Re: [PATCH 2/2] ld: Don't evaluate unneeded PROVIDE expressions.

[Andrew Burgess <andrew dot burgess at embecosm dot com>]

* Alan Modra <amodra@gmail.com> [2015-01-12 11:08:53 +1030]:

> > ld/testsuite/ChangeLog:
> >
> > 	* ld-scripts/provide-4.d: New file.
> > 	* ld-scripts/provide-4-map.d: New file.
> > 	* ld-scripts/provide-4.t: New file.
> > 	* ld-scripts/provide.exp: Run the provide-4.d test.
>
> This part isn't OK yet.  You need to make sure new tests pass on more
> than just Linux x86.

Alan,

Thanks for taking the time to review my patch, and I'm sorry that the
change wasn't up to standard.

I've updated the expected results, and tested against the same set of
builds you suggest, I'm now seeing passes on all but 3 builds, and
these 3 failures are, I believe, not related to my changes.

I could look to XFAIL my new test for those targets, but the same
targets are FAIL-ing other tests from the 'provide.exp' file, it's
your call.

The 3 misbehaving builds are alpha-dec-vms, powerpcle-cygwin, and
tic54x-coff.  It is quite possible that I've not configured or built
these targets correctly, I have no experience with any of these.

Revised patch is below, the only change is to the testsuite directory.

Thanks again,
Andrew

---
When creating a linker mapfile (using -Map=MAPFILE), we previously would
always try to evaluate the expression from a PROVIDE statement.

However, this is not always safe, consider:

  PROVIDE (foo = 0x10);
  PROVIDE (bar = foo);

In this example, if neither 'foo' or 'bar' is needed, then while
generating the linker mapfile evaluating the expression for 'foo' is
harmless (just the value 0x10).  However, evaluating the expression for
'bar' requires the symbol 'foo', which is undefined.  This used to cause
a fatal error.

This patch changes the behaviour, so that when the destination of the
PROVIDE is not defined (that is the PROVIDE is not going to provide
anything) the expression is not evaluated, and instead a special string
is displayed to indicate that the linker is discarding the PROVIDE
statement.

This change not only fixes the spurious undefined symbol error, but also
means that a user can now tell if a PROVIDE statement has provided
anything by inspecting the linker mapfile, something that could not be
done before.

ld/ChangeLog:

	* ldlang.c (print_assignment): Only evaluate the expression for a
	PROVIDE'd assignment when the destination is being defined.
	Display a special message for PROVIDE'd symbols that are not being
	provided.

ld/testsuite/ChangeLog:

	* ld-scripts/provide-4.d: New file.
	* ld-scripts/provide-4-map.d: New file.
	* ld-scripts/provide-4.t: New file.
	* ld-scripts/provide.exp: Run the provide-4.d test.
---
 ld/ChangeLog                            |  7 +++++++
 ld/ldlang.c                             | 14 ++++++++++++--
 ld/testsuite/ChangeLog                  |  7 +++++++
 ld/testsuite/ld-scripts/provide-4-map.d | 13 +++++++++++++
 ld/testsuite/ld-scripts/provide-4.d     |  9 +++++++++
 ld/testsuite/ld-scripts/provide-4.t     | 16 ++++++++++++++++
 ld/testsuite/ld-scripts/provide.exp     |  1 +
 7 files changed, 65 insertions(+), 2 deletions(-)
 create mode 100644 ld/testsuite/ld-scripts/provide-4-map.d
 create mode 100644 ld/testsuite/ld-scripts/provide-4.d
 create mode 100644 ld/testsuite/ld-scripts/provide-4.t

diff --git a/ld/ChangeLog b/ld/ChangeLog
index be4617f..fab597e 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,10 @@
+2015-01-07  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* ldlang.c (print_assignment): Only evaluate the expression for a
+	PROVIDE'd assignment when the destination is being defined.
+	Display a special message for PROVIDE'd symbols that are not being
+	provided.
+
 2015-01-01  Alan Modra  <amodra@gmail.com>
 
