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f9582a22db
When running test-case gdb.base/vfork-follow-parent.exp on powerpc64 (likewise
on s390x), I run into:
...
(gdb) PASS: gdb.base/vfork-follow-parent.exp: \
exec_file=vfork-follow-parent-exit: target-non-stop=on: non-stop=off: \
resolution_method=schedule-multiple: print unblock_parent = 1
continue^M
Continuing.^M
Reading symbols from vfork-follow-parent-exit...^M
^M
^M
Fatal signal: Segmentation fault^M
----- Backtrace -----^M
0x1027d3e7 gdb_internal_backtrace_1^M
src/gdb/bt-utils.c:122^M
0x1027d54f _Z22gdb_internal_backtracev^M
src/gdb/bt-utils.c:168^M
0x1057643f handle_fatal_signal^M
src/gdb/event-top.c:889^M
0x10576677 handle_sigsegv^M
src/gdb/event-top.c:962^M
0x3fffa7610477 ???^M
0x103f2144 for_each_block^M
src/gdb/dcache.c:199^M
0x103f235b _Z17dcache_invalidateP13dcache_struct^M
src/gdb/dcache.c:251^M
0x10bde8c7 _Z24target_dcache_invalidatev^M
src/gdb/target-dcache.c:50^M
...
or similar.
The root cause for the segmentation fault is that linux_is_uclinux gives an
incorrect result: it should always return false, given that we're running on a
regular linux system, but instead it returns first true, then false.
In more detail, the segmentation fault happens as follows:
- a program space with an address space is created
- a second program space is about to be created. maybe_new_address_space
is called, and because linux_is_uclinux returns true, maybe_new_address_space
returns false, and no new address space is created
- a second program space with the same address space is created
- a program space is deleted. Because linux_is_uclinux now returns false,
gdbarch_has_shared_address_space (current_inferior ()->arch ()) returns
false, and the address space is deleted
- when gdb uses the address space of the remaining program space, we run into
the segfault, because the address space is deleted.
Hardcoding linux_is_uclinux to false makes the test-case pass.
We leave addressing the root cause for the following commit in this series.
For now, prevent the segmentation fault by making the address space a refcounted
object.
This was already suggested here [1]:
...
A better solution might be to have the address spaces be reference counted
...
Tested on top of trunk on x86_64-linux and ppc64le-linux.
Tested on top of gdb-14-branch on ppc64-linux.
Co-Authored-By: Simon Marchi <simon.marchi@polymtl.ca>
PR gdb/30547
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30547
[1] https://sourceware.org/pipermail/gdb-patches/2023-October/202928.html
88 lines
2.1 KiB
C++
88 lines
2.1 KiB
C++
/* Base class of intrusively reference-counted objects.
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Copyright (C) 2017-2023 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef COMMON_REFCOUNTED_OBJECT_H
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#define COMMON_REFCOUNTED_OBJECT_H
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/* Base class of intrusively reference-countable objects.
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Incrementing and decrementing the reference count is an external
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responsibility. */
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class refcounted_object
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{
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public:
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refcounted_object () = default;
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/* Increase the refcount. */
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void incref ()
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{
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gdb_assert (m_refcount >= 0);
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m_refcount++;
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}
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/* Decrease the refcount. */
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void decref ()
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{
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m_refcount--;
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gdb_assert (m_refcount >= 0);
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}
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int refcount () const { return m_refcount; }
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private:
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DISABLE_COPY_AND_ASSIGN (refcounted_object);
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/* The reference count. */
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int m_refcount = 0;
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};
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/* A policy class to interface gdb::ref_ptr with a
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refcounted_object. */
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struct refcounted_object_ref_policy
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{
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static void incref (refcounted_object *ptr)
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{
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ptr->incref ();
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}
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static void decref (refcounted_object *ptr)
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{
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ptr->decref ();
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}
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};
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/* A policy class to interface gdb::ref_ptr with a refcounted_object, that
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deletes the object once the refcount reaches 0.. */
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template<typename T>
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struct refcounted_object_delete_ref_policy
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{
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static void incref (T *obj)
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{ obj->incref (); }
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static void decref (T *obj)
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{
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obj->decref ();
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if (obj->refcount () == 0)
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delete obj;
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}
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};
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#endif /* COMMON_REFCOUNTED_OBJECT_H */
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