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Message-ID: <20220725201009.gwuchzswcqaxntrk@pali>
Date: Mon, 25 Jul 2022 22:10:09 +0200
From: Pali Rohár <pali@...nel.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Michael Ellerman <mpe@...erman.id.au>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Regression: Linux v5.15+ does not boot on Freescale P2020
On Monday 25 July 2022 16:20:49 Christophe Leroy wrote:
> Le 25/07/2022 à 14:52, Pali Rohár a écrit :
> > On Monday 25 July 2022 18:20:01 Michael Ellerman wrote:
> >> Pali Rohár <pali@...nel.org> writes:
> >>> On Saturday 23 July 2022 14:42:22 Christophe Leroy wrote:
> >>>> Le 22/07/2022 à 11:09, Pali Rohár a écrit :
> >>>>> Trying to boot mainline Linux kernel v5.15+, including current version
> >>>>> from master branch, on Freescale P2020 does not work. Kernel does not
> >>>>> print anything to serial console, seems that it does not work and after
> >>>>> timeout watchdog reset the board.
> >>>>
> >>>> Can you provide more information ? Which defconfig or .config, which
> >>>> version of gcc, etc ... ?
> >>>
> >>> I used default defconfig for mpc85xx with gcc 8, compilation for e500
> >>> cores.
> >>>
> >>> If you need exact .config content I can send it during week.
> >>>
> >>>>> I run git bisect and it found following commit:
> >>>>>
> >>>>> 9401f4e46cf6965e23738f70e149172344a01eef is the first bad commit
> >>>>> commit 9401f4e46cf6965e23738f70e149172344a01eef
> >>>>> Author: Christophe Leroy <christophe.leroy@...roup.eu>
> >>>>> Date: Tue Mar 2 08:48:11 2021 +0000
> >>>>>
> >>>>> powerpc: Use lwarx/ldarx directly instead of PPC_LWARX/LDARX macros
> >>>>>
> >>>>> Force the eh flag at 0 on PPC32.
> >>>>>
> >>>>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> >>>>> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> >>>>> Link: https://lore.kernel.org/r/1fc81f07cabebb875b963e295408cc3dd38c8d85.1614674882.git.christophe.leroy@csgroup.eu
> >>>>>
> >>>>> :040000 040000 fe6747e45736dfcba74914a9445e5f70f5120600 96358d08b65d3200928a973efb5b969b3d45f2b0 M arch
> >>>>>
> >>>>>
> >>>>> If I revert this commit then kernel boots correctly. It also boots fine
> >>>>> if I revert this commit on top of master branch.
> >>>>>
> >>>>> Freescale P2020 has two 32-bit e500 powerpc cores.
> >>>>>
> >>>>> Any idea why above commit is causing crash of the kernel? And why it is
> >>>>> needed? Could eh flag set to 0 cause deadlock?
> >>>>
> >>>> Setting the eh flag to 0 is not supposed to be a change introduced by
> >>>> that commit. Indeed that commit is not supposed to change anything at
> >>>> all in the generated code.
> >>>
> >>> My understanding of that commit is that it changed eh flag parameter
> >>> from 1 to 0 for 32-bit powerpc, including also p2020.
> >>
> >> Can you compare the disassembly before and after and find a place where
> >> an instruction has changed?
> >>
> >> cheers
> >
> > Yes, of course. Here is diff between output from objdump -d vmlinux.
> > original version --- is from git master branch and modified version +++
> > is the original version with reverted above problematic commit.
> > So the +++ version is the one which is working.
> >
> > --- vmlinux.master.dump 2022-07-25 14:43:45.922239496 +0200
> > +++ vmlinux.revert.dump 2022-07-25 14:43:49.238259296 +0200
> > @@ -1,5 +1,5 @@
> >
> > -vmlinux.master: file format elf32-powerpc
> > +vmlinux.revert: file format elf32-powerpc
> >
> >
> > Disassembly of section .head.text:
> > @@ -11213,7 +11213,7 @@ c000b850: 3f a0 c1 0f lis r29,-1611
> > c000b854: 81 02 00 04 lwz r8,4(r2)
> > c000b858: 3b fd 10 68 addi r31,r29,4200
> > c000b85c: 39 40 00 01 li r10,1
> > -c000b860: 7d 20 f8 29 lwarx r9,0,r31,1
> > +c000b860: 7d 20 f8 28 lwarx r9,0,r31
> > c000b864: 2c 09 00 00 cmpwi r9,0
> > c000b868: 40 82 00 10 bne c000b878 <die+0x68>
> > c000b86c: 7d 40 f9 2d stwcx. r10,0,r31
>
> That's really strange. I made a try with mpc85xx_defconfig with GCC 11
> and I don't get any such difference.
Yes, that is strange...
> Does your version of GCC has anything special ?
Nothing. Ordinary Debian 10 amd64 system with cross compiler from
gcc-powerpc-linux-gnuspe package (standard version, part of Debian).
Now I did again clean test with same Debian 10 cross compiler.
$ git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git && cd linux
$ git checkout v5.15
$ make mpc85xx_smp_defconfig ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnuspe-
$ make vmlinux ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnuspe-
$ cp -a vmlinux vmlinux.v5.15
$ git revert 9401f4e46cf6965e23738f70e149172344a01eef
$ make vmlinux ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnuspe-
$ cp -a vmlinux vmlinux.revert
$ powerpc-linux-gnuspe-objdump -d vmlinux.revert > vmlinux.revert.dump
$ powerpc-linux-gnuspe-objdump -d vmlinux.v5.15 > vmlinux.v5.15.dump
$ diff -Naurp vmlinux.v5.15.dump vmlinux.revert.dump
And there are:
-c000c304: 7d 20 f8 29 lwarx r9,0,r31,1
+c000c304: 7d 20 f8 28 lwarx r9,0,r31
I guess it must be reproducible this issue as I'm using regular
toolchain from distribution.
Just to note that I had to apply Makefile patch for CONFIG_E500
https://lore.kernel.org/linuxppc-dev/20220524093939.30927-1-pali@kernel.org/
But I was told that this issue is reproducible also by OpenWRT non-SPE
gcc 8 toolchain, without using above Makefile patch.
So I have feeling that this is either related to gcc 8 or to binutils.
On that Debian is binutils 2.31.1-16. Or maybe something in .config?
> Can you send you exact .config ?
.config from the above test case is in the attachment.
> Thanks
> Christophe
View attachment ".config" of type "text/plain" (110815 bytes)
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