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SubjectRe: [PATCH 5/8] s390/purgatory: workaround llvm's IAS limitations
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
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