On 04/04/2015 09:40, Corinna Vinschen wrote:
On Apr 3 23:09, Jon TURNEY wrote:
On 01/04/2015 15:22, Corinna Vinschen wrote:
On Apr 1 14:19, Jon TURNEY wrote:
Add ucontext.h header, defining ucontext_t and mcontext_t types.
Provide sigaction sighandlers with a ucontext_t parameter, containing stack and
context information.
* include/sys/ucontext.h : New header.
* include/ucontext.h : Ditto.
* exceptions.cc (call_signal_handler): Provide ucontext_t
parameter to signal handler function.
Patch is ok with a single change: Please add a "FIXME?" comment to:
else
RtlCaptureContext();
On second thought, calling RtlCaptureContext here is probably wrong.
Wrong and also dangerous.
This causes random crashes on x86.
It seems that RtlCaptureContext requires the framepointer of the calling
function in ebp, which it uses to report the rip and rsp of it's caller.
It also seems that gcc can decide to optimize the setting of the
framepointer away, irrespective of the fact that -fomit-frame-pointer is not
used when building exceptions.cc
If _cygtls::call_signal_handler() happens to get called with ebp pointing to
an invalid memory address, as seems to happen occasionally, we will fault in
RtlCaptureContext. (in all cases, the eip and ebp in the returned context
are incorrect)
I wrote the attached patch, which fakes a callframe for RtlCaptureContext to
avoid these possible crashes, but this needs more work to correctly report
eip and ebp
Maybe it's simpler than that? Looking into the GCC info pages, I found
this:
Starting with GCC version 4.6, the default setting (when not
optimizing for size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86
targets has been changed to '-fomit-frame-pointer'. The default
can be reverted to '-fno-omit-frame-pointer' by configuring GCC
with the '--enable-frame-pointer' configure option.
Enabled at levels '-O', '-O2', '-O3', '-Os'.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Very good. I hadn't noticed that sentence and was just looking at the
"-O also turns on -fomit-frame-pointer on machines where doing so does
not interfere with debugging. "
So it seems adding -fomit-frame-pointer file by file in Makefile.in
(when building with -O2) is moot and only has an effect when building
unoptimized, otherwise all files are built with -fomit-frame-pointer
anyway.
So, what if we drop all the -fomit-frame-pointer from Makefile.in and
add an
exceptions_CFLAGS:=-fno-omit-frame-pointer
Does that help?
Yes, that seems to do the trick. Patch attached.
From cd8532832c92d10c1a3c1fb9ec705df0ea003e28 Mon Sep 17 00:00:00 2001
From: Jon TURNEY <[email protected]>
Date: Sat, 4 Apr 2015 16:18:56 +0100
Subject: [PATCH] Compile exceptions.cc with -fno-omit-frame-pointer on x86
Selectively using -fomit-frame-pointer when -O is used doesn't make sense
anymore, apparently since gcc 4.6, -O implies -fomit-frame-pointer.
exceptions.cc must be compiled with -fno-omit-frame-pointer on x86, as it uses
RtlCaptureContext, which requires a frame pointer.
* Makefile.in : Remove setting -fomit-frame-pointer for compiling
various files, it is already the default. Set
-fno-omit-frame-pointer for exceptions.cc on x86.
Signed-off-by: Jon TURNEY <[email protected]>
---
winsup/cygwin/ChangeLog | 6 +++++
winsup/cygwin/Makefile.in | 57 ++++-------------------------------------------
2 files changed, 10 insertions(+), 53 deletions(-)
diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 5ada35d..a8f4e00 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,9 @@
+2015-04-04 Jon TURNEY <[email protected]>
+
+ * Makefile.in : Remove setting -fomit-frame-pointer for compiling
+ various files, it is already the default. Set
+ -fno-omit-frame-pointer for exceptions.cc on x86.
