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Re: [PATCH] Temporarily revert Steven's PCH changes for 4.8 (PR pch/54117)

On Wed, Feb 13, 2013 at 4:54 PM, Jakub Jelinek wrote:
> Hi!
> As agreed on in the PR, here is the revertion of 3 commits, so that
> PCH works again for -gstabs and other debug info formats for 4.8
> release.  For 4.9 we should either remove support for anything non-DWARF, or
> hope somebody steps up and fixes dbxout.c etc. not to emit debug info right
> away, but queue it till end of compilation.


I'd still like to propose deprecating all stabs support for GCC 4.8 and
remove it for GCC 4.9 (i.e. dbxout, sdbout, xcoffout).

It's not a very useful debug info format, after all.  The only
argument against DWARF, that it is so much larger than stabs,
is something I haven't been able to reproduce (see and
DWARF compression via dwz, and debug-fission will improve things
even further.

An important question is of course: Who still *needs* stabs? If there
are important platforms that need stabs support to continue to work,
then deprecating is probably not a realistic option yet...

The list of platforms that are IMHO blockers rights now, with possible
solutions for GCC 4.9, are:

* hppa2.0w-hp-hpux11.11 - no solution immediately available
* powerpc-ibm-aix* - only support AIX7 and later
   -> deprecate AIX6 and older in GCC 4.8
* ix86-*-openbsd2.*, ix86-*openbsd3.[0123] - OpenBSD 3.3 was released
  in May 2003 -> deprecate for GCC 4.8
* m68k*-*-openbsd - port has seen no active maintenance, and has no
  test results posted, ever -> deprecate for GCC 4.8
* pdp11-*-* - toy port -> default to DEBUG_NONE
* ix86-*-interix* - no solution immediately available, and no-one
  listed in MAINTAINERS to ask for help, so maybe Doug can say
  something about this one?

Platforms that support DWARF2+ but currently have another default
preferred debug info type, would be changed to default to DWARF2+.

So older AIX and 32-bits HPUX are the only real problem cases.


All GCC 4.8 primary platforms support DWARF2+, and AFAICT they all have
it as their PREFERRED_DEBUGGING_TYPE (including freebsd):

* arm-linux-gnueabi
* i386-unknown-freebsd
* i686-pc-linux-gnu
* mipsisa64-elf
* powerpc64-unknown-linux-gnu
* sparc-sun-solaris2.10
* x86_64-unknown-linux-gnu

Most of the above also include other debug info types by default, but
DWARF2+ is the default.

For the secondary platforms list things are not so simple. Some of them
have a non-DWARF PREFERRED_DEBUGGING_TYPE by default, and some only
conditionally (old configurations):

* hppa2.0w-hp-hpux11.11 -> DBX_DEBUGGING_INFO
    For 32-bits only, but that's the most common subtarget.
    According to Dave, it should be possible to add DRAWF2+ support:
    Perhaps Dave can explain what would have to be done to move this
    platform to DWARF2...?

* powerpc-ibm-aix7.1.0.0 -> XCOFF_DEBUGGING_INFO
    I think this is for historical reasons. AIX7 has DWARF support,
    but it looks like that's not yet implemented in GCC.
    Older AIX do not support DWARF, AFAICT (David E.?).

* i686-apple-darwin -> DBX_DEBUGGING_INFO
    MacOSX10.4, 32-bits (darwin8).
    All 64bits and darwin9+ prefer DWARF2.

* i686-pc-cygwin, i686-mingw32 -> DBX_DEBUGGING_INFO
    With binutils 2.16 and later, DWARF2_DEBUGGING_INFO is the default:

* s390x-linux-gnu -> DWARF2_DEBUGGING_INFO

Other platforms that support DWARF2+ and have it as the preferred type:
* *-*-elf* via:
  This is practically all ELF platforms.  A few target headers redefine
  Exceptions are microblaze*-*-rtems*, microblaze*-*-elf*
* tic6x-*-*, ix86-*-nto-qnx* via:
  config/tm-dwarf2.h:#define  PREFERRED_DEBUGGING_TYPE  DWARF2_DEBUG
* *-*-vxworks* via:
  config/vx-common.h:#define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
* alpha*-dec-*vms* via:
* hppa*64*-*-hpux11* via:
  config/pa/pa64-hpux.h:#define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG

Other platforms that support DWARF2+ but prefer another debug info type
by default:
* rx-*-elf* if using TARGET_AS100_SYNTAX, via:
  config/rx/rx.h:#define PREFERRED_DEBUGGING_TYPE (TARGET_AS100_SYNTAX \
  config/rx/rx.h:                            ? DBX_DEBUG : DWARF2_DEBUG)
* avr-*-* includes elfos.h but changes preffered debug info type via:
  config/avr/elf.h:#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
* powerpc-*-lynxos*, ix86-*-lynxos* include elfos.h but change the
  preffered debug info type via:
* ix86-pc-msdosdjgpp*, supports DWARF2+ via:
  config/i386/djgpp.h:#define DWARF2_DEBUGGING_INFO 1
  but picks up its preferred debug info via:
  config/dbxcoff.h:#define PREFERRED_DEBUGGING_TYPE SDB_DEBUG
* mn10300-*-*, v850*-*-* if configured --with-stabs, via

Targets that do not support DWARF2+:
* ix86-*-openbsd2.*, ix86-*openbsd3.[0123]
* m68k*-*-openbsd via config/m68k/openbsd.h:#define DBX_DEBUGGING_INFO 1
  and no other files included that define another debug info type.
* pdp11-*-*: config/pdp11/pdp11.h:#define DBX_DEBUGGING_INFO
* ix86-*-interix* via:
  config/i386/i386-interix.h:#define DBX_DEBUGGING_INFO 1
  config/i386/i386-interix.h:#define SDB_DEBUGGING_INFO 1
  config/i386/i386-interix.h:#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
  and picks up nothing else from other header files.

Unknown platforms:
* config/arm/coff.h:#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
  Does any platform use this file?

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