 	* ldver.c (ldversion): Just print current year.
diff --git a/ld/ldlang.c b/ld/ldlang.c
index 9f3d209..a99febe 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -3983,7 +3983,14 @@ print_assignment (lang_assignment_statement_type *assignment,
   osec = output_section->bfd_section;
   if (osec == NULL)
     osec = bfd_abs_section_ptr;
-  exp_fold_tree (tree, osec, &print_dot);
+
+  if (assignment->exp->type.node_class != etree_provide
+      || bfd_link_hash_lookup (link_info.hash,
+                               assignment->exp->assign.dst,
+                               FALSE, FALSE, TRUE) != NULL)
+    exp_fold_tree (tree, osec, &print_dot);
+  else
+    expld.result.valid_p = FALSE;
   if (expld.result.valid_p)
     {
       bfd_vma value;
@@ -4021,7 +4028,10 @@ print_assignment (lang_assignment_statement_type *assignment,
     }
   else
     {
-      minfo ("*undef*   ");
+      if (assignment->exp->type.node_class == etree_provide)
+        minfo ("[!provide]");
+      else
+        minfo ("*undef*   ");
 #ifdef BFD64
       minfo ("        ");
 #endif
diff --git a/ld/testsuite/ChangeLog b/ld/testsuite/ChangeLog
index 266e996..521c819 100644
--- a/ld/testsuite/ChangeLog
+++ b/ld/testsuite/ChangeLog
@@ -1,5 +1,12 @@
 2015-01-07  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* ld-scripts/provide-4.d: New file.
+	* ld-scripts/provide-4-map.d: New file.
+	* ld-scripts/provide-4.t: New file.
+	* ld-scripts/provide.exp: Run the provide-4.d test.
+
+2015-01-07  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* ld-scripts/overlay-size.d: Add 'map' option.
 	* ld-scripts/overlay-size.exp: Remove manual check of mapfile.
 	* lib/ld-lib.exp (run_dump_test): Add support for new 'map'
diff --git a/ld/testsuite/ld-scripts/provide-4-map.d b/ld/testsuite/ld-scripts/provide-4-map.d
new file mode 100644
index 0000000..59c84b5
--- /dev/null
+++ b/ld/testsuite/ld-scripts/provide-4-map.d
@@ -0,0 +1,13 @@
+#...
+Linker script and memory map
+#...
+                0x0+1                PROVIDE \(foo, 0x1\)
+                \[!provide\]                        PROVIDE \(bar, 0x2\)
+                0x0+3                PROVIDE \(baz, 0x3\)
+#...
+                0x0+2000                foo
+                \[!provide\]                        PROVIDE \(loc1, ALIGN \(\., 0x10\)\)
+                0x0+2010                PROVIDE \(loc2, ALIGN \(\., 0x10\)\)
+                \[!provide\]                        PROVIDE \(loc3, \(loc1 \+ 0x20\)\)
+                0x0+2030                loc4 = \(loc2 \+ 0x20\)
+#...
diff --git a/ld/testsuite/ld-scripts/provide-4.d b/ld/testsuite/ld-scripts/provide-4.d
new file mode 100644
index 0000000..a7d37e3
--- /dev/null
+++ b/ld/testsuite/ld-scripts/provide-4.d
@@ -0,0 +1,9 @@
+#source: provide-2.s
+#ld: -T provide-4.t
+#PROG: nm
+#map: provide-4-map.d
+#...
+0+3 A baz
+0+2000 D foo
+0+2010 D loc2
+0+2030 A loc4
diff --git a/ld/testsuite/ld-scripts/provide-4.t b/ld/testsuite/ld-scripts/provide-4.t
new file mode 100644
index 0000000..424c238
--- /dev/null
+++ b/ld/testsuite/ld-scripts/provide-4.t
@@ -0,0 +1,16 @@
+SECTIONS
+{
+  PROVIDE (foo = 1);
+  PROVIDE (bar = 2);
+  PROVIDE (baz = 3);
+  .data 0x2000 :
+  {
+    *(.data)
+
+    PROVIDE (loc1 = ALIGN (., 0x10));
+    PROVIDE (loc2 = ALIGN (., 0x10));
+  }
+
+  PROVIDE (loc3 = loc1 + 0x20);
+  loc4 = loc2 + 0x20;
+}
diff --git a/ld/testsuite/ld-scripts/provide.exp b/ld/testsuite/ld-scripts/provide.exp
index 7f45e58..baba0a4 100644
--- a/ld/testsuite/ld-scripts/provide.exp
+++ b/ld/testsuite/ld-scripts/provide.exp
@@ -40,5 +40,6 @@ run_dump_test provide-1
 run_dump_test provide-2
 setup_xfail *-*-*
 run_dump_test provide-3
+run_dump_test provide-4
 
 set LDFLAGS "$saved_LDFLAGS"
-- 
1.9.3