feat(build): march option selection
Current build infra uses ARM_ARCH_MAJOR/MINOR to come up with march
version and uses that march version with the compiler.
However in certain situations this is not ideal, like for example when
we build with gcc-11 which supports only till march=armv8.5 but
we need to build for 8.8 build, this means we need to bump down
MAJOR/MINOR and we can't rely on major and minor values from the
platform to select march value and build infra doesn't even try
to compile and fails with not supported MAJOR/MINOR.
By adding a march build helper we try to check if compiler supports
given march value from MAJOR/MINOR values from platform, if compiler
doesn't support then we try to check what's the max or best supported
march version by compiler and choose that march value and try to
compile with that.
This is a supportive mechanism which will decouple march reliance on
MAJOR/MINOR values from platform and will pave way for setting up
enabling of features based on MAJOR/MINOR without worrying about the
compiler not supporting given MAJOR/MINOR.
Also in TF-A we use generic instructions without much reliance or need
for exact march necessity. So enabling and building features from
armv-8.8 using an armv-8.5 march value is still going to be fine.
Please note: Platforms are free to freeze their march values using
`MARCH_DIRECTIVE`. In absence of this define we are going to poke
the compiler and come up with a potential march value.
Change-Id: I673061a269ec9018ff12e75dc375979f5e33b7d1
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/Makefile b/Makefile
index 8a0a2e0..f33a12e 100644
--- a/Makefile
+++ b/Makefile
@@ -220,14 +220,6 @@
# Will set march-directive from platform configuration
else
target32-directive = -target armv8a-none-eabi
-
-# Set the compiler's target architecture profile based on
-# ARM_ARCH_MAJOR ARM_ARCH_MINOR options
- ifeq (${ARM_ARCH_MINOR},0)
- march-directive = -march=armv${ARM_ARCH_MAJOR}-a
- else
- march-directive = -march=armv${ARM_ARCH_MAJOR}.${ARM_ARCH_MINOR}-a
- endif #(ARM_ARCH_MINOR)
endif #(ARM_ARCH_MAJOR)
################################################################################
@@ -279,12 +271,12 @@
ifneq ($(findstring clang,$(notdir $(CC))),)
ifneq ($(findstring armclang,$(notdir $(CC))),)
- TF_CFLAGS_aarch32 := -target arm-arm-none-eabi $(march-directive)
- TF_CFLAGS_aarch64 := -target aarch64-arm-none-eabi $(march-directive)
+ TF_CFLAGS_aarch32 := -target arm-arm-none-eabi
+ TF_CFLAGS_aarch64 := -target aarch64-arm-none-eabi
LD := $(LINKER)
else
- TF_CFLAGS_aarch32 = $(target32-directive) $(march-directive)
- TF_CFLAGS_aarch64 := -target aarch64-elf $(march-directive)
+ TF_CFLAGS_aarch32 = $(target32-directive)
+ TF_CFLAGS_aarch64 := -target aarch64-elf
LD := $(shell $(CC) --print-prog-name ld.lld)
AR := $(shell $(CC) --print-prog-name llvm-ar)
@@ -296,8 +288,6 @@
PP := $(CC) -E $(TF_CFLAGS_$(ARCH))
AS := $(CC) -c -x assembler-with-cpp $(TF_CFLAGS_$(ARCH))
else ifneq ($(findstring gcc,$(notdir $(CC))),)
- TF_CFLAGS_aarch32 = $(march-directive)
- TF_CFLAGS_aarch64 = $(march-directive)
ifeq ($(ENABLE_LTO),1)
# Enable LTO only for aarch64
ifeq (${ARCH},aarch64)
@@ -308,8 +298,6 @@
endif
LD = $(LINKER)
else
- TF_CFLAGS_aarch32 = $(march-directive)
- TF_CFLAGS_aarch64 = $(march-directive)
LD = $(LINKER)
endif #(clang)
@@ -671,6 +659,14 @@
include ${PLAT_MAKEFILE_FULL}
+################################################################################
+# Platform specific Makefile might provide us ARCH_MAJOR/MINOR use that to come
+# up with appropriate march values for compiler.
