http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53453
Bug #: 53453
Summary: darwin linker expects both AT_name and AT_comp_dir
debug notes
Classification: Unclassified
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: howa...@nitro.med.uc.edu
Future versions of dsymutil on darwin will emit warnings of the form...
warning: no debug symbols in executable (-arch x86_64)
warning: no debug symbols in executable (-arch i386)
when the debug note for AT_comp_dir is missing from linked object files.
Upstream had the following comments...
------------------------------------------------------------------------
The issue is not directly dsymutil. The way it works on darwin, is that
the linker does not copy dwarf debug info. Instead, the linker leaves
the debug info in the .o files and then puts "debug notes" into the final
linked image. If you run the program under gdb, the debugger sees the
notes and opens the .of files and reads the dwarf. If instead you run
dysmtuil, it reads the debug notes which tells it where to find the
.o files from which to read the dwarf and merge all the dwarf into
the .dSYM.
The dsymtuil warning is that no dwarf was found. In this case that
is because there were no debug notes recorded by the linker which
was because of the lack of AT_comp_dir. In some of the cases you've
set up, there was no warning because there was some dwarf found but
not all dwarf was found, so the .dSYM is less than ideal.
The format of the debug notes requires a pair of dir/file. Because
it always just worked before, the linker just copied the dir from
AT_comp_dir and the file from AT_name. It does not look like the
dwarf spec requires the AT_comp_dir, but it has always been there
before and the linker has come to depend on it.
-------------------------------------------------------------------------
This issue can be demonstrated with Xcode 4.2 under 10.7.4 using gcc trunk...
howarth% gcc-fsf-4.8
/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20120520/gcc/testsuite/gcc.c-torture/execute/builtins/20010124-1.c
/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20120520/gcc/testsuite/gcc.c-torture/execute/builtins/20010124-1-lib.c
/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20120520/gcc/testsuite/gcc.c-torture/execute/builtins/lib/main.c
-fno-diagnostics-show-caret --save-temps -w -O3 -g -lm -m64 -o 20010124-1.x4
howarth% dwarfdump --debug-info main.o | grep -A3 AT_language
AT_language( DW_LANG_C89 )
AT_name(
"/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20120520/gcc/testsuite/gcc.c-torture/execute/builtins/lib/main.c"
)
AT_stmt_list( 0x00000000 )
whereas if you copy or symlink the source files into a local directory and
compile with...
howarth% gcc-fsf-4.8 20010124-1.c 20010124-1-lib.c main.c
-fno-diagnostics-show-caret --save-temps -w -O3 -g -lm -m64 -o 20010124-1.x4
...both the AT_name and AT_comp_dir debug notes are present...
howarth% dwarfdump --debug-info main.o | grep -A3 AT_language
AT_language( DW_LANG_C89 )
AT_name( "main.c" )
AT_comp_dir( "/Users/howarth/xcode44_bugv2/good_binary" )
AT_stmt_list( 0x00000000 )
and future dsymutil releases won't emit the warning.