+
2015-04-03 Takashi Yano <[email protected]>
* fhandler_tty.cc (fhandler_pty_slave::read): Change calculation of
diff --git a/winsup/cygwin/Makefile.in b/winsup/cygwin/Makefile.in
index 9b82f0a..af9faf6 100644
--- a/winsup/cygwin/Makefile.in
+++ b/winsup/cygwin/Makefile.in
@@ -449,59 +449,10 @@ INSTOBJS:=automode.o binmode.o textmode.o textreadmode.o
TARGET_LIBS:=$(LIB_NAME) $(CYGWIN_START) $(GMON_START) $(LIBGMON_A) $(SUBLIBS)
$(INSTOBJS) $(EXTRALIBS)
ifneq "${filter -O%,$(CFLAGS)}" ""
-cygheap_CFLAGS:=-fomit-frame-pointer
-cygthread_CFLAGS:=-fomit-frame-pointer
-cygtls_CFLAGS:=-fomit-frame-pointer
-cygwait_CFLAGS=-fomit-frame-pointer
-delqueue_CFLAGS:=-fomit-frame-pointer
-devices_CFLAGS:=-fomit-frame-pointer
-dir_CFLAGS:=-fomit-frame-pointer
-dlfcn_CFLAGS:=-fomit-frame-pointer
-dll_init_CFLAGS:=-fomit-frame-pointer
-dtable_CFLAGS:=-fomit-frame-pointer -fcheck-new
-fcntl_CFLAGS:=-fomit-frame-pointer
-fenv_CFLAGS:=-fomit-frame-pointer
-fhandler_CFLAGS:=-fomit-frame-pointer
-fhandler_clipboard_CFLAGS:=-fomit-frame-pointer
-fhandler_console_CFLAGS:=-fomit-frame-pointer
-fhandler_disk_file_CFLAGS:=-fomit-frame-pointer
-fhandler_dsp_CFLAGS:=-fomit-frame-pointer
-fhandler_floppy_CFLAGS:=-fomit-frame-pointer
-fhandler_netdrive_CFLAGS:=-fomit-frame-pointer
-fhandler_proc_CFLAGS:=-fomit-frame-pointer
-fhandler_process_CFLAGS:=-fomit-frame-pointer
-fhandler_random_CFLAGS:=-fomit-frame-pointer
-fhandler_raw_CFLAGS:=-fomit-frame-pointer
-fhandler_registry_CFLAGS:=-fomit-frame-pointer
-fhandler_serial_CFLAGS:=-fomit-frame-pointer
-fhandler_socket_CFLAGS:=-fomit-frame-pointer
-fhandler_syslog_CFLAGS:=-fomit-frame-pointer
-fhandler_tape_CFLAGS:=-fomit-frame-pointer
-fhandler_termios_CFLAGS:=-fomit-frame-pointer
-fhandler_tty_CFLAGS:=-fomit-frame-pointer
-fhandler_virtual_CFLAGS:=-fomit-frame-pointer
-fhandler_windows_CFLAGS:=-fomit-frame-pointer
-fhandler_zero_CFLAGS:=-fomit-frame-pointer
-flock_CFLAGS:=-fomit-frame-pointer
-grp_CFLAGS:=-fomit-frame-pointer
-libstdcxx_wrapper_CFLAGS:=-fomit-frame-pointer
-localtime_CFLAGS:=-fwrapv
-malloc_CFLAGS:=-fomit-frame-pointer -O3
-malloc_wrapper_CFLAGS:=-fomit-frame-pointer
-miscfuncs_CFLAGS:=-fomit-frame-pointer
-net_CFLAGS:=-fomit-frame-pointer
-passwd_CFLAGS:=-fomit-frame-pointer
-path_CFLAGS=-fomit-frame-pointer
-regcomp_CFLAGS=-fomit-frame-pointer
-regerror_CFLAGS=-fomit-frame-pointer
-regexec_CFLAGS=-fomit-frame-pointer
-regfree_CFLAGS=-fomit-frame-pointer
-shared_CFLAGS:=-fomit-frame-pointer
-sync_CFLAGS:=-fomit-frame-pointer -O3
-smallprint_CFLAGS:=-fomit-frame-pointer
-syscalls_CFLAGS:=-fomit-frame-pointer
-sysconf_CFLAGS:=-fomit-frame-pointer
-uinfo_CFLAGS:=-fomit-frame-pointer
+ifeq ($(target_cpu),i686)
+# on x86, exceptions.cc must be compiled with a frame-pointer as it uses
RtlCaptureContext()
+exceptions_CFLAGS:=-fno-omit-frame-pointer
+endif
endif
fhandler_proc_CFLAGS+=-DUSERNAME="\"$(USER)\"" -DHOSTNAME="\"$(HOSTNAME)\""
--
2.1.4
