[Qemu-devel] [PATCH v2] target-arm: Fix resetting issues on ARMv7-M CPUs

[Martin Galvan]

When calling qemu_system_reset after startup on a Cortex-M CPU, the
initial values of PC, MSP and the Thumb bit weren't set correctly. In
particular, since Thumb was 0, a Usage Fault would arise immediately
after trying to excecute any instruction on a Cortex-M.

Signed-off-by: Martin Galvan <address@hidden>
---

Changed since previous version: We're not adding initial_MSP and
initial_PC to the CPU state. Instead, we're loading the initial values
using ldl_phys.

 target-arm/cpu.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/target-arm/cpu.c b/target-arm/cpu.c
index 5ac1bf9..9dfa50e 100644
--- a/target-arm/cpu.c
+++ b/target-arm/cpu.c
@@ -136,14 +136,22 @@ static void arm_cpu_reset(CPUState *s)
         env->daif &= ~PSTATE_I;
         rom = rom_ptr(0);
         if (rom) {
-            /* We should really use ldl_phys here, in case the guest
-               modified flash and reset itself.  However images
-               loaded via -kernel have not been copied yet, so load the
-               values directly from there.  */
+            /* Address zero is covered by ROM which hasn't yet been
+               copied into physical memory. */
             env->regs[13] = ldl_p(rom) & 0xFFFFFFFC;
             pc = ldl_p(rom + 4);
             env->thumb = pc & 1;
             env->regs[15] = pc & ~1;
+        } else {
+            /* Address zero not covered by a ROM blob, or the ROM blob
+               is in non-modifiable memory and this is a second reset after
+               it got copied into memory. In the latter case, rom_ptr
will return
+               a NULL pointer and we should use ldl_phys instead.
+            */
+            env->regs[13] = ldl_phys(s->as, 0) & 0xFFFFFFFC;
+            pc = ldl_phys(s->as, 4);
+            env->thumb = pc & 1;
+            env->regs[15] = pc & ~1;
         }
     }

-- 
1.9.1

-- 


Martín Galván

Software Engineer

Taller Technologies Argentina

San Lorenzo 47, 3rd Floor, Office 5

Córdoba, Argentina

Phone: 54 351 4217888 / +54 351 4218211