[PATCH] uniform behaviour of sleb128

[Tristan Gingold <gingold at adacore dot com>]

Hello,

the current sequence of bytes for this sleb128 depends on whether BFD_ARCH_SIZE is 32 or 64:

   1              		.data
   2 0000 FFFFFFFF 		.sleb128 281474976710655
   2      FFFF3F

or

   1              		.data
   2 0000 7F       		.sleb128 281474976710655

This is of course a real issue as gcc may generate this sleb128 number and gcc may hard
code the .debug_info section length.  In that case the object file is incorrect and
prevents debugging.

The patch fixes this issue by extended unsigned big number that would otherwise be reduced by sleb128.
(this is a complete rework of a previous patch).

No failure on i386-gnu-linux.

Ok to apply ?

Tristan.

diff --git a/gas/ChangeLog b/gas/ChangeLog
index 2d72b78..5f34823 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,11 @@
+2017-01-09  Tristan Gingold  <gingold@adacore.com>
+
+	* read.c (emit_leb128_expr): Extended unsigned big number for
+	sleb128.
+	* testsuite/gas/all/gas.exp (test_cond): Add sleb128-8 test.
+	* testsuite/gas/all/sleb128.d: New test.
+	* testsuite/gas/all/sleb128.s: New test source.
+
 2017-01-09  Nick Clifton  <nickc@redhat.com>
 
 	* po/sv.po: New Swedish translation.
diff --git a/gas/read.c b/gas/read.c
index 5c0d320..3669b28 100644
--- a/gas/read.c
+++ b/gas/read.c
@@ -5344,13 +5344,21 @@ emit_leb128_expr (expressionS *exp, int sign)
   else if (op == O_big)
     {
       /* O_big is a different sort of constant.  */
-
+      int nbr_digits = exp->X_add_number;
       unsigned int size;
       char *p;
 
-      size = output_big_leb128 (NULL, generic_bignum, exp->X_add_number, sign);
+      /* If the leading littenum is 0xffff, prepend a 0 to avoid confusion with
+	 a signed number.  Unary operators like - or ~ always extend the
+	 bignum to its largest size.  */
+      if (exp->X_unsigned
+	  && nbr_digits < SIZE_OF_LARGE_NUMBER
+	  && generic_bignum[nbr_digits - 1] == LITTLENUM_MASK)
+	generic_bignum[nbr_digits++] = 0;
+
+      size = output_big_leb128 (NULL, generic_bignum, nbr_digits, sign);
       p = frag_more (size);
-      if (output_big_leb128 (p, generic_bignum, exp->X_add_number, sign) > size)
+      if (output_big_leb128 (p, generic_bignum, nbr_digits, sign) > size)
 	abort ();
     }
   else
diff --git a/gas/testsuite/gas/all/gas.exp b/gas/testsuite/gas/all/gas.exp
index 8f97ed8..6b5aec0 100644
--- a/gas/testsuite/gas/all/gas.exp
+++ b/gas/testsuite/gas/all/gas.exp
@@ -393,6 +393,7 @@ run_dump_test sleb128-5
 if { ![istarget "tic4x*-*-*"] && ![istarget "tic54x*-*-*"] } {
     run_dump_test sleb128-7
 }
+run_dump_test sleb128-8
 
 # .byte is 32 bits on tic4x, and .p2align isn't supported on tic54x
 # .space is different on hppa*-hpux.
diff --git a/gas/testsuite/gas/all/sleb128-8.d b/gas/testsuite/gas/all/sleb128-8.d
new file mode 100644
index 0000000..793337c
--- /dev/null
+++ b/gas/testsuite/gas/all/sleb128-8.d
@@ -0,0 +1,7 @@
+#objdump : -s -j .data -j "\$DATA\$"
+#name : .sleb128 tests (8)
+
+.*: .*
+
+Contents of section (\.data|\$DATA\$):
+ 0000 ffffffff ffff3f .*
diff --git a/gas/testsuite/gas/all/sleb128-8.s b/gas/testsuite/gas/all/sleb128-8.s
new file mode 100644
index 0000000..ab3e785
--- /dev/null
+++ b/gas/testsuite/gas/all/sleb128-8.s
@@ -0,0 +1,2 @@
+	.data
+	.sleb128 281474976710655