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From: "romain.naour at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/98784] New: [gcc 8.4/9.3/10] sparcv8 regression
Date: Thu, 21 Jan 2021 22:13:09 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98784

            Bug ID: 98784
           Summary: [gcc 8.4/9.3/10] sparcv8 regression
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: romain.naour at gmail dot com
  Target Milestone: ---

Hello,

When building a rootfs for sparcv8 using the Buildroot defconfig
qemu_sparc_ss10_defconfig, the system produce some illegal instruction
messages.

gcc 8.3, 9.2 are the latest working gcc version.
git bisect between gcc 8.3 and 8.4 allowed to identify the commit that
introduced the regression:

https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dcommit;h=3D0a83f1a441d7aaadecb368c=
237b6ee70bd7b91d6

The commit has been introduced to fix the following bub:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D92095

It has been backported to gcc 8.4 and 9.3.

Reverting this patch allowed to produce a working rootfs.

This issue can be reproduced using the following steps:

$ git://git.busybox.net/buildroot
$ cd buildroot/
$ git checkout 2020.11.1
$ make qemu_sparc_ss10_defconfig
$ make
$ ./output/images/start-qemu.sh

The kernel boot correctly but the login program (busybox) crash while tryin=
g to
login:

[...]
Starting syslogd:=20
Welcome to Buildroot
buildroot login: root

Welcome to Buildroot
buildroot login: root


For now, It's just a basic test that allow to reproduce the issue.

We can use a shell instead of init program but even with a simple command s=
uch
'ls' the system crash:

sh-5.0# ls

CPU: 0 PID: 1 Comm: sh Not tainted 4.19.16 #1
[f0022fbc :=20
do_exit+0x948/0x968 ]=20
[f000afec :=20
do_signal+0x5f8/0x79c ]=20
[f000b4b4 :=20
do_notify_resume+0x48/0x58 ]=20
[f0008c88 :=20
signal_p+0x14/0x24 ]=20
[0004b874 :=20
0x4b874 ]

Kernel panic - not syncing: Attempted to kill init! exitcode=3D0x00000004

Best regards,
Romain=