Re: [patch] Re: Advice on fixing gdb/12528

[Paul Pluzhnikov <ppluzhnikov@google.com>]

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On Mon, Mar 14, 2011 at 5:41 PM, Jan Kratochvil
<jan.kratochvil@redhat.com> wrote:
> On Mon, 14 Mar 2011 22:01:44 +0100, Paul Pluzhnikov wrote:
>> --- /dev/null 1 Jan 1970 00:00:00 -0000
>> +++ testsuite/gdb.cp/pr12528.exp      14 Mar 2011 20:52:11 -0000
>
> I would prefer any non-numeric name of the testfile.

How does "break-on-linker-gcd-function.exp" sound?

>> +set additional_flags {-ffunction-sections -Wl,--gc-sections}
>> +if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable \
>> +        [list debug c++ additional_flags=$additional_flags]] != "" } {
>> +    untested $srcfile
>> +    return -1
>> +}
>
> This testfile correctly breaks without the fix applied with:
>        g++ (GCC) 4.4.6 20110314 (prerelease)
>
> but it gives false PASS even without the fix applied with:
>        g++ (GCC) 4.5.3 20110314 (prerelease)
>        g++ (GCC) 4.6.0 20110312 (experimental)
>
> as recent GCCs no longer create multiple ctors in such case.

Yes: I noted that in gdb/12568.

I am not sure how I can trigger the bug with newer GCC versions...
Ah yes, I can.

> For a real testcase it should be in gdb.dwarf2/ (and then the special
> compilation options are sure no longer needed).

Sorry, I didn't follow that part. Why special options wouldn't be needed?

>> +if { ![runto_main] } {
>> +    fail "Can't run to main"
>> +    return
>> +}
>
> It could check the `info break' output without running the testcase at all.

Done.

Thanks,
-- 
Paul Pluzhnikov


ChangeLog:

2011-03-14  Paul Pluzhnikov  <ppluzhnikov@google.com>

       PR gdb/12528
       * dwarf2read.c (noop_record_line): New function.
       (dwarf_decode_lines): Ignore line tables for GCd functions.

testsuite/ChangeLog:

2011-03-14  Paul Pluzhnikov  <ppluzhnikov@google.com>

       PR gdb/12528
       * gdb.dwarf2/break-on-linker-gcd-function.exp: New test.
       * gdb.dwarf2/break-on-linker-gcd-function.cc: New file.

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Index: dwarf2read.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2read.c,v
retrieving revision 1.508
diff -u -p -p -u -r1.508 dwarf2read.c
--- dwarf2read.c	9 Mar 2011 07:07:55 -0000	1.508
+++ dwarf2read.c	15 Mar 2011 01:38:16 -0000
@@ -10341,6 +10341,14 @@ psymtab_include_file_name (const struct 
   return include_name;
 }
 
+/* Ignore this record_line request.  */
+
+static void
+noop_record_line (struct subfile *subfile, int line, CORE_ADDR pc)
+{
+  return;
+}
+
 /* Decode the Line Number Program (LNP) for the given line_header
    structure and CU.  The actual information extracted and the type
    of structures created from the LNP depends on the value of PST.
@@ -10376,6 +10384,8 @@ dwarf_decode_lines (struct line_header *
   struct gdbarch *gdbarch = get_objfile_arch (objfile);
   const int decode_for_pst_p = (pst != NULL);
   struct subfile *last_subfile = NULL, *first_subfile = current_subfile;
+  void (*p_record_line) (struct subfile *subfile, int line, CORE_ADDR pc)
+    = record_line;
 
   baseaddr = ANOFFSET (objfile->section_offsets, SECT_OFF_TEXT (objfile));
 
