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Date: Mon, 7 Mar 2022 21:53:04 +0100
From: Heiko Stuebner <heiko@...ech.de>
To: palmer@...belt.com, paul.walmsley@...ive.com, aou@...s.berkeley.edu
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
wefu@...hat.com, liush@...winnertech.com, guoren@...nel.org,
atishp@...shpatra.org, anup@...infault.org, drew@...gleboard.org,
hch@....de, arnd@...db.de, wens@...e.org, maxime@...no.tech,
gfavor@...tanamicro.com, andrea.mondelli@...wei.com,
behrensj@....edu, xinhaoqu@...wei.com, mick@....forth.gr,
allen.baum@...erantotech.com, jscheid@...tanamicro.com,
rtrauben@...il.com, samuel@...lland.org, cmuellner@...ux.com,
philipp.tomsich@...ll.eu, Heiko Stuebner <heiko@...ech.de>
Subject: [PATCH v7 07/13] riscv: prevent compressed instructions in alternatives
Instructions are opportunistically compressed by the RISC-V assembler
when possible, but in alternatives-blocks both the old and new content
need to be the same size, so having the toolchain do somewhat random
optimizations will cause strange side-effects like
"attempt to move .org backwards" compile-time errors.
Already a simple "and" used in alternatives assembly will cause these
mismatched code sizes.
So prevent compressed instructions to be generated in alternatives-
code and use option-push and -pop to only limit this to the relevant
code blocks
Signed-off-by: Heiko Stuebner <heiko@...ech.de>
---
arch/riscv/include/asm/alternative-macros.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
index c0fb11fad631..3a52884bf23d 100644
--- a/arch/riscv/include/asm/alternative-macros.h
+++ b/arch/riscv/include/asm/alternative-macros.h
@@ -19,7 +19,10 @@
.popsection
.subsection 1
888 :
+ .option push
+ .option norvc
\new_c
+ .option pop
889 :
.previous
.org . - (889b - 888b) + (887b - 886b)
@@ -29,7 +32,10 @@
.macro __ALTERNATIVE_CFG old_c, new_c, vendor_id, errata_id, enable
886 :
+ .option push
+ .option norvc
\old_c
+ .option pop
887 :
ALT_NEW_CONTENT \vendor_id, \errata_id, \enable, \new_c
.endm
@@ -40,7 +46,10 @@
.macro __ALTERNATIVE_CFG_2 old_c, new_c_1, vendor_id_1, errata_id_1, enable_1, \
new_c_2, vendor_id_2, errata_id_2, enable_2
886 :
+ .option push
+ .option norvc
\old_c
+ .option pop
887 :
ALT_NEW_CONTENT \vendor_id_1, \errata_id_1, \enable_1, \new_c_1
ALT_NEW_CONTENT \vendor_id_2, \errata_id_2, \enable_2, \new_c_2
@@ -70,7 +79,10 @@
".popsection\n" \
".subsection 1\n" \
"888 :\n" \
+ ".option push\n" \
+ ".option norvc\n" \
new_c "\n" \
+ ".option pop\n" \
"889 :\n" \
".previous\n" \
".org . - (887b - 886b) + (889b - 888b)\n" \
@@ -79,7 +91,10 @@
#define __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, enable) \
"886 :\n" \
+ ".option push\n" \
+ ".option norvc\n" \
old_c "\n" \
+ ".option pop\n" \
"887 :\n" \
ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c)
@@ -89,7 +104,10 @@
#define __ALTERNATIVE_CFG_2(old_c, new_c_1, vendor_id_1, errata_id_1, enable_1, \
new_c_2, vendor_id_2, errata_id_2, enable_2) \
"886 :\n" \
+ ".option push\n" \
+ ".option norvc\n" \
old_c "\n" \
+ ".option pop\n" \
"887 :\n" \
ALT_NEW_CONTENT(vendor_id_1, errata_id_1, enable_1, new_c_1) \
ALT_NEW_CONTENT(vendor_id_2, errata_id_2, enable_2, new_c_2)
--
2.30.2
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