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Re: [PATCH 3/5] target/arm: Suppress debug exceptions when OS Lock set


From: Richard Henderson
Subject: Re: [PATCH 3/5] target/arm: Suppress debug exceptions when OS Lock set
Date: Sat, 2 Jul 2022 19:30:49 +0530
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1

On 7/1/22 01:11, Peter Maydell wrote:
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>
---
  target/arm/debug_helper.c | 3 +++
  1 file changed, 3 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~



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