[Bug 1887974] [NEW] [20.04] Valgrind: PPC sync instruction L field should only be 2 bits in ISA 3.0

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---Problem Description---
This is a bug report for focal.

Valgrind, including version 3.16, mishandles the L field of the sync instruction.
More details are available at: https://bugs.kde.org/show_bug.cgi?id=422677

This is a request to backport the following Valgrind patch from
upstream:

commit fb6f7abcbc92506d302fb18a2c5fc853d2929248
Author: Carl Love <cel at us.ibm.com>
Date:   Tue Jun 9 10:42:03 2020 -0500

    Power PC Fix extraction of the L field for sync instruction
    
    The L field is currently a two bit[22:21] field in ISA 3.0. The size of the
    L field has changed over time.
    
    Currently the ISA 3.0 Valgrind sync instruction support code sets the
    flag_L for the instruction L field to a five bit value that includes bits
    that are marked reserved the sync instruction.  This patch fixes the issue for ISA 3.0
    to only setting flag_L the specified two bits.
    
    Valgrind bugzilla:   https://bugs.kde.org/show_bug.cgi?id=422677
 
Contact Information = Tulio Magno/tuliom at linux.ibm.com 
 
---uname output---
N/A
 
Machine Type = Reproducible on all POWER8 and POWER9 servers 
 
---Debugger---
A debugger is not configured
 
---Steps to Reproduce---
 $ cat test-sync.c 
#define __SYNC(l) ".long (0x7c0004AC | ((" #l ") << 21))"

int
main ()
{
        asm volatile(__SYNC(4) : : : "memory");
}
$ gcc test-sync.c && valgrind --tool=none ./a.out
==150073== Nulgrind, the minimal Valgrind tool
==150073== Copyright (C) 2002-2017, and GNU GPL'd, by Nicholas Nethercote.
==150073== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==150073== Command: ./a.out
==150073== 
dis_memsync(ppc)(sync/lwsync,flag_L)
disInstr(ppc): unhandled instruction: 0x7C8004AC
                 primary 31(0x1F), secondary 1196(0x4AC)
==150073== valgrind: Unrecognised instruction at address 0x180788.
==150073==    at 0x180788: main (in /home/tuliom/tmp/a.out)
==150073== Your program just tried to execute an instruction that Valgrind
==150073== did not recognise.
...
 
Userspace tool common name: Valgrind 
 
The userspace tool has the following bit modes: 64-bit 

Userspace deb: valgrind

Userspace tool obtained from project website:  na

** Affects: ubuntu-power-systems
     Importance: Medium
     Assignee: Canonical Foundations Team (canonical-foundations)
         Status: Triaged

** Affects: valgrind (Ubuntu)
     Importance: Undecided
     Assignee: Canonical Foundations Team (canonical-foundations)
         Status: Fix Released

** Affects: valgrind (Ubuntu Bionic)
     Importance: Undecided
     Assignee: Matthieu Clemenceau (mclemenceau)
         Status: In Progress

** Affects: valgrind (Ubuntu Focal)
     Importance: Undecided
     Assignee: Matthieu Clemenceau (mclemenceau)
         Status: In Progress


** Tags: architecture-ppc64le bugnameltc-186878 severity-medium targetmilestone-inin20041
-- 
[20.04] Valgrind: PPC sync instruction L field should only be 2 bits in ISA 3.0
https://bugs.launchpad.net/bugs/1887974
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