[binutils-gdb] [gdb/symtab] Prefer def over decl (inter-CU case)

[binutils-gdb] [gdb/symtab] Prefer def over decl (inter-CU case)

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=de82891ce5b6d2c8109f512cd0732325f4cd0557

commit de82891ce5b6d2c8109f512cd0732325f4cd0557
Author: Tom de Vries <tdevries@suse.de>
Date:   Thu Apr 23 15:42:47 2020 +0200

    [gdb/symtab] Prefer def over decl (inter-CU case)
    
    When running test-case gdb.threads/tls.exp with target board -readnow, we
    have:
    ...
    (gdb) print a_thread_local^M
    Cannot find thread-local storage for process 0, executable file tls/tls:^M
    Cannot find thread-local variables on this target^M
    (gdb) FAIL: gdb.threads/tls.exp: print a_thread_local
    ...
    while with native we have:
    ...
    (gdb) print a_thread_local^M
    Cannot read `a_thread_local' without registers^M
    (gdb) PASS: gdb.threads/tls.exp: print a_thread_local
    ...
    
    The difference in behaviour can be explained as follows.  Without -readnow, we
    have two a_thread_locals, the def and the decl, each in a different CU:
    ...
    $ gdb -batch outputs/gdb.threads/tls/tls \
        -ex "maint expand-symtabs" \
        -ex "print a_thread_local" \
        -ex "maint print symbols" \
        | grep "a_thread_local;"
    Cannot read `a_thread_local' without registers
     int a_thread_local; computed at runtime
     int a_thread_local; unresolved
    ...
    and with -readnow, we have the opposite order:
    ...
    $ gdb -readnow -batch outputs/gdb.threads/tls/tls  \
        -ex "maint expand-symtabs" \
        -ex "print a_thread_local" \
        -ex "maint print symbols" \
        | grep "a_thread_local;"
    Cannot find thread-local storage for process 0, executable file tls/tls:
    Cannot find thread-local variables on this target
     int a_thread_local; unresolved
     int a_thread_local; computed at runtime
    ...
    
    Fix the FAIL by preferring the def over the decl (something we already do
    intra-CU since the fix for PR24971, commit 93e55f0a03 "[gdb/symtab] Prefer var
    def over decl").
    
    Build and reg-tested on x86_64-linux.
    
    gdb/ChangeLog:
    
    2020-04-23  Tom de Vries  <tdevries@suse.de>
    
            PR symtab/25807
            * block.c (best_symbol, better_symbol): Promote to external.
            * block.h (best_symbol, better_symbol): Declare.
            * symtab.c (lookup_symbol_in_objfile_symtabs): Prefer def over
            decl.
    
    gdb/testsuite/ChangeLog:
    
    2020-04-23  Tom de Vries  <tdevries@suse.de>
    
            * gdb.base/decl-before-def-decl.c: New test.
            * gdb.base/decl-before-def-def.c: New test.
            * gdb.base/decl-before-def.exp: New file.

Diff:
---
 gdb/ChangeLog                                 |  8 +++++++
 gdb/block.c                                   |  9 ++++---
 gdb/block.h                                   | 10 ++++++++
 gdb/symtab.c                                  | 34 +++++++++++++++++++++------
 gdb/testsuite/ChangeLog                       |  6 +++++
 gdb/testsuite/gdb.base/decl-before-def-decl.c | 25 ++++++++++++++++++++
 gdb/testsuite/gdb.base/decl-before-def-def.c  | 18 ++++++++++++++
 gdb/testsuite/gdb.base/decl-before-def.exp    | 26 ++++++++++++++++++++
 8 files changed, 124 insertions(+), 12 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index cbe26937198..f1ebf09ff46 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2020-04-23  Tom de Vries  <tdevries@suse.de>
+
+	PR symtab/25807
+	* block.c (best_symbol, better_symbol): Promote to external.
+	* block.h (best_symbol, better_symbol): Declare.
+	* symtab.c (lookup_symbol_in_objfile_symtabs): Prefer def over
+	decl.
+
 2020-04-23  Tom Tromey  <tromey@adacore.com>
 
 	PR ada/25837:
diff --git a/gdb/block.c b/gdb/block.c
index 9b582433e48..597d6d5d875 100644
--- a/gdb/block.c
+++ b/gdb/block.c
@@ -657,19 +657,18 @@ block_iter_match_next (const lookup_name_info &name,
   return block_iter_match_step (iterator, name, 0);
 }
 
-/* Return true if symbol A is the best match possible for DOMAIN.  */
+/* See block.h.  */
 
-static bool
+bool
 best_symbol (struct symbol *a, const domain_enum domain)
 {
   return (SYMBOL_DOMAIN (a) == domain
 	  && SYMBOL_CLASS (a) != LOC_UNRESOLVED);
 }
 
-/* Return symbol B if it is a better match than symbol A for DOMAIN.
-   Otherwise return A.  */
+/* See block.h.  */
 
