From: Simon Marchi <simon.marchi@polymtl.ca>
To: gdb-patches@sourceware.org
Cc: Libor Bukata <libor.bukata@oracle.com>,
Simon Marchi <simon.marchi@polymtl.ca>
Subject: [PATCH 1/2] gdb: push target earlier in procfs_target::attach (PR 27435)
Date: Sun, 21 Feb 2021 10:56:29 -0500 [thread overview]
Message-ID: <20210221155630.3026942-1-simon.marchi@polymtl.ca> (raw)
Since this is a GDB 9 -> 10 regression, I would like to push it to
gdb-10-branch.
This is a follow-up to:
https://sourceware.org/pipermail/gdb-patches/2021-February/176202.html
This patch fixes a segfault seen when attaching to a process on Solaris.
The steps leading to the segfault are:
- procfs_target::attach calls do_attach, at this point the inferior's
process slot in the target stack is empty.
- do_attach adds a thread with `add_thread (&the_procfs_target, ptid)`
- in add_thread_silent, the passed target (&the_procfs_target) is
passed to find_inferior_ptid
- find_inferior_ptid returns nullptr, as there is no inferior with this
ptid that has &the_procfs_target as its process target
- the nullptr `inf` is passed to find_thread_ptid, which dereferences
it, causing a segfault
- back in procfs_target::attach, after do_attach, we push the
the_procfs_target on the inferior's target stack, although we never
reach this because the segfault happens before.
To fix this, I think we need to do the same as is done in
inf_ptrace_target::attach: push the target early and unpush it in case
the attach fails (and keep it if the attach succeeds).
Implement it by moving target_unpush_up to target.h, so it can be
re-used here. Make procfs_target::attach use it. Note that just like
is mentioned in inf_ptrace_target::attach, we should push the target
before calling target_pid_to_str, so that calling target_pid_to_str ends
up in procfs_target::pid_to_str.
Tested by trying to attach on a process on gcc211 on the gcc compile
farm.
gdb/ChangeLog:
PR gdb/27435
* inf-ptrace.c (struct target_unpusher): Move to target.h.
(target_unpush_up): Likewise.
* procfs.c (procfs_target::attach): Push target early. Use
target_unpush_up to unpush target in case of error.
* target.h (struct target_unpusher): Move here.
(target_unpush_up): Likewise.
Change-Id: I88aff8b20204e1ca1d792e27ac6bc34fc1aa0d52
---
gdb/inf-ptrace.c | 16 ----------------
gdb/procfs.c | 14 ++++++++++++--
gdb/target.h | 14 ++++++++++++++
3 files changed, 26 insertions(+), 18 deletions(-)
diff --git a/gdb/inf-ptrace.c b/gdb/inf-ptrace.c
index 0f2f56cc3660..7ca02dfd8764 100644
--- a/gdb/inf-ptrace.c
+++ b/gdb/inf-ptrace.c
@@ -49,22 +49,6 @@ gdb_ptrace (PTRACE_TYPE_ARG1 request, ptid_t ptid, PTRACE_TYPE_ARG3 addr,
#endif
}
-/* A unique_ptr helper to unpush a target. */
-
-struct target_unpusher
-{
- void operator() (struct target_ops *ops) const
- {
- unpush_target (ops);
- }
-};
-
-/* A unique_ptr that unpushes a target on destruction. */
-
-typedef std::unique_ptr<struct target_ops, target_unpusher> target_unpush_up;
-
-\f
-
inf_ptrace_target::~inf_ptrace_target ()
{}
diff --git a/gdb/procfs.c b/gdb/procfs.c
index e73faa8d41dc..cab29c3cbbcb 100644
--- a/gdb/procfs.c
+++ b/gdb/procfs.c
@@ -1767,6 +1767,14 @@ procfs_target::attach (const char *args, int from_tty)
if (pid == getpid ())
error (_("Attaching GDB to itself is not a good idea..."));
+ /* Push the target if needed, ensure it gets un-pushed it if attach fails. */
+ target_unpush_up unpusher;
+ if (!target_is_pushed (this))
+ {
+ push_target (this);
+ unpusher.reset (this);
+ }
+
if (from_tty)
{
const char *exec_file = get_exec_file (0);
@@ -1780,9 +1788,11 @@ procfs_target::attach (const char *args, int from_tty)
fflush (stdout);
}
+
do_attach (ptid_t (pid));
- if (!target_is_pushed (this))
- push_target (this);
+
+ /* Everything went fine, keep the target pushed. */
+ unpusher.release ();
}
void
diff --git a/gdb/target.h b/gdb/target.h
index 0de78075e9b5..52e23b05ffd8 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -2392,6 +2392,20 @@ extern void push_target (target_ops_up &&);
extern int unpush_target (struct target_ops *);
+/* A unique_ptr helper to unpush a target. */
+
+struct target_unpusher
+{
+ void operator() (struct target_ops *ops) const
+ {
+ unpush_target (ops);
+ }
+};
+
+/* A unique_ptr that unpushes a target on destruction. */
+
+typedef std::unique_ptr<struct target_ops, target_unpusher> target_unpush_up;
+
extern void target_pre_inferior (int);
extern void target_preopen (int);
--
2.30.1
next reply other threads:[~2021-02-21 15:56 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-21 15:56 Simon Marchi [this message]
2021-02-21 15:56 ` [PATCH 2/2] gdb: add asserts in thread code Simon Marchi
2021-02-21 21:04 ` [PATCH 1/2] gdb: push target earlier in procfs_target::attach (PR 27435) Tom Tromey
2021-02-21 21:18 ` Simon Marchi
2021-02-22 11:03 ` Libor Bukata
2021-02-22 16:51 ` Simon Marchi
2021-02-23 6:35 ` Libor Bukata
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