From: Tom de Vries <tdevries@suse.de>
To: gdb-patches@sourceware.org
Subject: [PATCH 2/2] [gdb] Fix segfault in for_each_block, part 2
Date: Sat, 4 Nov 2023 16:57:57 +0100 [thread overview]
Message-ID: <20231104155757.16649-3-tdevries@suse.de> (raw)
In-Reply-To: <20231104155757.16649-1-tdevries@suse.de>
The previous commit describes PR gdb/30547, a segfault when running test-case
gdb.base/vfork-follow-parent.exp on powerpc64 (likewise on s390x).
The root cause for the segmentation fault is that linux_is_uclinux gives an
incorrect result: it returns true instead of false.
So, why does linux_is_uclinux:
...
int
linux_is_uclinux (void)
{
CORE_ADDR dummy;
return (target_auxv_search (AT_NULL, &dummy) > 0
&& target_auxv_search (AT_PAGESZ, &dummy) == 0);
...
return true?
This is because ppc_linux_target_wordsize returns 4 instead of 8, causing
ppc_linux_nat_target::auxv_parse to misinterpret the auxv vector.
So, why does ppc_linux_target_wordsize:
...
int
ppc_linux_target_wordsize (int tid)
{
int wordsize = 4;
/* Check for 64-bit inferior process. This is the case when the host is
64-bit, and in addition the top bit of the MSR register is set. */
long msr;
errno = 0;
msr = (long) ptrace (PTRACE_PEEKUSER, tid, PT_MSR * 8, 0);
if (errno == 0 && ppc64_64bit_inferior_p (msr))
wordsize = 8;
return wordsize;
}
...
return 4?
Specifically, we get this result because because tid == 0, so we get
errno == ESRCH.
The tid == 0 is caused by the switch_to_no_thread in
handle_vfork_child_exec_or_exit:
...
/* Switch to no-thread while running clone_program_space, so
that clone_program_space doesn't want to read the
selected frame of a dead process. */
scoped_restore_current_thread restore_thread;
switch_to_no_thread ();
inf->pspace = new program_space (maybe_new_address_space ());
...
but moving the maybe_new_address_space call to before that gives us the
same result. The tid is no longer 0, but we still get ESRCH because the
thread has exited.
Fix this in handle_vfork_child_exec_or_exit by doing the
maybe_new_address_space call in the context of the vfork parent.
Tested on top of trunk on x86_64-linux and ppc64le-linux.
Tested on top of gdb-14-branch on ppc64-linux.
PR gdb/30547
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30547
---
gdb/infrun.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 4fde96800fb..834718726a4 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1105,13 +1105,23 @@ handle_vfork_child_exec_or_exit (int exec)
go ahead and create a new one for this exiting
inferior. */
+ struct address_space *aspace;
+ {
+ /* Temporarily switch to the vfork parent, to facilitate ptrace
+ calls done during maybe_new_address_space. */
+ scoped_restore save_inferior_ptid
+ = make_scoped_restore (&inferior_ptid);
+ inferior_ptid = ptid_t (vfork_parent->pid);
+ aspace = maybe_new_address_space ();
+ }
+
/* Switch to no-thread while running clone_program_space, so
that clone_program_space doesn't want to read the
selected frame of a dead process. */
scoped_restore_current_thread restore_thread;
switch_to_no_thread ();
- inf->pspace = new program_space (maybe_new_address_space ());
+ inf->pspace = new program_space (aspace);
inf->aspace = inf->pspace->aspace;
set_current_program_space (inf->pspace);
inf->removable = true;
--
2.35.3
prev parent reply other threads:[~2023-11-04 15:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-04 15:57 [PATCH 0/2] [gdb] Fix segfault in for_each_block Tom de Vries
2023-11-04 15:57 ` [PATCH 1/2] [gdb] Fix segfault in for_each_block, part 1 Tom de Vries
2023-11-06 15:24 ` Andrew Burgess
2023-11-07 13:28 ` Tom de Vries
2023-11-06 17:05 ` Simon Marchi
2023-11-07 11:16 ` Andrew Burgess
2023-11-07 13:32 ` Tom de Vries
2023-11-04 15:57 ` Tom de Vries [this message]
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