arm32: unwind: print_stack(): fix unwind_state

print_stack() must save r7 and r11 in the unwind_state structure. Not
doing so will likely result in a crash dunring unwind.
Register r7 is typically used as a frame pointer by GCC in Thumb2 mode,
while r11 (a.k.a. fp) is the frame pointer in ARM mode.

Also, set PC to the beginning of print_stack() since there's no point
in going further inside the function.

Fixes: OP-TEE/optee_os#1069
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (HiKey)
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (QEMU)
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>

core/arch/arm/include/arm32.h

@@ -558,6 +558,22 @@ static __always_inline uint32_t read_lr(void)
 	asm volatile ("mov %0, lr" : "=r" (val));
 	return val;
 }
+
+static __always_inline uint32_t read_fp(void)
+{
+	uint32_t val;
+
+	asm volatile ("mov %0, fp" : "=r" (val));
+	return val;
+}
+
+static __always_inline uint32_t read_r7(void)
+{
+	uint32_t val;
+
+	asm volatile ("mov %0, r7" : "=r" (val));
+	return val;
+}
 #endif /*ASM*/
 
 #endif /*ARM32_H*/

core/arch/arm/kernel/unwind_arm32.c

@@ -367,10 +367,14 @@ void print_stack(int level)
 {
 	struct unwind_state state;
 
-	memset(&state, 0, sizeof(state));
+	memset(state.registers, 0, sizeof(state.registers));
+	/* r7: Thumb-style frame pointer */
+	state.registers[7] = read_r7();
+	/* r11: ARM-style frame pointer */
+	state.registers[FP] = read_fp();
 	state.registers[SP] = read_sp();
 	state.registers[LR] = read_lr();
-	state.registers[PC] = read_pc();
+	state.registers[PC] = (uint32_t)print_stack;
 
 	do {
 		switch (level) {