Add Riscv Example (#1268)

Add Riscv example. Risc-V CI. Install baremetal toolchain. Prevent imported crt file from messing up linker search.

.github/workflows/main.yml

@@ -319,6 +319,15 @@ jobs:
           cd resources/testfragments
           ../../build/c3c compile --reloc=none --target wasm32 -g0 --link-libc=no --no-entry -Os wasm4.c3
 
+      - name: Install QEMU and Risc-V toolchain
+        run: |
+          sudo apt-get install opensbi qemu-system-misc u-boot-qemu gcc-riscv64-unknown-elf
+
+      - name: Compile and run Baremetal Risc-V Example
+        run: |
+          cd resources/examples/embedded/riscv-qemu
+          make C3C_PATH=../../../../build/ run
+
       - name: Build testproject direct linker
         run: |
           cd resources/testproject

resources/examples/embedded/riscv-qemu/Makefile

@@ -0,0 +1,21 @@
+SRCS_C3 := $(wildcard *.c3)
+
+default: hello.elf
+
+hello.a: $(SRCS_C3)
+	$(C3C_PATH)c3c --use-stdlib=no --no-entry --target elf-riscv32 static-lib $(SRCS_C3)
+
+start.o: start.s
+	riscv64-unknown-elf-as -g -march=rv32i -mabi=ilp32 -misa-spec=20191213 -o start.o start.s
+
+hello.elf: hello.a start.o baremetal.ld
+	riscv64-unknown-elf-ld -T baremetal.ld -m elf32lriscv -o hello.elf hello.a start.o
+
+run: hello.elf
+	qemu-system-riscv32 -nographic -serial mon:stdio -machine virt -semihosting -bios hello.elf
+
+debug: hello.elf
+	qemu-system-riscv32 -nographic -serial mon:stdio -machine virt -semihosting -s -S -bios hello.elf
+
+clean:
+	rm -f *.o *.a hello.elf

resources/examples/embedded/riscv-qemu/README.md

@@ -0,0 +1,8 @@
+# Risc-V 32 Embedded Example With QEMU
+## Prereqs
+- QEMU
+- Risc-V toolchain
+- C3C
+- Make
+## Running
+`make run`

resources/examples/embedded/riscv-qemu/baremetal.ld

@@ -0,0 +1,14 @@
+EXTERN(main)
+
+SECTIONS
+{
+  . = 0x80000000;													/* QEMU default load address to run bios */
+  .text : {
+		KEEP(*(.text._start));								/* Ensure _start is placed first */
+		*(.text*);														/* Program code here */
+	}
+	. = ALIGN (CONSTANT (COMMONPAGESIZE));	/* Make sure linker does not jam data into text section, making text writable */
+  .data : { 
+		*(.data*)															/* Stack goes here */
+	}
+}

resources/examples/embedded/riscv-qemu/hello.c3

@@ -0,0 +1,11 @@
+import uart;
+import semihost;
+
+const UART0_BASE = 0x10000000;
+
+fn void main() @export("main") {
+  Uart* uart0 = (Uart*)UART0_BASE;               // Create pointer to UART 0
+	uart0.fcr = uart::UARTFCR_FFENA;               // Enable FIFO
+  uart0.puts("Hello World!\n");                  // Write the string to the UART
+  semihost::exit(0);                             // Semihosting call to exit host
+}

resources/examples/embedded/riscv-qemu/semihost.c3

@@ -0,0 +1,20 @@
+module semihost;
+
+// See: https://github.com/ARM-software/abi-aa/blob/main/semihosting/semihosting.rst#sys-exit-extended-0x20
+
+extern fn int sys_semihost(int operation, SemihostParameters* parms);
+
+struct SemihostParameters {
+	int field1;
+	int field2;
+}
+
+const int SYS_EXIT_EXTENDED = 0x20;
+const int ADP_STOPPED_APPLICATIONEXIT = 0x20026;
+
+fn void exit(int status) {
+	SemihostParameters parms;
+	parms.field1 = ADP_STOPPED_APPLICATIONEXIT;
+	parms.field2 = status;
+	sys_semihost(SYS_EXIT_EXTENDED, &parms);
+}

resources/examples/embedded/riscv-qemu/start.s

@@ -0,0 +1,29 @@
+# Simple C runtime startup bootstrap
+# Two primary functions:
+# - Stack allocation and initializing stack pointer
+# - Jumping to main
+
+.section .text._start
+.global _start
+_start:
+  la sp, __stack_top      # Load the stack pointer
+  add s0, sp, zero        # Set the frame pointer
+  jal zero, main          # Run main entry point - no argc
+loop:	j loop              # Spin forever in case main returns
+
+# Support semi-hosting calls
+.option norvc
+.text
+.balign 16
+.global sys_semihost
+.type sys_semihost @function
+sys_semihost:             # https://github.com/riscv-non-isa/riscv-semihosting/blob/main/src/binary-interface.adoc
+  slli zero, zero, 0x1f
+  ebreak
+  srai zero, zero, 0x7
+  ret
+
+.section .data
+.space 1024*8             # allocate 8K of memory to serve as initial stack
+.align 16                 # Smallest stack allocation is 16 bytes, so align accordingly
+__stack_top:              # The stack grows downward according the Risc-V ABI

