Unverified Commit 49b290e4 authored by Heiko Stuebner's avatar Heiko Stuebner Committed by Palmer Dabbelt
Browse files

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: default avatarHeiko Stuebner <heiko@sntech.de>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarPhilipp Tomsich <philipp.tomsich@vrull.eu>
Link: https://lore.kernel.org/r/20220511192921.2223629-7-heiko@sntech.de


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent e509204a

arch/riscv/include/asm/alternative-macros.h

+24 −0
Original line number Diff line number Diff line
@@ -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)