Fix runcmd issue with gcc + configure PMP correctly

Makefile

@@ -174,6 +174,9 @@ QEMUOPTS = -machine virt -bios none -kernel $K/kernel -m 128M -smp $(CPUS) -nogr
 QEMUOPTS += -drive file=fs.img,if=none,format=raw,id=x0 -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0
 QEMUOPTS += -monitor telnet:127.0.0.1:12345,server,nowait
 
+qemu-version:
+	$(QEMU) --version
+
 qemu: $K/kernel fs.img
 	$(QEMU) $(QEMUOPTS)
 

kernel/riscv.h

@@ -183,6 +183,18 @@ w_mtvec(uint64 x)
   asm volatile("csrw mtvec, %0" : : "r" (x));
 }
 
+static inline void
+w_pmpcfg0(uint64 x)
+{
+  asm volatile("csrw pmpcfg0, %0" : : "r" (x));
+}
+
+static inline void
+w_pmpaddr0(uint64 x)
+{
+  asm volatile("csrw pmpaddr0, %0" : : "r" (x));
+}
+
 // use riscv's sv39 page table scheme.
 #define SATP_SV39 (8L << 60)
 

kernel/start.c

@@ -38,6 +38,11 @@ start()
   w_mideleg(0xffff);
   w_sie(r_sie() | SIE_SEIE | SIE_STIE | SIE_SSIE);
 
+  // configure Physical Memory Protection to give supervisor mode
+  // access to all of physical memory.
+  w_pmpaddr0(0x3fffffffffffffull);
+  w_pmpcfg0(0xf);
+
   // ask for clock interrupts.
   timerinit();
 

user/sh.c

@@ -54,6 +54,7 @@ void panic(char*);
 struct cmd *parsecmd(char*);
 
 // Execute cmd.  Never returns.
+__attribute__((noreturn))
 void
 runcmd(struct cmd *cmd)
 {