linux-kernel - [PATCH 4/8] s390/entry: workaround llvm's IAS limitations

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Date:   Wed, 11 May 2022 14:05:28 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Jonas Paulsson <paulsson@...ux.vnet.ibm.com>,
        Ulrich Weigand <ulrich.weigand@...ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexander Egorenkov <egorenar@...ux.ibm.com>
Cc:     Sven Schnelle <svens@...ux.ibm.com>,
        Andreas Krebbel <krebbel@...ux.ibm.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: [PATCH 4/8] s390/entry: workaround llvm's IAS limitations

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

<instantiation>:3:13: error: invalid operand for instruction
 clgfi %r14,.Lsie_done - .Lsie_gmap

Workaround this by adding clang specific code which reads the specific
value from memory. Since this code is within the hot paths of the kernel
and adds an additional memory reference, keep the original code, and add
ifdef'ed code.

Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
---
 arch/s390/kernel/entry.S | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index e1664b45090f..ff7a75078e93 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -171,8 +171,19 @@ _LPP_OFFSET	= __LC_LPP
 	.macro OUTSIDE reg,start,end,outside_label
 	larl	%r14,\start
 	slgrk	%r14,\reg,%r14
+#ifdef CONFIG_CC_IS_CLANG
+	clgfrl	%r14,.Lrange_size\@
+#else
 	clgfi	%r14,\end - \start
+#endif
 	jhe	\outside_label
+#ifdef CONFIG_CC_IS_CLANG
+	.section .rodata, "a"
+	.align 4
+.Lrange_size\@:
+	.long	\end - \start
+	.previous
+#endif
 	.endm
 
 	.macro SIEEXIT
-- 
2.32.0