On 29 May 2015 at 16:19, Alex Bennée <alex.bennee@xxxxxxxxxx> wrote:
> These don't involve messing around with debug registers, just setting
> the breakpoint instruction in memory. GDB will not use this mechanism if
> it can't access the memory to write the breakpoint.
>
> All the kernel has to do is ensure the hypervisor traps the breakpoint
> exceptions and returns to userspace.
>
> Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
>
> --
> v2
> - handle debug exit with new hsr exception info
> - add verbosity to UNIMP message
> v3
> - sync with kvm_cpu_synchronize_state() before checking PC.
> - use internals.h defines
> - use env->pc
> - use proper format types
> ---
> target-arm/kvm.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 76 insertions(+), 12 deletions(-)
>
> diff --git a/target-arm/kvm.c b/target-arm/kvm.c
> index fdd9ba3..c3bad6f 100644
> --- a/target-arm/kvm.c
> +++ b/target-arm/kvm.c
> @@ -510,9 +510,60 @@ void kvm_arch_post_run(CPUState *cs, struct kvm_run *run)
> {
> }
>
> +/* See v8 ARM ARM D7.2.27 ESR_ELx, Exception Syndrome Register
> + *
> + * To minimise translating between kernel and user-space the kernel
> + * ABI just provides user-space with the full exception syndrome
> + * register value to be decoded in QEMU.
> + */
> +
> +static int kvm_handle_debug(CPUState *cs, struct kvm_run *run)
> +{
> + struct kvm_debug_exit_arch *arch_info = &run->debug.arch;
> + int hsr_ec = arch_info->hsr >> ARM_EL_EC_SHIFT;
> + ARMCPU *cpu = ARM_CPU(cs);
> + CPUARMState *env = &cpu->env;
> +
> + /* Ensure PC is synchronised */
> + kvm_cpu_synchronize_state(cs);
> +
> + switch (hsr_ec) {
> + case EC_AA64_BKPT:
> + if (kvm_find_sw_breakpoint(cs, env->pc)) {
> + return true;
> + }
> + break;
> + default:
> + error_report("%s: unhandled debug exit (%"PRIx32", %"PRIx64")\n",
> + __func__, arch_info->hsr, env->pc);
> + }
> +
> + /* If we don't handle this it could be it really is for the
> + guest to handle */
> + qemu_log_mask(LOG_UNIMP,
> + "%s: re-injecting exception not yet implemented"
> + " (0x%"PRIx32", %"PRIx64")\n",
> + __func__, hsr_ec, env->pc);
> +
> + return false;
> +}
> +
> int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
> {
> - return 0;
> + int ret = 0;
> +
> + switch (run->exit_reason) {
> + case KVM_EXIT_DEBUG:
> + if (kvm_handle_debug(cs, run)) {
> + ret = EXCP_DEBUG;
> + } /* otherwise return to guest */
> + break;
> + default:
> + qemu_log_mask(LOG_UNIMP, "%s: un-handled exit reason %d\n",
> + __func__, run->exit_reason);
> + break;
> + }
> + return ret;
> }
>
> bool kvm_arch_stop_on_emulation_error(CPUState *cs)
> @@ -537,14 +588,33 @@ int kvm_arch_on_sigbus(int code, void *addr)
>
> void kvm_arch_update_guest_debug(CPUState *cs, struct kvm_guest_debug *dbg)
> {
> - qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
> + if (kvm_sw_breakpoints_active(cs)) {
> + dbg->control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP;
> + }
> }
>
> -int kvm_arch_insert_sw_breakpoint(CPUState *cs,
> - struct kvm_sw_breakpoint *bp)
> +/* C6.6.29 BRK instruction */
> +int kvm_arch_insert_sw_breakpoint(CPUState *cs, struct kvm_sw_breakpoint *bp)
> {
> - qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
> - return -EINVAL;
> + static const uint32_t brk = 0xd4200000;
#define, please, since you're using it here and in the remove fn.
> +
> + if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 4, 0) ||
> + cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&brk, 4, 1)) {
> + return -EINVAL;
> + }
> + return 0;
> +}
Shouldn't we be testing the "does the kernel implement debug"
flag before we allow gdb to write in bp insns or mess with
dbg->control ?
-- PMM
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