Relative expressions and ASSERT

[H.J. Lu]

On Thu, Dec 16, 2010 at 4:01 PM, Alan Modra <amodra@gmail.com> wrote:
> On Thu, Dec 16, 2010 at 03:14:38PM -0800, H.J. Lu wrote:
>> Your patch doesn't work. I got
>>
>> ./ld: kernel image bigger than KERNEL_IMAGE_SIZE
>>
>> due to arch/x86/kernel/vmlinux.lds:
>>
>> ----
>> /*
>>  * Build-time check on the image size:
>>  */
>> . = ASSERT((_end - _text <= (512 * 1024 * 1024)),
>>     "kernel image bigger than KERNEL_IMAGE_SIZE");
>
> Extracting the relevant parts from the kernel link script:
>
> SECTIONS
> {
>  . = 0xc000;
>  .text :
>  {
>    _text = .;
>    *(.text)
>  }
>  _end = .;
> }
> ASSERT (_end - _text <= 0x100, "fail");
>
> You'd think that under the new rules, this ought to work.  "_end" is
> an absolute address, so when evaluating "_end - _text", "_text" ought
> to be converted from relative to absolute, the subtraction resuling in
> an absolute address.  Then 0x100 gets converted from a number to
> absolute address before being compared.
>
> The trouble is that "_end" is *not* treated as an absolute address but
> as a plain number.  That makes ld convert "_end" to a .text relative
> address when evaluation "_end - _text", which doesn't cause a problem
> at that stage, but the result is a relative address.  That means 0x100
> is converted to a .text relative address too, which gives the wrong
> result.
>
> The underlying problem is that we don't distinguish between plain
> numbers and absolute addresses once values are stored in symbols.
>

I am putting this into the Linux binutils.


-- 
H.J.
---
ld/

2010-12-16  H.J. Lu  <hongjiu.lu@intel.com>

	PR ld/12327
	* ldexp.c (exp_fold_tree_1): Only make absolute symbol value
	absolute.

ld/testsuite/

2010-12-16  H.J. Lu  <hongjiu.lu@intel.com>

	PR ld/12327
	* ld-scripts/defined.exp: Run defined4.

	* ld-scripts/defined4.d: New.
	* ld-scripts/defined4.s: Likewise.
	* ld-scripts/defined4.t: Likewise.
-------------- next part --------------
ld/

2010-12-16  H.J. Lu  <hongjiu.lu@intel.com>

	PR ld/12327
	* ldexp.c (exp_fold_tree_1): Only make absolute symbol value
	absolute.

ld/testsuite/

2010-12-16  H.J. Lu  <hongjiu.lu@intel.com>

	PR ld/12327
	* ld-scripts/defined.exp: Run defined4.

	* ld-scripts/defined4.d: New.
	* ld-scripts/defined4.s: Likewise.
	* ld-scripts/defined4.t: Likewise.

diff --git a/ld/ldexp.c b/ld/ldexp.c
index de7f9f2..c8fa331 100644
--- a/ld/ldexp.c
+++ b/ld/ldexp.c
@@ -691,12 +691,15 @@ fold_name (etree_type *tree)
 static void
 exp_fold_tree_1 (etree_type *tree)
 {
+  bfd_boolean absolute;
+
   if (tree == NULL)
     {
       memset (&expld.result, 0, sizeof (expld.result));
       return;
     }
 
+  absolute = TRUE;
   switch (tree->type.node_class)
     {
     case etree_value:
@@ -851,6 +854,21 @@ exp_fold_tree_1 (etree_type *tree)
 
     case etree_name:
       fold_name (tree);
+      if (tree->name.name
+	  && tree->name.name[0] != '.'
+	  && tree->name.name[1] != '\0'
+	  && link_info.hash)
+	{
+	  struct bfd_link_hash_entry *h;
+
+	  /* Only make absolute symbol value absolute.  */
+	  h = bfd_link_hash_lookup (link_info.hash, tree->name.name,
+				    FALSE, FALSE, TRUE);
+	  if (h
+	      && (h->type == bfd_link_hash_defined
+		  || h->type == bfd_link_hash_defweak))
+	    absolute = (h->u.def.section == bfd_abs_section_ptr);
+	}
       break;
 
     default:
@@ -861,7 +879,8 @@ exp_fold_tree_1 (etree_type *tree)
 
   /* Any value not inside an output section statement is an
      absolute value.  */
-  if (expld.result.valid_p
+  if (absolute
+      && expld.result.valid_p
       && expld.section == bfd_abs_section_ptr)
     make_abs ();
 }
diff --git a/ld/testsuite/ld-scripts/defined.exp b/ld/testsuite/ld-scripts/defined.exp
index 15cc079..5742ae9 100644
--- a/ld/testsuite/ld-scripts/defined.exp
+++ b/ld/testsuite/ld-scripts/defined.exp
@@ -66,4 +66,5 @@ if ![ld_simple_link $ld tmpdir/def "$LDFLAGS -T $srcdir/$subdir/defined.t tmpdir
 set prms_id 0
 run_dump_test "defined2"
 run_dump_test "defined3"
+run_dump_test "defined4"
 set LDFLAGS "$saved_LDFLAGS"
--- /dev/null	2010-12-14 15:22:59.420000000 -0800
+++ binutils/ld/testsuite/ld-scripts/defined4.d	2010-12-16 14:00:46.264217155 -0800
@@ -0,0 +1,10 @@
+#ld: -Tdefined4.t
+#nm: -B
+#source: defined4.s
+
+# Check that arithmetic on DEFINED works.
+#...
+0+0 D defined
+#...
+0+0 D defined1
+#pass
--- /dev/null	2010-12-14 15:22:59.420000000 -0800
+++ binutils/ld/testsuite/ld-scripts/defined4.s	2010-12-16 12:46:23.558273203 -0800
@@ -0,0 +1,4 @@
+	.globl	defined
+	.data
+defined:
+	.word 0
--- /dev/null	2010-12-14 15:22:59.420000000 -0800
+++ binutils/ld/testsuite/ld-scripts/defined4.t	2010-12-16 12:46:45.236797081 -0800
@@ -0,0 +1,6 @@
+SECTIONS {
+	.text : { *(.text) }
+	.data : { *(.data) }
+	.bss : { *(.bss) *(COMMON) }
+}
+defined1 = defined;