[RFC PATCH V3 02/43] rv64ilp32_abi: riscv: Adapt Makefile and Kconfig

[guoren@kernel.org]

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.org>

Extend the ARCH_RV64I base with ABI_RV64ILP32 to compile the Linux
kernel self into ILP32 on CONFIG_64BIT=y, minimizing the kernel's
memory footprint and cache occupation.

The 'cmd_cpp_lds_S' in scripts/Makefile.build uses cpp_flags for
ld.s generation, so add "-mabi=xxx" to KBUILD_CPPFLAGS, just like
what we've done in KBUILD_CLFAGS and KBUILD_AFLAGS.

cmd_cpp_lds_S = $(CPP) $(cpp_flags) -P -U$(ARCH)

The rv64ilp32 ABI reuses an rv64 toolchain whose default "-mabi="
is lp64, so add "-mabi=ilp32" to correct it.

Add config entry with rv64ilp32.config fragment in Makefile:
 - rv64ilp32_defconfig

Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
---
 arch/riscv/Kconfig                  | 12 ++++++++++--
 arch/riscv/Makefile                 | 17 +++++++++++++++++
 arch/riscv/configs/rv64ilp32.config |  1 +
 3 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 arch/riscv/configs/rv64ilp32.config

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7612c52e9b1e..da2111b0111c 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -213,7 +213,7 @@ config RISCV
 	select TRACE_IRQFLAGS_SUPPORT
 	select UACCESS_MEMCPY if !MMU
 	select USER_STACKTRACE_SUPPORT
-	select ZONE_DMA32 if 64BIT
+	select ZONE_DMA32 if 64BIT && !ABI_RV64ILP32
 
 config RUSTC_SUPPORTS_RISCV
 	def_bool y
@@ -298,6 +298,7 @@ config PAGE_OFFSET
 config KASAN_SHADOW_OFFSET
 	hex
 	depends on KASAN_GENERIC
+	default 0x70000000 if ABI_RV64ILP32
 	default 0xdfffffff00000000 if 64BIT
 	default 0xffffffff if 32BIT
 
@@ -341,7 +342,7 @@ config FIX_EARLYCON_MEM
 
 config ILLEGAL_POINTER_VALUE
 	hex
-	default 0 if 32BIT
+	default 0 if 32BIT || ABI_RV64ILP32
 	default 0xdead000000000000 if 64BIT
 
 config PGTABLE_LEVELS
@@ -418,6 +419,13 @@ config ARCH_RV64I
 
 endchoice
 
+config ABI_RV64ILP32
+	bool "ABI RV64ILP32"
+	depends on 64BIT
+	help
+	  Compile linux kernel self into RV64ILP32 ABI of RISC-V psabi
+	  specification.
+
 # We must be able to map all physical memory into the kernel, but the compiler
 # is still a bit more efficient when generating code if it's setup in a manner
 # such that it can only map 2GiB of memory.
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 13fbc0f94238..76db01020a22 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -30,10 +30,21 @@ ifeq ($(CONFIG_ARCH_RV64I),y)
 	BITS := 64
 	UTS_MACHINE := riscv64
 
+ifeq ($(CONFIG_ABI_RV64ILP32),y)
+	KBUILD_CPPFLAGS += -mabi=ilp32
+
+	KBUILD_CFLAGS += -mabi=ilp32
+	KBUILD_AFLAGS += -mabi=ilp32
+
+	KBUILD_LDFLAGS += -melf32lriscv
+else
+	KBUILD_CPPFLAGS += -mabi=lp64
+
 	KBUILD_CFLAGS += -mabi=lp64
 	KBUILD_AFLAGS += -mabi=lp64
 
 	KBUILD_LDFLAGS += -melf64lriscv
+endif
 
 	KBUILD_RUSTFLAGS += -Ctarget-cpu=generic-rv64 --target=riscv64imac-unknown-none-elf \
 			    -Cno-redzone
@@ -41,6 +52,8 @@ else
 	BITS := 32
 	UTS_MACHINE := riscv32
 
+	KBUILD_CPPFLAGS += -mabi=ilp32
+
 	KBUILD_CFLAGS += -mabi=ilp32
 	KBUILD_AFLAGS += -mabi=ilp32
 	KBUILD_LDFLAGS += -melf32lriscv
@@ -224,6 +237,10 @@ PHONY += rv32_nommu_virt_defconfig
 rv32_nommu_virt_defconfig:
 	$(Q)$(MAKE) -f $(srctree)/Makefile nommu_virt_defconfig 32-bit.config
 
+PHONY += rv64ilp32_defconfig
+rv64ilp32_defconfig:
+	$(Q)$(MAKE) -f $(srctree)/Makefile defconfig rv64ilp32.config
+
 define archhelp
   echo  '  Image		- Uncompressed kernel image (arch/riscv/boot/Image)'
   echo  '  Image.gz	- Compressed kernel image (arch/riscv/boot/Image.gz)'
diff --git a/arch/riscv/configs/rv64ilp32.config b/arch/riscv/configs/rv64ilp32.config
new file mode 100644
index 000000000000..07536586e169
--- /dev/null
+++ b/arch/riscv/configs/rv64ilp32.config
@@ -0,0 +1 @@
+CONFIG_ABI_RV64ILP32=y
-- 
2.40.1