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Re: [PATCH] Add UNSUPPORTED check in elf/tst-pldd.
- From: Stefan Liebler <stli at linux dot ibm dot com>
- To: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>, Florian Weimer <fweimer at redhat dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Tue, 3 Sep 2019 08:30:29 +0200
- Subject: Re: [PATCH] Add UNSUPPORTED check in elf/tst-pldd.
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On 9/2/19 9:37 PM, Adhemerval Zanella wrote:
As there are systems where ptrace_scope is configured to 1 by default,
we should adjust the testcase as the FAIL is misleading.
(I've just recognized that Steve Ellcey had also seen this FAIL:
On 29/08/2019 05:47, Florian Weimer wrote:
* Stefan Liebler:
On 8/28/19 11:24 AM, Florian Weimer wrote:
* Stefan Liebler:
target_process (void *arg)
+ if (ptrace_scope == 1)
+ /* YAMA is configured to "restricted ptrace".
+ Disable the restriction for this subprocess. */
+ support_ptrace_process_set_ptracer_any ();
I think this has a race condition if pldd attaches to the process before
the support_ptrace_process_set_ptracer_any call. I have no idea how
hard it is in practice to hit this race. It should be possible to use a
process-shared barrier or some other form of synchronization to avoid
I've added a synchronization with stdatomic.h on a shared memory mapping.
I've not used pthread* functions as I don't want to link against
libpthread.so. Then further adjustments are needed.
Or should I just restrict the test ptrace_scope 0 as Adhemerval has
proposed in his post?
Is it possible to create a process tree like this?
parent (performs output checks)
subprocess 1 (becomes pldd via execve)
If you execve pldd from subprocess 1, wouldn't subprocess 2 in its
ptrace scope for ptrace_scope < 2?
Do we really need that ad-hoc support on tst-pldd to make it support
I don't oppose the support Stefan has added on latest iteration to
make it work, but this is a lot of code to support a very specific
The minimum change should be to detect ptrace_scope == 1 and mark the
test as UNSUPPORTED. Or we change a bit more and let the test also run
in this scenario. (Either by support_ptrace_process_set_ptracer_any or
adjusting the subprocess-tree)