Patch: DWARF2 location lists vs. shared libraries

Bryce McKinlay
2004-05-05T00:45:54Z

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GDB has been having problems debugging shared libraries built with CVS
gcc @ -O2. For example, libgcj backtraces look like this:

(gdb) bt
#0 _Jv_FindClass (name=0x83ebfe0, loader=Variable "loader" is not
available.
) at ../../../libjava/java/lang/natClassLoader.cc:375
#1 0x01442a99 in _Jv_FindClassFromSignature (sig=Variable "sig" is not
available.
) at ../../../libjava/prims.cc:753
#2 0x01442acb in _Jv_FindClassFromSignature (sig=Variable "sig" is not
available.
) at ../../../libjava/prims.cc:757
#3 0x01467d61 in _Jv_PrepareCompiledClass (klass=0x18f3500) at
../../../libjava/java/lang/natClassLoader.cc:107
#4 0x014670b8 in java::lang::Class::initializeClass (this=Variable
"this" is not available.
) at ../../../libjava/java/lang/natClass.cc:733

The problem seems to be that dwarf2read.c does not offset
dwarf2_loclist_baton's base_address for shared library load addresses.
This means that find_location_expression() fails, since the unrelocated
base_address in the baton does not match up with the PC being searched for.

Please review and commit. Since this bug means debugging of -O2 shared
libraries with cvs GCC is basically broken, perhaps the fix should go on
the stable branch as well?

Thanks to Daniel Berlin for helping to track this down!

Bryce

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2004-05-04 Bryce McKinlay <mckinlay@redhat.com>

* dwarf2read.c (dwarf2_symbol_mark_computed): Use ANOFFSET to
adjust baton's base_address for shared libraries.

Index: dwarf2read.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2read.c,v
retrieving revision 1.150
diff -u -r1.150 dwarf2read.c
--- dwarf2read.c 4 May 2004 00:11:25 -0000 1.150
+++ dwarf2read.c 5 May 2004 00:41:00 -0000
@@ -8662,6 +8662,7 @@
if (attr->form == DW_FORM_data4 || attr->form == DW_FORM_data8)
{
struct dwarf2_loclist_baton *baton;
+ CORE_ADDR base_offset;

baton = obstack_alloc (&cu->objfile->objfile_obstack,
sizeof (struct dwarf2_loclist_baton));
@@ -8671,7 +8672,10 @@
don't run off the edge of the section. */
baton->size = dwarf2_per_objfile->loc_size - DW_UNSND (attr);
baton->data = dwarf2_per_objfile->loc_buffer + DW_UNSND (attr);
- baton->base_address = cu->header.base_address;
+ /* Set base_address, adjusting for shared libraries. */
+ base_offset = ANOFFSET (cu->objfile->section_offsets,
+ SECT_OFF_TEXT (cu->objfile));
+ baton->base_address = cu->header.base_address + base_offset;
if (cu->header.base_known == 0)
complaint (&symfile_complaints,
"Location list used without specifying the CU base address.");