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[PULL,6/9] target/arm: Suppress debug exceptions when OS Lock set

Message ID 20220707122734.288929-7-peter.maydell@linaro.org
State Accepted
Commit 40b200279c98ea0c223fa5a2bdeb4aee40d4e40e
Headers show
Series [PULL,1/9] hw/arm/virt: dt: add rng-seed property | expand

Commit Message

Peter Maydell July 7, 2022, 12:27 p.m. UTC 
The "OS Lock" in the Arm debug architecture is a way for software
to suppress debug exceptions while it is trying to power down
a CPU and save the state of the breakpoint and watchpoint
registers. In QEMU we implemented the support for writing
the OS Lock bit via OSLAR_EL1 and reading it via OSLSR_EL1,
but didn't implement the actual behaviour.

The required behaviour with the OS Lock set is:
 * debug exceptions (apart from BKPT insns) are suppressed
 * some MDSCR_EL1 bits allow write access to the corresponding
   EDSCR external debug status register that they shadow
   (we can ignore this because we don't implement external debug)
 * similarly with the OSECCR_EL1 which shadows the EDECCR
   (but we don't implement OSECCR_EL1 anyway)

Implement the missing behaviour of suppressing debug
exceptions.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220630194116.3438513-4-peter.maydell@linaro.org
---
 target/arm/debug_helper.c | 3 +++
 1 file changed, 3 insertions(+)
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Patch

diff --git a/target/arm/debug_helper.c b/target/arm/debug_helper.c
index 9a78c1db966..691b9b74c4a 100644
--- a/target/arm/debug_helper.c
+++ b/target/arm/debug_helper.c
@@ -142,6 +142,9 @@  static bool aa32_generate_debug_exceptions(CPUARMState *env)
  */
 bool arm_generate_debug_exceptions(CPUARMState *env)
 {
+    if (env->cp15.oslsr_el1 & 1) {
+        return false;
+    }
     if (is_a64(env)) {
         return aa64_generate_debug_exceptions(env);
     } else {