Check if /proc is usable on gdbserver start
Commit Message
Hello,
Just lost a couple of hours trying to find while gdb can't connect to gdbserver
in my debug session.
There's a buildroot where I want to debug a binary, and I tried to connect to
it from outside, but got very weird errors like architecture mismatch or
protocol errors. At last, after switching on '--debug' for gdbserver I found a
message 'Can't open /proc/pid/' message and suddenly found that I forgot to
mount procfs in my buildroot.
I think it's better to check this before running gdbserver.
Best Regards,
Slava Barinov.
Comments
On 07/04/2018 08:34 AM, Vyacheslav Barinov wrote:
> Hello,
>
> Just lost a couple of hours trying to find while gdb can't connect to gdbserver
> in my debug session.
>
> There's a buildroot where I want to debug a binary, and I tried to connect to
> it from outside, but got very weird errors like architecture mismatch or
> protocol errors. At last, after switching on '--debug' for gdbserver I found a
> message 'Can't open /proc/pid/' message and suddenly found that I forgot to
> mount procfs in my buildroot.
>
> I think it's better to check this before running gdbserver.
I'm not certain that it's a good idea to absolute require a /proc mount.
Even though we gradually moved into relying on /proc more (or better said, on
libthread_db less), over the years we've also tried to be tolerant to
missing /proc. I believe people had use cases for that (very constrained
containers or embedded systems? I don't recall exactly though...)
I assume that you're on either Aarch64 or x86_64 and that the architecture
mismatch is because gdbserver couldn't determine whether the process
was a 64-bit process, because that is done by reading the /proc/PID/exe
file. Maybe other 32-bit- or 64-bit-only archs still minimally work
without /proc.
I'm thinking that it may be prudent to downgrade this to a warning.
Would that work for you?
Thanks,
Pedro Alves
Pedro Alves <palves@redhat.com> writes:
> On 07/04/2018 08:34 AM, Vyacheslav Barinov wrote:
>> Hello,
>>
>> Just lost a couple of hours trying to find while gdb can't connect to gdbserver
>> in my debug session.
>>
>> There's a buildroot where I want to debug a binary, and I tried to connect to
>> it from outside, but got very weird errors like architecture mismatch or
>> protocol errors. At last, after switching on '--debug' for gdbserver I found a
>> message 'Can't open /proc/pid/' message and suddenly found that I forgot to
>> mount procfs in my buildroot.
>>
>> I think it's better to check this before running gdbserver.
> I'm not certain that it's a good idea to absolute require a /proc mount.
> Even though we gradually moved into relying on /proc more (or better said, on
> libthread_db less), over the years we've also tried to be tolerant to
> missing /proc. I believe people had use cases for that (very constrained
> containers or embedded systems? I don't recall exactly though...)
>
> I assume that you're on either Aarch64 or x86_64 and that the architecture
> mismatch is because gdbserver couldn't determine whether the process
> was a 64-bit process, because that is done by reading the /proc/PID/exe
> file. Maybe other 32-bit- or 64-bit-only archs still minimally work
> without /proc.
>
> I'm thinking that it may be prudent to downgrade this to a warning.
> Would that work for you?
>
> Thanks,
> Pedro Alves
You are right, I use x86_64 architecture.
Okay, if the gdbserver can work without /proc, then just warning for cases
like this is enough.
Best Regards,
Vyacheslav Barinov
From 0d9bc48e145195b9ce04dedb3ca75ee93d90a32c Mon Sep 17 00:00:00 2001
From: Slava Barinov <v.barinov@samsung.com>
Date: Wed, 4 Jul 2018 10:20:42 +0300
Subject: [PATCH] Check if /proc is usable on gdbserver start
Add check if procfs is mount and can be accessed by gdbserver.
gdbserver/
* linux-low.c (initialize_low): Add /proc check.
Signed-off-by: Slava Barinov <v.barinov@samsung.com>
---
gdb/gdbserver/linux-low.c | 7 +++++++
1 file changed, 7 insertions(+)
@@ -7553,6 +7553,13 @@ void
initialize_low (void)
{
struct sigaction sigchld_action;
+ struct stat st;
+
+ if (stat ("/proc/self", &st) != 0)
+ {
+ fprintf (stderr, "/proc is not accessible.\n");
+ exit (1);
+ }
memset (&sigchld_action, 0, sizeof (sigchld_action));
set_target_ops (&linux_target_ops);
--
2.18.0