When calling qemu_system_reset after startup on a Cortex-M
CPU, the initial values of PC, MSP and the Thumb bit weren't being set
correctly if the vector table was in ROM. In particular, since Thumb was 0, a
Usage Fault would arise immediately after trying to execute any instruction
on a Cortex-M.
Signed-off-by: Martin Galvan <martin.gal...@tallertechnologies.com>
---
Changed in v3: Fixed a few style issues.
Changed in v2: 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 | 34 +++++++++++++++++++++++-------
----
1 file changed, 23 insertions(+), 11 deletions(-)
diff --git a/target-arm/cpu.c b/target-arm/cpu.c
index 8199f32..8e9f203 100644
--- a/target-arm/cpu.c
+++ b/target-arm/cpu.c
@@ -129,26 +129,38 @@ static void arm_cpu_reset(CPUState *s)
env->uncached_cpsr = ARM_CPU_MODE_SVC;
env->daif = PSTATE_D | PSTATE_A | PSTATE_I | PSTATE_F;
/* On ARMv7-M the CPSR_I is the value of the PRIMASK register, and is
- clear at reset. Initial SP and PC are loaded from ROM. */
+ * clear at reset. Initial SP and PC are loaded from ROM.
+ */
if (IS_M(env)) {
- uint32_t pc;
+ uint32_t initial_msp; /* Loaded from 0x0 */
+ uint32_t initial_pc; /* Loaded from 0x4 */
uint8_t *rom;
+
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. */
- env->regs[13] = ldl_p(rom) & 0xFFFFFFFC;
- pc = ldl_p(rom + 4);
- env->thumb = pc & 1;
- env->regs[15] = pc & ~1;
+ /* Address zero is covered by ROM which hasn't yet been
+ * copied into physical memory.
+ */
+ initial_msp = ldl_p(rom);
+ initial_pc = ldl_p(rom + 4);
+ } 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.
+ */
+ initial_msp = ldl_phys(s->as, 0);
+ initial_pc = ldl_phys(s->as, 4);
}
+
+ env->regs[13] = initial_msp & 0xFFFFFFFC;
+ env->regs[15] = initial_pc & ~1;
+ env->thumb = initial_pc & 1; /* Must always be 1 for ARMv7-M */
}
if (env->cp15.c1_sys & SCTLR_V) {
- env->regs[15] = 0xFFFF0000;
+ env->regs[15] = 0xFFFF0000;
}
env->vfp.xregs[ARM_VFP_FPEXC] = 0;
--
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
