The wfi instruction can be configured to be trapped by a higher exception level, such as the EL2 hypervisor. When the instruction is trapped, the program counter should contain the address of the wfi instruction that caused the exception. The program counter is adjusted for this in the wfi op helper function. However, this correction is done to env->pc, which only applies to AArch64 mode. For AArch32, the program counter is stored in env->regs[15]. This adds an if-else statement to modify the correct program counter location based on the the current CPU mode. Signed-off-by: Jeff Kubascik <jeff.kubascik@dornerworks.com> --- Hello, I am using the ARMv8 version of QEMU to run the Xen hypervisor with a guest virtual machine compiled for AArch32/Thumb code. I have noticed that when the AArch32 guest VM executes the wfi instruction, the hypervisor trap of the wfi instruction sees the program counter contain the address of the instruction following the wfi. This does not occur for an AARch64 guest VM; in this case, the program counter contains the address of the wfi instruction. I am confident the correct behavior in both cases is for the program counter to contain the address of the wfi instruction, as this works on actual hardware (Xilinx Zynq UltraScale+ MPSoC). I have tested the above patch and it works for Xen with both an AArch64 guest (Linux) and an AArch32 guest (RTEMS). I'm still getting accustomed to the QEMU code base, so it may not be correct. Any feedback would be greatly appreciated. Sincerely, Jeff Kubascik --- target/arm/op_helper.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/target/arm/op_helper.c b/target/arm/op_helper.c index e5a346cb87..7295645854 100644 --- a/target/arm/op_helper.c +++ b/target/arm/op_helper.c @@ -295,7 +295,11 @@ void HELPER(wfi)(CPUARMState *env, uint32_t insn_len) } if (target_el) { - env->pc -= insn_len; + if (env->aarch64) + env->pc -= insn_len; + else + env->regs[15] -= insn_len; + raise_exception(env, EXCP_UDEF, syn_wfx(1, 0xe, 0, insn_len == 2), target_el); } -- 2.17.1
Patchew URL: https://patchew.org/QEMU/20200110180211.29025-1-jeff.kubascik@dornerworks.com/ Hi, This series seems to have some coding style problems. See output below for more information: Subject: [PATCH] target/arm: adjust program counter for wfi exception in AArch32 Type: series Message-id: 20200110180211.29025-1-jeff.kubascik@dornerworks.com === TEST SCRIPT BEGIN === #!/bin/bash git rev-parse base > /dev/null || exit 0 git config --local diff.renamelimit 0 git config --local diff.renames True git config --local diff.algorithm histogram ./scripts/checkpatch.pl --mailback base.. === TEST SCRIPT END === Switched to a new branch 'test' 800339c target/arm: adjust program counter for wfi exception in AArch32 === OUTPUT BEGIN === ERROR: braces {} are necessary for all arms of this statement #30: FILE: target/arm/op_helper.c:298: + if (env->aarch64) [...] + else [...] total: 1 errors, 0 warnings, 12 lines checked Commit 800339c7aaeb (target/arm: adjust program counter for wfi exception in AArch32) has style problems, please review. If any of these errors are false positives report them to the maintainer, see CHECKPATCH in MAINTAINERS. === OUTPUT END === Test command exited with code: 1 The full log is available at http://patchew.org/logs/20200110180211.29025-1-jeff.kubascik@dornerworks.com/testing.checkpatch/?type=message. --- Email generated automatically by Patchew [https://patchew.org/]. Please send your feedback to patchew-devel@redhat.com
On 1/10/20 8:02 AM, Jeff Kubascik wrote:
> - env->pc -= insn_len;
> + if (env->aarch64)
> + env->pc -= insn_len;
> + else
> + env->regs[15] -= insn_len;
QEMU requires all braces. See CODING_STYLE.
Otherwise,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
r~
On 1/13/2020 9:41 PM, Richard Henderson wrote: > On 1/10/20 8:02 AM, Jeff Kubascik wrote: >> - env->pc -= insn_len; >> + if (env->aarch64) >> + env->pc -= insn_len; >> + else >> + env->regs[15] -= insn_len; > > QEMU requires all braces. See CODING_STYLE. I received an automated email from Patchew regarding the coding style issue. I have submitted a v2 of the patch with this correction yesterday. > Otherwise, > Reviewed-by: Richard Henderson <richard.henderson@linaro.org> > > > r~ > Thanks! Jeff Kubascik