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Date:   Thu, 12 May 2022 19:25:38 +0200
From:   Heiko Carstens <hca@linux.ibm.com>
To:     Heiko Carstens <hca@linux.ibm.com>
Cc:     Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Jonas Paulsson <paulsson@linux.vnet.ibm.com>,
        Ulrich Weigand <ulrich.weigand@de.ibm.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Alexander Egorenkov <egorenar@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Andreas Krebbel <krebbel@linux.ibm.com>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org
Subject: Re: [PATCH 5/8] s390/purgatory: workaround llvm's IAS limitations
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References: <20220511120532.2228616-1-hca@linux.ibm.com>
 <20220511120532.2228616-6-hca@linux.ibm.com>
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On Wed, May 11, 2022 at 02:05:29PM +0200, Heiko Carstens wrote:
> llvm's integrated assembler cannot handle immediate values which are
> calculated with two local labels:
> 
> arch/s390/purgatory/head.S:139:11: error: invalid operand for instruction
>  aghi %r8,-(.base_crash-purgatory_start)
> 
> Workaround this by partially rewriting the code.
> 
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
>  arch/s390/purgatory/head.S | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
...
> -	aghi	%r10,stack-purgatory_start
> +	larl	%r0,purgatory_start
> +	slgrk	%r0,%r7,%r0
> +	agr	%r10,%r0

Same problem here: slgrk does not work for MARCH=z10. So new version
looks like:

From 99e011fa48d9fe90f6d3d58cf89f738afddf394f Mon Sep 17 00:00:00 2001
From: Heiko Carstens <hca@linux.ibm.com>
Date: Sat, 7 May 2022 20:08:55 +0200
Subject: [PATCH 4/7] s390/purgatory: workaround llvm's IAS limitations

llvm's integrated assembler cannot handle immediate values which are
calculated with two local labels:

arch/s390/purgatory/head.S:139:11: error: invalid operand for instruction
 aghi %r8,-(.base_crash-purgatory_start)

Workaround this by partially rewriting the code.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
 arch/s390/purgatory/head.S | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/arch/s390/purgatory/head.S b/arch/s390/purgatory/head.S
index 3d1c31e0cf3d..6f835124ee82 100644
--- a/arch/s390/purgatory/head.S
+++ b/arch/s390/purgatory/head.S
@@ -44,11 +44,14 @@
 .endm
 
 .macro MEMSWAP dst,src,buf,len
-10:	cghi	\len,bufsz
+10:	larl	%r0,purgatory_end
+	larl	%r1,stack
+	slgr	%r0,%r1
+	cgr	\len,%r0
 	jh	11f
 	lgr	%r4,\len
 	j	12f
-11:	lghi	%r4,bufsz
+11:	lgr	%r4,%r0
 
 12:	MEMCPY	\buf,\dst,%r4
 	MEMCPY	\dst,\src,%r4
@@ -135,12 +138,18 @@ ENTRY(purgatory_start)
 
 .start_crash_kernel:
 	/* Location of purgatory_start in crash memory */
+	larl	%r0,.base_crash
+	larl	%r1,purgatory_start
+	slgr	%r0,%r1
 	lgr	%r8,%r13
-	aghi	%r8,-(.base_crash-purgatory_start)
+	sgr	%r8,%r0
 
 	/* Destination for this code i.e. end of memory to be swapped. */
+	larl	%r0,purgatory_end
+	larl	%r1,purgatory_start
+	slgr	%r0,%r1
 	lg	%r9,crash_size-.base_crash(%r13)
-	aghi	%r9,-(purgatory_end-purgatory_start)
+	sgr	%r9,%r0
 
 	/* Destination in crash memory, i.e. same as r9 but in crash memory. */
 	lg	%r10,crash_start-.base_crash(%r13)
@@ -149,15 +158,19 @@ ENTRY(purgatory_start)
 	/* Buffer location (in crash memory) and size. As the purgatory is
 	 * behind the point of no return it can re-use the stack as buffer.
 	 */
-	lghi	%r11,bufsz
+	larl	%r11,purgatory_end
 	larl	%r12,stack
+	slgr	%r11,%r12
 
 	MEMCPY	%r12,%r9,%r11	/* dst	-> (crash) buf */
 	MEMCPY	%r9,%r8,%r11	/* self -> dst */
 
 	/* Jump to new location. */
 	lgr	%r7,%r9
-	aghi	%r7,.jump_to_dst-purgatory_start
+	larl	%r0,.jump_to_dst
+	larl	%r1,purgatory_start
+	slgr	%r0,%r1
+	agr	%r7,%r0
 	br	%r7
 
 .jump_to_dst:
@@ -169,7 +182,10 @@ ENTRY(purgatory_start)
 
 	/* Load new buffer location after jump */
 	larl	%r7,stack
-	aghi	%r10,stack-purgatory_start
+	lgr	%r0,%r7
+	larl	%r1,purgatory_start
+	slgr	%r0,%r1
+	agr	%r10,%r0
 	MEMCPY	%r10,%r7,%r11	/* (new) buf -> (crash) buf */
 
 	/* Now the code is set up to run from its designated location. Start
-- 
2.32.0