@@ -10445,13 +10455,13 @@ dwarf_decode_lines (struct line_header *
 			{
 			  addr = gdbarch_addr_bits_remove (gdbarch, address);
 			  if (last_subfile)
-			    record_line (last_subfile, 0, addr);
+			    (*p_record_line) (last_subfile, 0, addr);
 			  last_subfile = current_subfile;
 			}
 		      /* Append row to matrix using current values.  */
 		      addr = check_cu_functions (address, cu);
 		      addr = gdbarch_addr_bits_remove (gdbarch, addr);
-		      record_line (current_subfile, line, addr);
+		      (*p_record_line) (current_subfile, line, addr);
 		    }
 		}
 	      basic_block = 0;
@@ -10468,12 +10478,19 @@ dwarf_decode_lines (struct line_header *
 	      switch (extended_op)
 		{
 		case DW_LNE_end_sequence:
+		  p_record_line = record_line;
 		  end_sequence = 1;
 		  break;
 		case DW_LNE_set_address:
 		  address = read_address (abfd, line_ptr, cu, &bytes_read);
 		  op_index = 0;
 		  line_ptr += bytes_read;
+
+		  if (address == 0 && !dwarf2_per_objfile->has_section_at_zero)
+		    /* This line table is for a function which has been
+		       GCd by the linker.  Ignore it.  PR gdb/12528 */
+		    p_record_line = noop_record_line;
+
 		  address += baseaddr;
 		  break;
 		case DW_LNE_define_file:
@@ -10528,12 +10545,12 @@ dwarf_decode_lines (struct line_header *
 			{
 			  addr = gdbarch_addr_bits_remove (gdbarch, address);
 			  if (last_subfile)
-			    record_line (last_subfile, 0, addr);
+			    (*p_record_line) (last_subfile, 0, addr);
 			  last_subfile = current_subfile;
 			}
 		      addr = check_cu_functions (address, cu);
 		      addr = gdbarch_addr_bits_remove (gdbarch, addr);
-		      record_line (current_subfile, line, addr);
+		      (*p_record_line) (current_subfile, line, addr);
 		    }
 		}
 	      basic_block = 0;
@@ -10632,7 +10649,7 @@ dwarf_decode_lines (struct line_header *
           if (!decode_for_pst_p)
 	    {
 	      addr = gdbarch_addr_bits_remove (gdbarch, address);
-	      record_line (current_subfile, 0, addr);
+	      (*p_record_line) (current_subfile, 0, addr);
 	    }
         }
     }
Index: testsuite/gdb.dwarf2/break-on-linker-gcd-function.exp
===================================================================
RCS file: testsuite/gdb.dwarf2/break-on-linker-gcd-function.exp
diff -N testsuite/gdb.dwarf2/break-on-linker-gcd-function.exp
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.dwarf2/break-on-linker-gcd-function.exp	15 Mar 2011 01:38:16 -0000
@@ -0,0 +1,51 @@
+# Copyright 2011 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/>.
+
+# This file is part of the gdb testsuite
+
+# Test casting, especially between class types or pointer-to-class
+# types.
+
+# This file is part of the gdb testsuite
+
+if $tracelevel then {
+    strace $tracelevel
+}
+
+#
+# test running programs
+#
+if { [skip_cplus_tests] } { continue }
+
+set testfile "break-on-linker-gcd-function"
+set srcfile ${testfile}.cc
+set binfile ${objdir}/${subdir}/${testfile}
+
+if [get_compiler_info ${binfile} "c++"] {
+    return -1;
+}
+
+set additional_flags {-ffunction-sections -Wl,--gc-sections}
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable \
+	   [list debug c++ additional_flags=$additional_flags]] != "" } {
+    untested $srcfile
+    return -1
+}
+
+clean_restart $testfile
+
+# This accepts e.g. "Breakpoint 1 at 0x40968a" (fixed GDB)
+# but rejects e.g. "Breakpoint 1 at 0x4" (broken GDB).
+gdb_test "b [gdb_get_line_number "gdb break here"]" "Breakpoint \[0-9\] at 0x\[0-9a-f\]\[0-9a-f\]+: .*"
Index: testsuite/gdb.dwarf2/break-on-linker-gcd-function.cc
===================================================================
RCS file: testsuite/gdb.dwarf2/break-on-linker-gcd-function.cc
diff -N testsuite/gdb.dwarf2/break-on-linker-gcd-function.cc
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.dwarf2/break-on-linker-gcd-function.cc	15 Mar 2011 01:38:16 -0000
@@ -0,0 +1,32 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2011 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/>.
+   */
+
+// Test case for PR gdb/12528
+
+void
+foo ()
+{
+  // This function is not referenced and should be GCd by the linker
+  return; // gdb break here
+}
+
+int
+main ()
+{
+  return 0;
+}