amodra@gmail.com>]

Fix the signed overflows by using unsigned variables and detect
overflow at BUG! comment.

	* atof-generic.c (atof_generic): Avoid signed integer overflow.
	Return ERROR_EXPONENT_OVERFLOW if exponent overflows a long.

diff --git a/gas/atof-generic.c b/gas/atof-generic.c
index c3f818d9489..91583194868 100644
--- a/gas/atof-generic.c
+++ b/gas/atof-generic.c
@@ -72,11 +72,11 @@ atof_generic (/* return pointer to just AFTER number we read.  */
 	      const char *string_of_decimal_exponent_marks,
 	      FLONUM_TYPE *address_of_generic_floating_point_number)
 {
-  int return_value;		/* 0 means OK.  */
+  int return_value = 0;		/* 0 means OK.  */
   char *first_digit;
   unsigned int number_of_digits_before_decimal;
   unsigned int number_of_digits_after_decimal;
-  long decimal_exponent;
+  unsigned long decimal_exponent;
   unsigned int number_of_digits_available;
   char digits_sign_char;
 
@@ -204,7 +204,7 @@ atof_generic (/* return pointer to just AFTER number we read.  */
      deleting zeros after decimal.  In this case the decimal mark and
      the first zero digits after decimal mark are skipped.  */
   seen_significant_digit = 0;
-  signed long subtract_decimal_exponent = 0;
+  unsigned long subtract_decimal_exponent = 0;
 
   if (c && IS_DECIMAL_MARK (c))
     {
@@ -300,10 +300,11 @@ atof_generic (/* return pointer to just AFTER number we read.  */
 	{
 	  if (ISDIGIT (c))
 	    {
+	      if (decimal_exponent > LONG_MAX / 10
+		  || (decimal_exponent == LONG_MAX / 10
+		      && c > '0' + (char) (LONG_MAX - LONG_MAX / 10 * 10)))
+		return_value = ERROR_EXPONENT_OVERFLOW;
 	      decimal_exponent = decimal_exponent * 10 + c - '0';
-	      /*
-	       * BUG! If we overflow here, we lose!
-	       */
 	    }
 	  else
 	    {
@@ -327,7 +328,6 @@ atof_generic (/* return pointer to just AFTER number we read.  */
 
   number_of_digits_available =
     number_of_digits_before_decimal + number_of_digits_after_decimal;
-  return_value = 0;
   if (number_of_digits_available == 0)
     {
       address_of_generic_floating_point_number->exponent = 0;	/* Not strictly necessary */
@@ -505,7 +505,7 @@ atof_generic (/* return pointer to just AFTER number we read.  */
 	size_of_power_in_littlenums = precision;
 	/* Precision has a built-in fudge factor so we get a few guard bits.  */
 
-	decimal_exponent_is_negative = decimal_exponent < 0;
+	decimal_exponent_is_negative = (long) decimal_exponent < 0;
 	if (decimal_exponent_is_negative)
 	  {
 	    decimal_exponent = -decimal_exponent;

-- 
Alan Modra
Australia Development Lab, IBM