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Bug 2034494 - gcc: Use _thread_db_sizeof_pthread in ThreadDescriptorSize
Summary: gcc: Use _thread_db_sizeof_pthread in ThreadDescriptorSize
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 9
Classification: Red Hat
Component: gcc
Version: 9.0
Hardware: All
OS: Linux
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Marek Polacek
QA Contact: Václav Kadlčík
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2021-12-21 06:43 UTC by Florian Weimer
Modified: 2023-07-18 14:25 UTC (History)
4 users (show)

Fixed In Version: gcc-11.2.1-9.3.el9
Doc Type: No Doc Update
Doc Text:
Clone Of:
: 2034497 (view as bug list)
Environment:
Last Closed: 2022-05-17 15:55:42 UTC
Type: Bug
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Github llvm llvm-project issues 52989 0 None open [libsanitizer] Use _thread_db_sizeof_pthread in ThreadDescriptorSize 2022-01-04 16:13:04 UTC
Red Hat Issue Tracker RHELPLAN-106306 0 None None None 2021-12-21 06:50:44 UTC
Red Hat Product Errata RHBA-2022:3966 0 None None None 2022-05-17 15:56:11 UTC

Description Florian Weimer 2021-12-21 06:43:46 UTC 
GCC currently hard-codes the size of struct pthread in the sanitizers, in ThreadDescriptorSize in libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cpp.

Starting with glibc 2.34 and this commit

commit fef400a2f976d1fd6a4639e6980f6c50ee13fbf5
Author: Florian Weimer <fweimer>
Date:   Mon Jun 28 14:33:53 2021 +0200

    nptl: Export libthread_db-used symbols under GLIBC_PRIVATE
    
    This allows distributions to strip debugging information from
    libc.so.6 without impacting the debugging experience.
    
    Reviewed-by: Carlos O'Donell <carlos>

it is possible to determine sizeof (struct pthread) using dl(v)sym, like this:

  const unsigned int *psize = dlvsym(RTLD_DEFAULT, "_thread_db_sizeof_pthread",
                                     "GLIBC_PRIVATE");
  if (psize != nullptr) {
    val = *psize;
    atomic_store_relaxed(&thread_descriptor_size, val);
    return val;
  }

I'm not sure if upstream (GCC or Clang) will take this change, but we should definitely make it downstream, to avoid mysterious sanitizer problems if we need to change struct pthread in glibc.
Comment 1 Marek Polacek 2022-01-03 21:19:05 UTC 
That change would be fine with me but I think we should at least have an upstream bug report.
Comment 2 Marek Polacek 2022-01-04 15:53:44 UTC 
(In reply to Marek Polacek from comment #1)
> That change would be fine with me but I think we should at least have an
> upstream bug report.

Opened: https://github.com/llvm/llvm-project/issues/52989
Comment 3 Marek Polacek 2022-01-31 16:39:33 UTC 
I'll leave this for RHEL 9.1, I think.
Comment 5 Florian Weimer 2022-01-31 16:57:19 UTC 
(In reply to Marek Polacek from comment #3)
> I'll leave this for RHEL 9.1, I think.

I changed the layout of struct pthread in glibc-2.34-19.el9 (bug 2024347). I think this means that we need to verify that the hard-coded constants are still correct on all architectures. I had hoped to avoid that by getting rid of the constants.
Comment 6 Marek Polacek 2022-01-31 17:13:21 UTC 
And if this gets fixed in RHEL 9.0, we can avoid all that verification?  If this is more important than I though, I'm happy to reconsider.
Comment 7 Florian Weimer 2022-01-31 17:20:17 UTC 
(In reply to Marek Polacek from comment #6)
> And if this gets fixed in RHEL 9.0, we can avoid all that verification?

I think so, that's why I'm suggesting it. GCC (the sanitizers) will then just use the constant computed from sizeof (struct pthread) during the glibc build, using glibc's internal definition of struct pthread.

Maybe we should bring this up during tomorrow's cross-team call, given that the sanitizers live more on the LLVM side of things.
Comment 8 Marek Polacek 2022-01-31 17:23:26 UTC 
(In reply to Florian Weimer from comment #7)
> (In reply to Marek Polacek from comment #6)
> > And if this gets fixed in RHEL 9.0, we can avoid all that verification?
> 
> I think so, that's why I'm suggesting it. GCC (the sanitizers) will then
> just use the constant computed from sizeof (struct pthread) during the glibc
> build, using glibc's internal definition of struct pthread.

Ok.
 
> Maybe we should bring this up during tomorrow's cross-team call, given that
> the sanitizers live more on the LLVM side of things.

Sounds good.

Moving back to RHEL 9.0.
Comment 9 Florian Weimer 2022-02-04 17:23:44 UTC 
LLVM upstream patch review: https://reviews.llvm.org/D119007
Comment 10 Marek Polacek 2022-02-08 20:52:30 UTC 
Patch pushed upstream:

commit ef14b78d9a144ba81ba02083fe21eb286a88732b (HEAD -> main, origin/main)
Author: Florian Weimer <fweimer>
Date:   Tue Feb 8 12:46:41 2022 -0800

    [sanitizer] Use _thread_db_sizeof_pthread to obtain struct pthread size
    
    This symbol has been exported (as an internal GLIBC_PRIVATE symbol) from libc.so.6 starting with glibc 2.34. glibc uses it internally for its libthread_db implementation to enable thread debugging on GDB, so it is unlikely to go away for now.
    
    Fixes #52989.
    
    Reviewed By: #sanitizers, MaskRay, vitalybuka
    
    Differential Revision: https://reviews.llvm.org/D119007


I think I'll put it into RHEL 9 gcc now, hoping that eventually it'll be squeezed out when the patch makes its way into Fedora gcc.

Thanks Florian.
Comment 16 errata-xmlrpc 2022-05-17 15:55:42 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (new packages: gcc), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2022:3966
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