[PATCH 06/12] riscv: prevent compressed instructions in alternatives

Heiko Stuebner
2022-05-11T19:30:07Z

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@sntech.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
---
arch/riscv/include/asm/alternative-macros.h | 24 +++++++++++++++++++++
1 file changed, 24 insertions(+)

diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
index 8c2bbc7bbe50..e13b1f6bb400 100644
--- a/arch/riscv/include/asm/alternative-macros.h
+++ b/arch/riscv/include/asm/alternative-macros.h
@@ -21,7 +21,11 @@
.popsection
.subsection 1
888 :
+ .option push
+ .option norvc
+ .option norelax
\new_c
+ .option pop
889 :
.previous
.org . - (889b - 888b) + (887b - 886b)
@@ -31,7 +35,11 @@

.macro __ALTERNATIVE_CFG old_c, new_c, vendor_id, errata_id, enable
886 :
+ .option push
+ .option norvc
+ .option norelax
\old_c
+ .option pop
887 :
ALT_NEW_CONTENT \vendor_id, \errata_id, \enable, \new_c
.endm
@@ -42,7 +50,11 @@
.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
+ .option norelax
\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
@@ -76,7 +88,11 @@
".popsection\n" \
".subsection 1\n" \
"888 :\n" \
+ ".option push\n" \
+ ".option norvc\n" \
+ ".option norelax\n" \
new_c "\n" \
+ ".option pop\n" \
"889 :\n" \
".previous\n" \
".org . - (887b - 886b) + (889b - 888b)\n" \
@@ -85,7 +101,11 @@

#define __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, enable) \
"886 :\n" \
+ ".option push\n" \
+ ".option norvc\n" \
+ ".option norelax\n" \
old_c "\n" \
+ ".option pop\n" \
"887 :\n" \
ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c)

@@ -97,7 +117,11 @@
new_c_2, vendor_id_2, errata_id_2, \
enable_2) \
"886 :\n" \
+ ".option push\n" \
+ ".option norvc\n" \
+ ".option norelax\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)
--
2.35.1