Fix asm, can use pseudo ops.

Makefile

@@ -79,6 +79,7 @@ endif
 ld := $(prefix)ld
 objdump := $(prefix)objdump
 cc := $(prefix)gcc
+as := $(prefix)as
 
 .PHONY: all clean run iso build asm doc justrun kernel
 
@@ -137,6 +138,10 @@ build/arch/x86_64/boot/%.o: $(boot_src)/%.asm
 	@mkdir -p $(shell dirname $@)
 	@nasm -felf64 $< -o $@
 
+build/arch/riscv32/boot/%.o: $(boot_src)/%.asm
+	@mkdir -p $(shell dirname $@)
+	@$(as) -march=rv32i $< -o $@
+
 # make .o from .img file
 build/user/%.o: user/%.img
 	@mkdir -p $(shell dirname $@)

src/arch/riscv32/boot/entry.asm

@@ -1,13 +1,8 @@
     .section .text,"ax",%progbits
     .globl kern_entry
 kern_entry:
-    # la sp, bootstacktop
-    auipc sp, %hi(bootstacktop)
-    addi sp, sp, %lo(bootstacktop)
-
-    # tail rust_main
-    auipc t1, %hi(rust_main)
-    jalr zero, t1, %lo(rust_main)
+    la sp, bootstacktop
+    tail rust_main
 
 .section .data
     .align 12  #PGSHIFT

src/arch/riscv32/mod.rs

@@ -1,5 +1,3 @@
-global_asm!(include_str!("boot/entry.S"));
-
 extern crate riscv;
 extern crate bbl;