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[patch] Support -fsplit-stack (previous frame inner to this frame)


Hi,

currently on a code with gcc -fsplit-stack `backtrace' does not work (after
the stack gets split):

(gdb) bt
#0  down (i=499) at split.c:36
#1  0x0000000000400e74 in __morestack () at ../../../gcchead/libgcc/config/i386/morestack.S:374
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

There were some intentions to remove frame_id_inner at all but then many
corrupt stacks would backtrace indefinitely.  Moreover as the current stop
PC==0 should be removed one day for corrupted backtraces unwinding (PR by me
backtrace/12237).

I had an idea to instead create non-NORMAL_FRAME by a separate sniffer like
currently present in inline-frame.c.  The problem is unwinders currently
cannot easily chain for a single frame.  And this unwinder specific for the
__morestack function needs to do standard DWARF frame unwinding.  Chaining
directly to dwarf2_frame_prev_register&co. is also not right as the code can
be compiled for example with STABS instead.

Maybe a proper unwinders chaining gets implemented one day (hacked in one for
archer-jankratochvil-entryval) but for now I find this hack acceptable myself.
Do you?

No regressions on {x86_64,x86_64-m32,i686}-fedora14-linux-gnu.  But the
testcase works for me only for GCC HEAD on Fedora 14 (+not on Fedora 13),
tested it there on x86_64 and x86_64-m32.


Thanks,
Jan


gdb/
2010-11-23  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* frame.c (morestack_start, morestack_end, frame_new_objfile): New.
	(frame_id_inner): Check l.code_addr against them.
	(_initialize_frame): Install frame_new_objfile).

gdb/testsuite/
2010-11-23  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/morestack.exp: New file.
	* gdb.base/morestack.c: New file.

--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -487,6 +487,30 @@ frame_id_eq (struct frame_id l, struct frame_id r)
   return eq;
 }
 
+/* Start and end of the `__morestack' function.  MORESTACK_END address is the
+   end plus one (exclusive) one.  */
+static CORE_ADDR morestack_start, morestack_end;
+
+/* Initialize MORESTACK_START and MORESTACK_END, provided as a cache.  */
+
+static void
+frame_new_objfile (struct objfile *objfile)
+{
+  struct minimal_symbol *msymbol;
+
+  morestack_start = morestack_end = 0;
+
+  msymbol = lookup_minimal_symbol ("__morestack", NULL, NULL);
+  if (msymbol == NULL)
+    return;
+
+  morestack_start = gdbarch_convert_from_func_ptr_addr (target_gdbarch,
+					       SYMBOL_VALUE_ADDRESS (msymbol),
+							&current_target);
+
+  morestack_end = morestack_start + MSYMBOL_SIZE (msymbol);
+}
+
 /* Safety net to check whether frame ID L should be inner to
    frame ID R, according to their stack addresses.
 
@@ -550,6 +574,12 @@ frame_id_inner (struct gdbarch *gdbarch, struct frame_id l, struct frame_id r)
 	   block with the greater depth.  */
 	inner = contained_in (lb, rb);
     }
+  else if (l.code_addr_p && morestack_start <= l.code_addr
+           && l.code_addr < morestack_end)
+    {
+      /* gcc -fsplit-stack __morestack can continue the stack anywhere.  */
+      inner = 0;
+    }
   else
     /* Only return non-zero when strictly inner than.  Note that, per
        comment in "frame.h", there is some fuzz here.  Frameless
@@ -2218,6 +2248,7 @@ _initialize_frame (void)
   obstack_init (&frame_cache_obstack);
 
   observer_attach_target_changed (frame_observer_target_changed);
+  observer_attach_new_objfile (frame_new_objfile);
 
   add_prefix_cmd ("backtrace", class_maintenance, set_backtrace_cmd, _("\
 Set backtrace specific variables.\n\
--- /dev/null
+++ b/gdb/testsuite/gdb.base/morestack.c
@@ -0,0 +1,105 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2010 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Based on the gcc testcase `gcc/testsuite/gcc.dg/split-1.c'.  This test
+   needs to use setrlimit to set the stack size, so it can only run on Unix.
+   */
+
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/resource.h>
+#include <stdio.h>
+#include <sys/mman.h>
+
+/* Use a noinline function to ensure that the buffer is not removed
+   from the stack.  */
+static void use_buffer (char *buf) __attribute__ ((noinline));
+static void
+use_buffer (char *buf)
+{
+  buf[0] = '\0';
+}
+
+static volatile int marker_var;
+
+static void
+marker_miss (void)
+{
+  marker_var = 0;
+}
+
+static void
+marker_hit (void)
+{
+  marker_var = 0;
+}
+
+void *reserved;
+#define RESERVED_SIZE 0x1000000
+
+/* Each recursive call uses 10,000 bytes.  We call it 1000 times,
+   using a total of 10,000,000 bytes.  If -fsplit-stack is not
+   working, that will overflow our stack limit.  */
+
+static void
+down (int i)
+{
+  char buf[10000];
+  static void *last;
+
+  if (last && last < (void *) buf)
+    {
+      printf ("%d: %p < %p\n", i, last, buf);
+      marker_hit ();
+    }
+  last = buf;
+
+  if (i == 500)
+    {
+      if (munmap (reserved, RESERVED_SIZE) != 0)
+        abort ();
+      reserved = NULL;
+    }
+
+  if (i > 0)
+    {
+      use_buffer (buf);
+      down (i - 1);
+    }
+  else
+    marker_miss ();
+}
+
+int
+main (void)
+{
+  struct rlimit r;
+
+  reserved = mmap (NULL, RESERVED_SIZE, PROT_READ | PROT_WRITE,
+		   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  if (reserved == MAP_FAILED)
+    abort ();
+
+  /* We set a stack limit because we are usually invoked via make, and
+     make sets the stack limit to be as large as possible.  */
+  r.rlim_cur = 8192 * 1024;
+  r.rlim_max = 8192 * 1024;
+  if (setrlimit (RLIMIT_STACK, &r) != 0)
+    abort ();
+  down (1000);
+  return 0;
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.base/morestack.exp
@@ -0,0 +1,52 @@
+# Copyright (C) 2010 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if [get_compiler_info "ignored"] {
+    return -1
+}
+
+if {$gcc_compiled == 0} {
+    return -1
+}
+
+set testfile morestack
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${testfile}.c {additional_flags=-fsplit-stack}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_breakpoint "marker_hit"
+gdb_breakpoint "marker_miss"
+
+set test "continue"
+gdb_test_multiple $test $test {
+    -re "marker_hit.*$gdb_prompt $" {
+	pass $test
+    }
+    -re "marker_miss.*$gdb_prompt $" {
+	# The testcase failed to violated the frame_id_inner condition by
+	# handing inner frame with higher (on the stack-grows-down arches)
+	# $sp address than the outer frame.
+	xfail $test
+	return 0
+    }
+}
+
+# FAIL was on `bt' producing:
+# Backtrace stopped: previous frame inner to this frame (corrupt stack?)
+gdb_test "up 3000" " in main .*"


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