riscv: prevent compressed instructions in alternatives

A patch from »riscv: support for Svpbmt and D1 memory types« in state Mainline for linux-kernel

From: Heiko Stuebner <heiko@...> Date: Mon, 10 Jan 2022 19:13:49 +0100

Commit-Message

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@...>

Patch-Comment

arch/riscv/include/asm/alternative-macros.h | 24 +++++++++++++++++++++ 1 file changed, 24 insertions(+)

Statistics

  • 24 lines added
  • 0 lines removed

Changes

----------------- arch/riscv/include/asm/alternative-macros.h ------------------
index 25b4559d743b..3c12396e247c 100644
@@ -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
@@ -72,7 +84,11 @@
".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" \
@@ -81,7 +97,11 @@
#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)
@@ -91,7 +111,11 @@
#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" \
+ ".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)
 
 

Recent Patches

About Us

Sed lacus. Donec lectus. Nullam pretium nibh ut turpis. Nam bibendum. In nulla tortor, elementum vel, tempor at, varius non, purus. Mauris vitae nisl nec metus placerat consectetuer.

Read More...