[PATCH 01/13] openrisc: Add gcc machine instruction flag configuration

Stafford Horne
2022-05-15T12:42:14Z

OpenRISC GCC supports flags to enable the backend to output instructions
if they are supported by a target processor. This patch adds
configuration flags to enable configuring these flags to tune the kernel
for a particular CPU configuration.

In the future we could also enable all of these flags by default and
provide instruction emulation in the kernel to make these choices easier
for users but this is what we provide for now.

Signed-off-by: Stafford Horne <shorne@gmail.com>
---
arch/openrisc/Kconfig | 53 ++++++++++++++++++++++++++++++++++++++++++
arch/openrisc/Makefile | 17 ++++++++++++++
2 files changed, 70 insertions(+)

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index 0d68adf6e02b..ea7eac20911a 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -114,6 +114,59 @@ config OPENRISC_HAVE_INST_DIV
default y
help
Select this if your implementation has a hardware divide instruction
+
+config OPENRISC_HAVE_INST_CMOV
+ bool "Have instruction l.cmov for conditional move"
+ default y
+ help
+ This config enables gcc to generate l.cmov instructions when compiling
+ the kernel which in general will improve performance and reduce the
+ binary size.
+
+ Select this if your implementation has support for the Class II
+ l.cmov conistional move instruction.
+
+ Say N if you are unsure.
+
+config OPENRISC_HAVE_INST_ROR
+ bool "Have instruction l.ror for rotate right"
+ default y
+ help
+ This config enables gcc to generate l.ror instructions when compiling
+ the kernel which in general will improve performance and reduce the
+ binary size.
+
+ Select this if your implementation has support for the Class II
+ l.ror rotate right instruction.
+
+ Say N if you are unsure.
+
+config OPENRISC_HAVE_INST_RORI
+ bool "Have instruction l.rori for rotate right with immediate"
+ default y
+ help
+ This config enables gcc to generate l.rori instructions when compiling
+ the kernel which in general will improve performance and reduce the
+ binary size.
+
+ Select this if your implementation has support for the Class II
+ l.rori rotate right with immediate instruction.
+
+ Say N if you are unsure.
+
+config OPENRISC_HAVE_INST_SEXT
+ bool "Have instructions l.ext* for sign extension"
+ default y
+ help
+ This config enables gcc to generate l.ext* instructions when compiling
+ the kernel which in general will improve performance and reduce the
+ binary size.
+
+ Select this if your implementation has support for the Class II
+ l.exths, l.extbs, l.exthz and l.extbz size extend instructions.
+
+ Say N if you are unsure.
+
endmenu

config NR_CPUS
diff --git a/arch/openrisc/Makefile b/arch/openrisc/Makefile
index 760b734fb822..b446510173cd 100644
--- a/arch/openrisc/Makefile
+++ b/arch/openrisc/Makefile
@@ -21,6 +21,7 @@ OBJCOPYFLAGS := -O binary -R .note -R .comment -S
LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)

KBUILD_CFLAGS += -pipe -ffixed-r10 -D__linux__
+KBUILD_CFLAGS += -msfimm -mshftimm

all: vmlinux.bin

@@ -38,6 +39,22 @@ else
KBUILD_CFLAGS += $(call cc-option,-msoft-div)
endif

+ifeq ($(CONFIG_OPENRISC_HAVE_INST_CMOV),y)
+ KBUILD_CFLAGS += $(call cc-option,-mcmov)
+endif
+
+ifeq ($(CONFIG_OPENRISC_HAVE_INST_ROR),y)
+ KBUILD_CFLAGS += $(call cc-option,-mror)
+endif
+
+ifeq ($(CONFIG_OPENRISC_HAVE_INST_RORI),y)
+ KBUILD_CFLAGS += $(call cc-option,-mrori)
+endif
+
+ifeq ($(CONFIG_OPENRISC_HAVE_INST_SEXT),y)
+ KBUILD_CFLAGS += $(call cc-option,-msext)
+endif
+
head-y := arch/openrisc/kernel/head.o

libs-y += $(LIBGCC)
--
2.31.1