[COMMITTED] Use pragmas rather than makefiles for necessary options for unwind code.
Commit Message
Verified on x86_64-linux-gnu that no generated code (including unwind info)
changes. Also tested arm-linux-gnueabihf that no generated code changes;
there was one difference in the EABI unwind info for __unwind_freeres,
which I don't understand but also deem wholly unimportant.
Thanks,
Roland
2014-12-16 Roland McGrath <roland@hack.frob.com>
* nptl/unwind.c: Use pragma to turn on -fexceptions.
* sysdeps/nptl/unwind-forcedunwind.c: Use pragma to turn on
-fexceptions and -fasynchronous-unwind-tables.
* sysdeps/unix/sysv/linux/arm/unwind-forcedunwind.c: Likewise.
* sysdeps/gnu/unwind-resume.c: Likewise.
* nptl/Makefile (CFLAGS-unwind.c, CFLAGS-unwind-forcedunwind.c):
Variables removed.
* sysdeps/gnu/Makefile
[$(subdir) = csu] (CFLAGS-unwind-resume.c): Likewise.
[$(subdir) = rt] (CFLAGS-rt-unwind-resume.c): Likewise.
Comments
On Tue, 16 Dec 2014, Roland McGrath wrote:
> Verified on x86_64-linux-gnu that no generated code (including unwind info)
> changes. Also tested arm-linux-gnueabihf that no generated code changes;
> there was one difference in the EABI unwind info for __unwind_freeres,
> which I don't understand but also deem wholly unimportant.
I don't think this is safe. The optimize pragma is documented as being
for optimization options only; using it with other options such as
-fexceptions is not a documented or supported GCC feature (actually, even
using it for some optimization options can be very fragile; it's best to
use it only for purely non-semantic options rather than those such as
-ffast-math that affect semantics). -fexceptions affects global state in
GCC, including global choices made when the parser is initialized [*];
enabling it at any later point risks subtle problems from inconsistencies
in GCC's internal datastructures; that it works with a particular version
of GCC at a particular time means very little. Enabling it after headers
(probably including inline functions) have been parsed seems even riskier
than enabling it at the start of a source file before any headers have
been parsed (but I still don't think that would be safe).
[*] using_eh_for_cleanups - on that basis, it seems quite plausible that
cleanup attributes (as used in various ways in glibc) will not reliably
interact properly with exceptions if exceptions weren't enabled from the
command line.
OK. I've reverted it (including the ChangeLog and all, since there were no
later commits anyway).
I was eager to do this because I thought it was going to simplify some
other changes I'm working on. But I changed tack on that work anyway
so I think this is now wholly orthogonal.
Thanks,
Roland
@@ -146,9 +146,6 @@ libpthread-static-only-routines = pthread_atfork
# nptl-init.c contains sigcancel_handler().
CFLAGS-nptl-init.c = -fexceptions -fasynchronous-unwind-tables
-# The unwind code itself,
-CFLAGS-unwind.c = -fexceptions
-CFLAGS-unwind-forcedunwind.c = -fexceptions -fasynchronous-unwind-tables
# The following three functions must be async-cancel safe.
CFLAGS-pthread_cancel.c = -fexceptions -fasynchronous-unwind-tables
@@ -25,6 +25,8 @@
#include "pthreadP.h"
#include <jmpbuf-unwind.h>
+#pragma GCC optimize "-fexceptions"
+
#ifdef HAVE_FORCED_UNWIND
#ifdef _STACK_GROWS_DOWN
@@ -79,11 +79,9 @@ endif
ifeq ($(subdir),csu)
routines += unwind-resume
shared-only-routines += unwind-resume
-CFLAGS-unwind-resume.c += -fexceptions -fasynchronous-unwind-tables
endif
ifeq ($(subdir),rt)
librt-sysdep_routines += rt-unwind-resume
librt-shared-only-routines += rt-unwind-resume
-CFLAGS-rt-unwind-resume.c += -fexceptions -fasynchronous-unwind-tables
endif
@@ -21,6 +21,8 @@
#include <unwind.h>
#include <gnu/lib-names.h>
+#pragma GCC optimize ("-fexceptions", "-fasynchronous-unwind-tables")
+
static void (*libgcc_s_resume) (struct _Unwind_Exception *exc)
__attribute__ ((noreturn));
static _Unwind_Reason_Code (*libgcc_s_personality)
@@ -23,6 +23,8 @@
#include <sysdep.h>
#include <gnu/lib-names.h>
+#pragma GCC optimize ("-fexceptions", "-fasynchronous-unwind-tables")
+
static void *libgcc_s_handle;
static void (*libgcc_s_resume) (struct _Unwind_Exception *exc);
static _Unwind_Reason_Code (*libgcc_s_personality)
@@ -21,6 +21,8 @@
#include <unwind.h>
#include <pthreadP.h>
+#pragma GCC optimize ("-fexceptions", "-fasynchronous-unwind-tables")
+
static void *libgcc_s_handle;
static void (*libgcc_s_resume) (struct _Unwind_Exception *exc)
__attribute_used__;