"Joseph S. Myers" <jos...@codesourcery.com> writes:
> On Tue, 30 Apr 2013, Rainer Orth wrote:
>
>> * gcc.c (LINK_COMPRESS_DEBUG_SPEC, ASM_COMPRESS_DEBUG_SPEC):
>> Define.
>> (LINK_COMMAND_SPEC): Invoke LINK_COMPRESS_DEBUG_SPEC.
>> (asm_options): Invoke ASM_COMPRESS_DEBUG_SPEC.
>
> Note that there are separate copies of LINK_COMMAND_SPEC in darwin.h and
> i386/djgpp.h, which maybe should include the new spec.
I hadn't thought about that. Here's what I found:
* Darwin is Mach-O, but current gas supports DWARF-in-Mach-O.
Unfortunately, current gcc mainline only supports Apple as:
i386/darwin.h hardcodes as-only options in ASM_SPEC, which causes gas
to barf. If you manually invoke gas on gcc -gdwarf output, you get
compressed debug sections, though objdump cannot handle them.
* DJGPP is COFF, but again gas seems to support DWARF. Unfortunately,
current gcc mainline doesn't even build:
gcc/config/i386/i386.c: In function 'void ix86_code_end()':
gcc/config/i386/i386.c:8667: error: 'ASM_DECLARE_FUNCTION_NAME' was not
declared in this scope
I didn't look further from here.
Anyway, I tried a i386-pc-solaris2.11 x i686-pc-darwin build with the
following patch to check it doesn't break the build:
* config/darwin.h (LINK_COMMAND_SPEC_A): Invoke
LINK_COMPRESS_DEBUG_SPEC.
* config/i386/djgpp.h (LINK_COMMAND_SPEC): Likewise.
diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -171,7 +171,8 @@ extern GTY(()) int darwin_ms_struct;
LINK_PLUGIN_SPEC \
"%{flto*:%<fcompare-debug*} \
%{flto*} \
- %l %X %{s} %{t} %{Z} %{u*} \
+ %l " LINK_COMPRESS_DEBUG_SPEC \
+ "%X %{s} %{t} %{Z} %{u*} \
%{e*} %{r} \
%{o*}%{!o:-o a.out} \
%{!nostdlib:%{!nostartfiles:%S}} \
diff --git a/gcc/config/i386/djgpp.h b/gcc/config/i386/djgpp.h
--- a/gcc/config/i386/djgpp.h
+++ b/gcc/config/i386/djgpp.h
@@ -80,7 +80,8 @@ along with GCC; see the file COPYING3.
#undef LINK_COMMAND_SPEC
#define LINK_COMMAND_SPEC \
"%{!fsyntax-only: \
-%{!c:%{!M:%{!MM:%{!E:%{!S:%(linker) %l %X %{o*} %{e*} %{N} %{n} \
+%{!c:%{!M:%{!MM:%{!E:%{!S:%(linker) %l " LINK_COMPRESS_DEBUG_SPEC \
+"%X %{o*} %{e*} %{N} %{n} \
\t%{r} %{s} %{t} %{u*} %{z} %{Z}\
\t%{!nostdlib:%{!nostartfiles:%S}}\
\t%{static:} %{L*} %D %o\
Especially darwin.h LINK_COMMAND_SPEC_A is a total mess: it's a copy of
gcc.c LINK_COMMAND_SPEC with various changes not carried forward and
other parts done in a slightly different syntax for no apparent reason.
I'm pretty sure the two could be merged to avoid problems from
duplication in the future, but I'll leave that to the Darwin
maintainers.
I can include the snippet above for symmetry, if only to reject -gz as
on ELF targets without the toolchain support, if you prefer.
> It's not clear to me from the documentation added by this patch whether
> users are meant to specify their -gz options when compiling, when linking,
> or both - and whether there might be cases when such an option is accepted
> for one of compiling and linking but not the other (which would be
> especially confusing).
The goal is to have -gz work for both compilation and linking, but
unfortunately, the current situation very much depends on both the
toolchain used and your intentions. The following matrix shows read and
write support in the GNU and Solaris toolchains. For the latter, full
support for zlib and zlib-gnu formats is being worked on, with ld
already there.
GNU Solaris
gas gld gold gdb as ld dbx
w r w r w r w r w r
none x x x x x x x x x x
zlib-gnu x x x x x x x
zlib x x
I plan to add zlib support first to gas and gdb, eventually to gld
(which also means adding support for compression on output, though I had
a very hard time finding my way through bfd and gld in the past), but
will rely on Cary Coutant and/or Ian, who were involved in the zlib/ELF
gABI format design, to handle gold.
Right now, the gas/gold combination supports -gz just fine (producing
the zlib-gnu format), while gas/gld only support -gz in the assemble
step. I know this is highly undesirable, but whether or not it's
acceptable depends on your goals:
* If you mean to trade compilation/assembly speed for disk usage, -gz
for compilation only is ok.
* If your primary goal is space savings for executables and shared
objects while still allowing debugability, you need to use gold for
-gz at link time to work.
Rainer
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Rainer Orth, Center for Biotechnology, Bielefeld University
