RISC-V 32-bit support

Added 32-bit RISC-V support. I have managed to get 32-bit RISC-V No-MMU
Linux running based on mainstream buildroot. It's nice to have uclibc
support this 32-bit No-MMU target.

There's no substantial code change except definations and config
options.

Signed-off-by: Yimin Gu <ustcymgu@gmail.com>

Rules.mak

@@ -296,6 +296,7 @@ ifneq ($(TARGET_ARCH),c6x)
 ifneq ($(TARGET_ARCH),h8300)
 ifneq ($(TARGET_ARCH),arc)
 ifneq ($(TARGET_ARCH),aarch64)
+ifneq ($(TARGET_ARCH),riscv32)
 CPU_CFLAGS-y += -msoft-float
 endif
 endif
@@ -307,6 +308,7 @@ endif
 endif
 endif
 endif
+endif
 
 ifeq ($(TARGET_ARCH),aarch64)
 CPU_CFLAGS-y += -ftls-model=initial-exec

extra/Configs/Config.in

@@ -39,6 +39,7 @@ choice
 	default TARGET_or1k if DESIRED_TARGET_ARCH = "or1k"
 	default TARGET_powerpc if DESIRED_TARGET_ARCH = "powerpc"
 	default TARGET_riscv64 if DESIRED_TARGET_ARCH = "riscv64"
+	default TARGET_riscv32 if DESIRED_TARGET_ARCH = "riscv32"
 	default TARGET_sh if DESIRED_TARGET_ARCH = "sh"
 	default TARGET_sparc if DESIRED_TARGET_ARCH = "sparc"
 	default TARGET_sparc64 if DESIRED_TARGET_ARCH = "sparc64"
@@ -125,6 +126,9 @@ config TARGET_powerpc
 config TARGET_riscv64
 	bool "riscv64"
 
+config TARGET_riscv32
+	bool "riscv32"
+
 config TARGET_sh
 	bool "superh"
 
@@ -260,6 +264,10 @@ if TARGET_riscv64
 source "extra/Configs/Config.riscv64"
 endif
 
+if TARGET_riscv32
+source "extra/Configs/Config.riscv32"
+endif
+
 if TARGET_sh
 source "extra/Configs/Config.sh"
 endif
@@ -565,6 +573,7 @@ config UCLIBC_HAS_LINUXTHREADS
 	select UCLIBC_HAS_REALTIME
 	depends on !TARGET_aarch64 && \
 		   !TARGET_riscv64 && \
+		   !TARGET_riscv32 && \
 		   !TARGET_metag
 	help
 	  If you want to compile uClibc with Linuxthreads support, then answer Y.

extra/Configs/Config.riscv32

@@ -0,0 +1,14 @@
+#
+# For a description of the syntax of this configuration file,
+# see extra/config/Kconfig-language.txt
+#
+
+config TARGET_ARCH
+	string
+	default "riscv32"
+
+config FORCE_OPTIONS_FOR_ARCH
+	bool
+	default y
+	select ARCH_LITTLE_ENDIAN
+	select ARCH_HAS_MMU

libc/sysdeps/linux/riscv32

@@ -0,0 +1 @@
+riscv64

libc/sysdeps/linux/riscv64/bits/wordsize.h

@@ -25,5 +25,6 @@
 #if __riscv_xlen == 64
 # define __WORDSIZE_TIME64_COMPAT32 1
 #else
-# error "rv32i-based targets are not supported"
+# define __WORDSIZE_TIME64_COMPAT32 1
+// # warning "rv32i-based targets are experimental"
 #endif

libc/sysdeps/linux/riscv64/sys/asm.h

@@ -26,7 +26,11 @@
 # define REG_S sd
 # define REG_L ld
 #elif __riscv_xlen == 32
-# error "rv32i-based targets are not supported"
+# define PTRLOG 2
+# define SZREG    4
+# define REG_S sw
+# define REG_L lw
+// # warning "rv32i-based targets are experimental"
 #else
 # error __riscv_xlen must equal 32 or 64
 #endif