gas: fix overflow diagnostics

While the logic in fixup_segment() so far was off by 1 for fixups
dealing with quantities without known signedness, thus failing to report
an overflow when e.g. a byte-sized resulting value is -0x100, the logic
in emit_expr_with_reloc() reported an overflow even on large negative
values when the respective positive ones would not be warned
about, and when fixup_segment() wouldn't do so either. Such diagnostics
all ought to follow a similar pattern of what value range is acceptable.
(If expressions' X_unsigned was reliably set, emit_expr_with_reloc()'s
checking might make sense to tighten based on that flag.)

Note that with commit 80aab57939a0 ("Changes to let cons handle bignums
like general expressions") having added handling of nbytes >
sizeof(valueT) in the O_constant case, converting to O_big, the setting
to zero of "hibit" had become dead. With "hibit" no longer used, this
code now gets dropped altogether. But additionally a respective know()
gets inserted.

1 files changed, 2 insertions, 9 deletions

diff --git a/gas/read.c b/gas/read.c
index 2f93e1b..db1011b 100644
--- a/gas/read.c
+++ b/gas/read.c
@@ -4505,24 +4505,19 @@ emit_expr_with_reloc (expressionS *exp,
       valueT get;
       valueT use;
       valueT mask;
-      valueT hibit;
       valueT unmask;
 
       /* JF << of >= number of bits in the object is undefined.  In
 	 particular SPARC (Sun 4) has problems.  */
       if (nbytes >= sizeof (valueT))
 	{
+	  know (nbytes == sizeof (valueT));
 	  mask = 0;
-	  if (nbytes > sizeof (valueT))
-	    hibit = 0;
-	  else
-	    hibit = (valueT) 1 << (nbytes * BITS_PER_CHAR - 1);
 	}
       else
 	{
 	  /* Don't store these bits.  */
 	  mask = ~(valueT) 0 << (BITS_PER_CHAR * nbytes);
-	  hibit = (valueT) 1 << (nbytes * BITS_PER_CHAR - 1);
 	}
 
       unmask = ~mask;		/* Do store these bits.  */
@@ -4534,9 +4529,7 @@ emit_expr_with_reloc (expressionS *exp,
 
       get = exp->X_add_number;
       use = get & unmask;
-      if ((get & mask) != 0
-	  && ((get & mask) != mask
-	      || (get & hibit) == 0))
+      if ((get & mask) != 0 && (-get & mask) != 0)
 	{
 	  /* Leading bits contain both 0s & 1s.  */
 	  as_warn (_("value 0x%" BFD_VMA_FMT "x truncated to 0x%" BFD_VMA_FMT "x"),