gas: Fix internal error on long local labels

Prior to this commit, on an input such as "88888888888:", GAS hits a
signed integer overflow and likely an assertion failure. I see:

$ echo "88888888888:" | bin/aarch64-none-elf-as
{standard input}: Assembler messages:
{standard input}:1: Internal error in fb_label_name at ../gas/symbols.c:2049.
Please report this bug.

To fix this issue, I've taken two steps:

1. Change the type used for processing local labels in
   read_a_source_file() from int to long, to allow representing more
   local labels, and also since all uses of this variable (temp) are
   actually of type long.

2. Detect if we would overflow and bail out with an error message
   instead of actually overflowing and hitting the assertion in
   fb_label_name().

gas/ChangeLog:

2020-08-06  Alex Coplan  <alex.coplan@arm.com>

	* read.c (read_a_source_file): Use long for local labels, detect
	overflow and raise an error for overly-long labels.
	* testsuite/gas/all/gas.exp: Add local-label-overflow test.
	* testsuite/gas/all/local-label-overflow.d: New test.
	* testsuite/gas/all/local-label-overflow.l: Error output.
	* testsuite/gas/all/local-label-overflow.s: Input.

1 files changed, 16 insertions, 3 deletions

diff --git a/gas/read.c b/gas/read.c
index f192cc1..bd89658 100644
--- a/gas/read.c
+++ b/gas/read.c
@@ -40,6 +40,8 @@
 #include "dw2gencfi.h"
 #include "wchar.h"
 
+#include <limits.h>
+
 #ifndef TC_START_LABEL
 #define TC_START_LABEL(STR, NUL_CHAR, NEXT_CHAR) (NEXT_CHAR == ':')
 #endif
@@ -816,7 +818,7 @@ read_a_source_file (const char *name)
   char nul_char;
   char next_char;
   char *s;		/* String of symbol, '\0' appended.  */
-  int temp;
+  long temp;
   pseudo_typeS *pop;
 
 #ifdef WARN_COMMENTS
@@ -1212,10 +1214,21 @@ read_a_source_file (const char *name)
 	      /* Read the whole number.  */
 	      while (ISDIGIT (*input_line_pointer))
 		{
-		  temp = (temp * 10) + *input_line_pointer - '0';
+		  const long digit = *input_line_pointer - '0';
+		  if (temp > (LONG_MAX - digit) / 10)
+		    {
+		      as_bad (_("local label too large near %s"), backup);
+		      temp = -1;
+		      break;
+		    }
+		  temp = temp * 10 + digit;
 		  ++input_line_pointer;
 		}
 
+	      /* Overflow: stop processing the label.  */
+	      if (temp == -1)
+		continue;
+
 	      if (LOCAL_LABELS_DOLLAR
 		  && *input_line_pointer == '$'
 		  && *(input_line_pointer + 1) == ':')
@@ -1224,7 +1237,7 @@ read_a_source_file (const char *name)
 
 		  if (dollar_label_defined (temp))
 		    {
-		      as_fatal (_("label \"%d$\" redefined"), temp);
+		      as_fatal (_("label \"%ld$\" redefined"), temp);
 		    }
 
 		  define_dollar_label (temp);