On 17/03/10 22:50, Walter Bright wrote:
grauzone wrote:
dmd producing buggy debugging information seems to be an old problem:
http://d.puremagic.com/issues/show_bug.cgi?id=1079
The problem is that dmd produces dwarf debug info according to the dwarf
spec. When gdb fails, I have no clue why, and nobody has ever been able
to figure out just *what* in the dwarf info is causing gdb to fail.
Some problems were identified a few months back, and those were fixed
(evidently gdb cannot handle module records, and gdb also relied on some
undocumented stuff).
If anyone wants to peruse the gdb source and figure out exactly *what*
it is choking on, that would be most appreciated.
I've spent about half an hour trying to track this down, and I can't
seem to reproduce the problem. The only time I can get the errors
mentioned here and in the listed bug is when using -g. When switching to
-gc the problems disappear. Does anyone have a test case that fails with
-gc too that I can play with?
The reason this happens when using -g is the D extensions to dwarf which
GDB doesn't support (even with the gdb-patches applied) are used here,
which causes the error, as gdb is unable to parse the debug info. When
using -gc, dmd doesn't use the D extensions, so the error doesn't occur.
To fix this, gdb would need patching to add support for the D
extensions, or alternatively we'll have to keep using -gc.
----
void main()
{
char[] foo;
foo ~= 'a';
}
----
When compiled using -gc, gdb works as expected. When compiled with -g,
gdb gives the following error:
(gdb) b test.d:3
Die: DW_TAG_<unknown> (abbrev = 4, offset = 77)
has children: FALSE
attributes:
DW_AT_byte_size (DW_FORM_data1) constant: 8
DW_AT_type (DW_FORM_ref4) constant ref: 69 (adjusted)
Dwarf Error: Cannot find type of die [in module /tmp/test]
Taking a look at the dwarf info for test:
% objdump --dwarf=abbrev test
-- SNIP --
4 Unknown TAG value: 41 [no children]
DW_AT_byte_size DW_FORM_data1
DW_AT_type DW_FORM_ref4
-- SNIP --
Unknown TAG value at 41... This isn't part of the dwarf spec, looking at
src/dmd/backend/dwarf2.h:
----
// D programming language extensions
DW_TAG_darray_type = 0x41,
DW_TAG_aarray_type = 0x42,
DW_TAG_delegate_type = 0x43,
DW_TAG_lo_user = 0x4080,
DW_TAG_hi_user = 0xFFFF,
----
Oh look, 0x41 is a D extension, no wonder GDB chokes :)
I'll look more into this if someone can provide me a test case which
doesn't require the D extensions to cause the error, currently this
looks like a non-bug to me as gdb doesn't support D extensions yet (yes,
this is even with a patched gdb).
Robert