-static struct symbol *
+struct symbol *
 better_symbol (struct symbol *a, struct symbol *b, const domain_enum domain)
 {
   if (a == NULL)
diff --git a/gdb/block.h b/gdb/block.h
index 7c0b2d36966..50ab049f8e6 100644
--- a/gdb/block.h
+++ b/gdb/block.h
@@ -342,6 +342,16 @@ extern struct symbol *block_iter_match_first (const struct block *block,
 extern struct symbol *block_iter_match_next
   (const lookup_name_info &name, struct block_iterator *iterator);
 
+/* Return true if symbol A is the best match possible for DOMAIN.  */
+
+extern bool best_symbol (struct symbol *a, const domain_enum domain);
+
+/* Return symbol B if it is a better match than symbol A for DOMAIN.
+   Otherwise return A.  */
+
+extern struct symbol *better_symbol (struct symbol *a, struct symbol *b,
+				     const domain_enum domain);
+
 /* Search BLOCK for symbol NAME in DOMAIN.  */
 
 extern struct symbol *block_lookup_symbol (const struct block *block,
diff --git a/gdb/symtab.c b/gdb/symtab.c
index dc079efbc27..1eef97837e8 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -2285,6 +2285,8 @@ lookup_symbol_in_objfile_symtabs (struct objfile *objfile,
 			  name, domain_name (domain));
     }
 
+  struct block_symbol other;
+  other.symbol = NULL;
   for (compunit_symtab *cust : objfile->compunits ())
     {
       const struct blockvector *bv;
@@ -2295,18 +2297,36 @@ lookup_symbol_in_objfile_symtabs (struct objfile *objfile,
       block = BLOCKVECTOR_BLOCK (bv, block_index);
       result.symbol = block_lookup_symbol_primary (block, name, domain);
       result.block = block;
-      if (result.symbol != NULL)
+      if (result.symbol == NULL)
+	continue;
+      if (best_symbol (result.symbol, domain))
 	{
-	  if (symbol_lookup_debug > 1)
+	  other = result;
+	  break;
+	}
+      if (symbol_matches_domain (result.symbol->language (),
+				 SYMBOL_DOMAIN (result.symbol), domain))
+	{
+	  struct symbol *better
+	    = better_symbol (other.symbol, result.symbol, domain);
+	  if (better != other.symbol)
 	    {
-	      fprintf_unfiltered (gdb_stdlog, " = %s (block %s)\n",
-				  host_address_to_string (result.symbol),
-				  host_address_to_string (block));
+	      other.symbol = better;
+	      other.block = block;
 	    }
-	  result.symbol = fixup_symbol_section (result.symbol, objfile);
-	  return result;
+	}
+    }
 
+  if (other.symbol != NULL)
+    {
+      if (symbol_lookup_debug > 1)
+	{
+	  fprintf_unfiltered (gdb_stdlog, " = %s (block %s)\n",
+			      host_address_to_string (other.symbol),
+			      host_address_to_string (other.block));
 	}
+      other.symbol = fixup_symbol_section (other.symbol, objfile);
+      return other;
     }
 
   if (symbol_lookup_debug > 1)
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 7e6bf73fa41..e37aca2b5af 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-23  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.base/decl-before-def-decl.c: New test.
+	* gdb.base/decl-before-def-def.c: New test.
+	* gdb.base/decl-before-def.exp: New file.
+
 2020-04-23  Tom de Vries  <tdevries@suse.de>
 
 	* gdb.base/readnever.exp: Skip if GDBFLAGS contain -readnow/--readnow.
diff --git a/gdb/testsuite/gdb.base/decl-before-def-decl.c b/gdb/testsuite/gdb.base/decl-before-def-decl.c
new file mode 100644
index 00000000000..3e4e6d777d9
--- /dev/null
+++ b/gdb/testsuite/gdb.base/decl-before-def-decl.c
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+extern int a[];
+
+int
+main (void)
+{
+  a[0] = 1;
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/decl-before-def-def.c b/gdb/testsuite/gdb.base/decl-before-def-def.c
new file mode 100644
index 00000000000..4d25248bc27
--- /dev/null
+++ b/gdb/testsuite/gdb.base/decl-before-def-def.c
@@ -0,0 +1,18 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int a[2] = { 1, 2 };
diff --git a/gdb/testsuite/gdb.base/decl-before-def.exp b/gdb/testsuite/gdb.base/decl-before-def.exp
new file mode 100644
index 00000000000..feb2084a82f
--- /dev/null
+++ b/gdb/testsuite/gdb.base/decl-before-def.exp
@@ -0,0 +1,26 @@
+# Copyright 2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+standard_testfile decl-before-def-decl.c decl-before-def-def.c
+set sources [list $srcfile $srcfile2]
+
+if {[prepare_for_testing "failed to prepare" $testfile $sources]} {
+    return -1
+}
+
+# This is required due to PR25764.
+gdb_test "maint expand-symtabs"
+
+gdb_test "p a" { = \{1, 2\}}