os-workshop

commit 2f3b11ec75c68279c91046161facfda8bc5ef638
parent 7d0ab3714f20e5cab1081cec8645f77c17f75a44
Author: Brian Swetland <swetland@frotz.net>
Date:   Sat, 23 Apr 2022 18:19:34 -0700

start: don't clobber device tree, don't be main

- qemu arranges for the device tree to be in a1
- pass that on to start and throw the sp in a0
- main() usually expects argc/argv

Diffstat:
M
hw/src/start.S
 | 
5
++---
M
misc/info.c
 | 
3
++-
M
misc/mandelbrot.c
 | 
3
+--

3 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/hw/src/start.S b/hw/src/start.S
@@ -4,9 +4,8 @@
 .globl _start
 _start:
 	li sp, 0x81000000
-	li a0, 0
-	li a1, 0
-	jal main
+	mv a0, sp
+	jal start
 
 .globl exit
 exit:
diff --git a/misc/info.c b/misc/info.c
@@ -4,11 +4,12 @@
 #include <hw/debug.h>
 #include <hw/riscv.h>
 
-void main(void) {
+void start(uint32_t sp, uint32_t dtb) {
 	xprintf("Hello?\n");
 	xprintf("MSTATUS    %08x\n", csr_read(CSR_MSTATUS));
 	xprintf("MISA       %08x\n", csr_read(CSR_MISA));
 	xprintf("MCYCLE     %08x\n", csr_read(CSR_MCYCLE));
+	xprintf("DeviceTree %08x\n", dtb);
 
 	uint32_t n = csr_read(CSR_MISA);
 	xprintf("ISA: RV32");
diff --git a/misc/mandelbrot.c b/misc/mandelbrot.c
@@ -3,7 +3,7 @@
 
 #include <hw/debug.h>
 
-int main(int argc, char** argv) {
+void start(void) {
 	int top = 1000, bottom = -1000, ystep = 50;
 	int left = -2500, right = 1000, xstep = 30;
 	int maxiter = 1000;
@@ -28,5 +28,4 @@ int main(int argc, char** argv) {
 	}
 
 	xprintf("Hello, Mandlebrot!\n");
-	return 0;
 }