+################################################################################
+include ${MAKE_HELPERS_DIRECTORY}march.mk
+
+TF_CFLAGS += $(march-directive)
+
# This internal flag is common option which is set to 1 for scenarios
# when the BL2 is running in EL3 level. This occurs in two scenarios -
# 4 world system running BL2 at EL3 and two world system without BL1 running
diff --git a/make_helpers/march.mk b/make_helpers/march.mk
new file mode 100644
index 0000000..2417709
--- /dev/null
+++ b/make_helpers/march.mk
@@ -0,0 +1,85 @@
+#
+# Copyright (c) 2023, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+# This build helper makefile is used to determine a suitable march build
+# option to be used, based on platform provided ARM_ARCH_MAJOR/MINOR
+# data and compiler supported march version.
+
+# Set the compiler's target architecture profile based on
+# ARM_ARCH_MAJOR and ARM_ARCH_MINOR options.
+
+
+# This is used to collect available march values from compiler.
+# Example on a gcc-12.2 arm64 toolchain it will look like:
+# [...]
+#./aarch64-none-elf-gcc --target-help -march=foo
+# cc1: error: unknown value 'foo' for '-march'
+# cc1: note: valid arguments are: armv8-a armv8.1-a armv8.2-a armv8.3-a armv8.4-a armv8.5-a
+# armv8.6-a armv8.7-a armv8.8-a armv8-r armv9-a
+# [...]
+#
+GCC_MARCH_OUTPUT := $(shell $(CC) -march=foo -Q --help=target -v 2>&1)
+
+# This function is used to find the best march value supported by the given compiler.
+# We try to use `GCC_MARCH_OUTPUT` which has verbose message with supported march values we filter that
+# to find armvX.Y-a or armvX-a values, then filter the best supported arch based on ARM_ARCH_MAJOR.
+#
+# Example on a gcc-12.2 arm64 toolchain this will return armv9-a if platform requested for armv9.2-a
+# Similarly on gcc 11.3 it would return armv8.6-a if platform requested armv8.8-a
+define major_best_avail_march
+$(1) := $(lastword $(filter armv$(ARM_ARCH_MAJOR)% ,$(filter armv%-a, $(GCC_MARCH_OUTPUT))))
+endef
+
+# This function is used to just return latest march value supported by the given compiler.
+#
+# Example: this would return armv8.6-a on a gcc-11.3 when platform requested for armv9.0-a
+#
+# Thus this function should be used in conjunction with major_best_avail_march, when best match
+# is not found it should be ok to try with lastest known supported march value from the
+# compiler.
+define latest_match_march
+$(1) := $(lastword $(filter armv%-a, $(GCC_MARCH_OUTPUT)))
+endef
+
+ifdef MARCH_DIRECTIVE
+ march-directive := $(MARCH_DIRECTIVE)
+else
+
+ifeq (${ARM_ARCH_MINOR},0)
+ provided-march = armv${ARM_ARCH_MAJOR}-a
+else
+ provided-march = armv${ARM_ARCH_MAJOR}.${ARM_ARCH_MINOR}-a
+endif
+
+ifeq ($(findstring clang,$(notdir $(CC))),)
+
+# We expect from Platform to provide a correct Major/Minor value but expecting something
+# from compiler with unsupported march means we shouldn't fail without trying anything,
+# so here we try to find best supported march value and use that for compilation.
+# If we don't support current march version from gcc compiler, try with lower arch based on
+# availability. In TF-A there is no hard rule for need of higher version march for basic
+# functionality, denying a build on only this fact doesn't look correct, so try with best
+# or latest march values from whats available from compiler.
+ifeq (,$(findstring $(provided-march), $(GCC_MARCH_OUTPUT)))
+ $(eval $(call major_best_avail_march, available-march))
+
+ifeq (, $(available-march))
+ $(eval $(call latest_match_march, available-march))
+endif
+
+# If we fail to come up with any available-march value so far, don't update
+# provided-march and thus allow the build to fail using the provided-march
+# which is derived based on arch_major and arch_minor values.
+ifneq (,$(available-march))
+ provided-march := ${available-march}
+endif
+
+endif # provided-march supported
+endif # not clang
+
+march-directive := -march=${provided-march}
+
+endif # MARCH_DIRECTIVE