riscv: Support standalone

Run hello_world successfully.

U-Boot 2018.01-rc2-00033-gb265b91-dirty (Dec 22 2017 - 13:54:21 +0800)

DRAM:  1 GiB
MMC:   mmc@f0e00000: 0
SF: Detected mx25u1635e with page size 256 Bytes, erase size 4 KiB, total 2 MiB
In:    serial@f0300000
Out:   serial@f0300000
Err:   serial@f0300000
Net:
Warning: mac@e0100000 (eth0) using random MAC address - 0a:47:9b:f8:b4:f2
eth0: mac@e0100000
RISC-V # mmc rescan
RISC-V # fatls mmc 0:1
318907   u-boot-ae250-64.bin
1252   hello_world_ae250_32.bin
328787   u-boot-ae250-32.bin

3 file(s), 0 dir(s)

RISC-V # fatload mmc 0:1 0x600000 hello_world_ae250_32.bin
reading hello_world_ae250_32.bin
1252 bytes read in 23 ms (52.7 KiB/s)
RISC-V # go 0x600000
Example expects ABI version 9
Actual U-Boot ABI version 9
Hello World
argc = 1
argv[0] = "0x600000"
argv[1] = "$B@"
Hit any key to exit ...

RISC-V #

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Signed-off-by: Greentime Hu <green.hu@gmail.com>

examples/standalone/riscv.lds

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2017 Andes Technology Corporation
+ * Rick Chen, Andes Technology Corporation <rick@andestech.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ */
+
+OUTPUT_ARCH(riscv)
+ENTRY(_start)
+SECTIONS
+{
+    . = ALIGN(4);
+    .text :
+    {
+        *(.text)
+    }
+
+    . = ALIGN(4);
+    .data : {
+			__global_pointer$ = . + 0x800;
+			*(.data)
+		}
+
+    . = ALIGN(4);
+
+    .got : {
+        __got_start = .;
+        *(.got)
+        __got_end = .;
+    }
+
+     . = ALIGN(4);
+    __bss_start = .;
+    .bss : { *(.bss) }
+    __bss_end = .;
+
+    . = ALIGN(4);
+    .rela.text : { *(.rela.text .rela.text.* .rela.gnu.linkonce.t.*) }
+
+    _end = .;
+}

examples/standalone/stubs.c

@@ -172,6 +172,18 @@ gd_t *global_data;
 "	lwi	$r16, [$r16 + (%1)]\n"	\
 "	jr	$r16\n"			\
 	: : "i"(offsetof(gd_t, jt)), "i"(FO(x)) : "$r16");
+#elif defined(CONFIG_RISCV)
+/*
+ * t7 holds the pointer to the global_data. gp is call clobbered.
+ */
+#define EXPORT_FUNC(f, a, x, ...)	\
+	asm volatile (			\
+"	.globl " #x "\n"		\
+#x ":\n"				\
+"	lw	x19, %0(gp)\n"		\
+"	lw	x19, %1(x19)\n"		\
+"	jr	x19\n"			\
+	: : "i"(offsetof(gd_t, jt)), "i"(FO(x)) : "x19");
 #elif defined(CONFIG_ARC)
 /*
  * r25 holds the pointer to the global_data. r10 is call clobbered.