bbl: boot payload in machine mode when --enable-boot-machine is passed

bbl/bbl.c

@@ -58,7 +58,11 @@ void boot_other_hart(uintptr_t unused __attribute__((unused)))
     }
   }
 
+#ifdef BBL_BOOT_MACHINE
+  enter_machine_mode(entry, hartid, dtb_output());
+#else /* Run bbl in supervisor mode */
   enter_supervisor_mode(entry, hartid, dtb_output());
+#endif
 }
 
 void boot_loader(uintptr_t dtb)

machine/mentry.S

@@ -2,6 +2,7 @@
 
 #include "mtrap.h"
 #include "bits.h"
+#include "config.h"
 
   .data
   .align 6
@@ -18,7 +19,11 @@ trap_table:
   .word bad_trap
   .word mcall_trap
   .word bad_trap
+#ifdef BBL_BOOT_MACHINE
+  .word mcall_trap
+#else
   .word bad_trap
+#endif /* BBL_BOOT_MACHINE */
   .word bad_trap
 #define TRAP_FROM_MACHINE_MODE_VECTOR 13
   .word __trap_from_machine_mode

machine/minit.c

@@ -95,7 +95,9 @@ static void hart_init()
 {
   mstatus_init();
   fp_init();
+#ifndef BBL_BOOT_MACHINE
   delegate_traps();
+#endif /* BBL_BOOT_MACHINE */
 }
 
 static void plic_init()
@@ -213,3 +215,27 @@ void enter_supervisor_mode(void (*fn)(uintptr_t), uintptr_t arg0, uintptr_t arg1
   asm volatile ("mret" : : "r" (a0), "r" (a1));
   __builtin_unreachable();
 }
+
+void enter_machine_mode(void (*fn)(uintptr_t, uintptr_t), uintptr_t arg0, uintptr_t arg1)
+{
+  // Set up a PMP to permit access to all of memory.
+  // Ignore the illegal-instruction trap if PMPs aren't supported.
+  uintptr_t pmpc = PMP_NAPOT | PMP_R | PMP_W | PMP_X;
+  asm volatile ("la t0, 1f\n\t"
+                "csrrw t0, mtvec, t0\n\t"
+                "csrw pmpaddr0, %1\n\t"
+                "csrw pmpcfg0, %0\n\t"
+                ".align 2\n\t"
+                "1: csrw mtvec, t0"
+                : : "r" (pmpc), "r" (-1UL) : "t0");
+
+  uintptr_t mstatus = read_csr(mstatus);
+  mstatus = INSERT_FIELD(mstatus, MSTATUS_MPIE, 0);
+  write_csr(mstatus, mstatus);
+  write_csr(mscratch, MACHINE_STACK_TOP() - MENTRY_FRAME_SIZE);
+
+  /* Jump to the payload's entry point */
+  fn(arg0, arg1);
+
+  __builtin_unreachable();
+}

machine/mtrap.h

@@ -67,6 +67,8 @@ void putstring(const char* s);
 
 void enter_supervisor_mode(void (*fn)(uintptr_t), uintptr_t arg0, uintptr_t arg1)
   __attribute__((noreturn));
+void enter_machine_mode(void (*fn)(uintptr_t, uintptr_t), uintptr_t arg0, uintptr_t arg1)
+  __attribute__((noreturn));
 void boot_loader(uintptr_t dtb);
 void boot_other_hart(uintptr_t dtb);