resources/examples/embedded/riscv-qemu/uart.c3

@@ -0,0 +1,28 @@
+module uart;
+
+const UARTFCR_FFENA = 0x01;                  // UART FIFO Control Register enable bit
+const UARTLSR_THRE = 0x20;                   // UART Line Status Register Transmit Hold Register Empty bit
+
+struct Uart {
+	char dr;                                   // UART Data Register
+	char filler1;
+	char fcr;                                  // FIFO Control Register
+	char filler2;
+	char filler3;
+	char lsr;                                  // Line Status Register
+}
+
+fn bool Uart.uart_ff_thr_empty(Uart* this) {
+	return (bool)($$volatile_load(&this.lsr) & UARTLSR_THRE);
+}
+
+fn void Uart.putc(Uart* this, char c) {
+  while (!this.uart_ff_thr_empty());         // Wait until the FIFO holding register is empty
+  $$volatile_store(&this.dr, c);             // Write character to transmit register
+}
+
+fn void Uart.puts(Uart* this, char *str) {
+  while (*str) {                             // Loop until value at string pointer is zero
+    this.putc(*str++);                       // Write the character and increment pointer
+  }
+}

src/compiler/linker.c

@@ -247,50 +247,54 @@ static const char *find_freebsd_crt(void)
 	return NULL;
 }
 
-static const char *find_linux_crt(void)
+static const char *find_arch_glob_path(const char *glob_path, int file_len)
 {
-	if (active_target.linuxpaths.crt) return active_target.linuxpaths.crt;
 #if PLATFORM_POSIX
 	glob_t globbuf;
-	if (!glob("/usr/lib/*/crt1.o", 0, NULL, &globbuf) && globbuf.gl_pathc)
+	if (!glob(glob_path, 0, NULL, &globbuf))
 	{
-		const char *path = globbuf.gl_pathv[0];
-		INFO_LOG("Found crt at %s", path);
-		size_t len = strlen(path);
-		assert(len > 6);
-		const char *res = str_copy(path, len - 6);
+		for (int i = 0; i < globbuf.gl_pathc; i++)
+		{
+			const char *path = globbuf.gl_pathv[i];
+			// Avoid qemu problems
+			if (platform_target.arch != ARCH_TYPE_RISCV64
+			    && platform_target.arch != ARCH_TYPE_RISCV32
+			    && strstr(path, "riscv")) continue;
+			size_t len = strlen(path);
+			assert(len > file_len);
+			const char *res = str_copy(path, len - file_len);
+			globfree(&globbuf);
+			return res;
+		}
 		globfree(&globbuf);
-		return res;
-	}
-	else
-	{
-		INFO_LOG("No crt in /usr/lib/*/");
 	}
 #endif
 	return NULL;
 }
+static const char *find_linux_crt(void)
+{
+	if (active_target.linuxpaths.crt) return active_target.linuxpaths.crt;
+	const char *path = find_arch_glob_path("/usr/lib/*/crt1.o", 6);
+	if (!path)
+	{
+		INFO_LOG("No crt in /usr/lib/*/");
+		return NULL;
+	}
+	INFO_LOG("Found crt at %s", path);
+	return path;
+}
 
 static const char *find_linux_crt_begin(void)
 {
 	if (active_target.linuxpaths.crtbegin) return active_target.linuxpaths.crtbegin;
-#if PLATFORM_POSIX
-	glob_t globbuf;
-	if (!glob("/usr/lib/gcc/*/*/crtbegin.o", 0, NULL, &globbuf) && globbuf.gl_pathc)
-	{
-		const char *path = globbuf.gl_pathv[0];
-		INFO_LOG("Found crtbegin at %s", path);
-		size_t len = strlen(path);
-		assert(len > 10);
-		const char *res = str_copy(path, len - 10);
-		globfree(&globbuf);
-		return res;
-	}
-	else
+	const char *path = find_arch_glob_path("/usr/lib/gcc/*/*/crtbegin.o", 10);
+	if (!path)
 	{
 		INFO_LOG("No crtbegin in /usr/lib/gcc/*/*/");
+		return NULL;
 	}
-#endif
-	return NULL;
+	INFO_LOG("Found crtbegin at %s", path);
+	return path;
 }
 
 static void linker_setup_linux(const char ***args_ref, Linker linker_type)