[PATCH v2 1/3] target/riscv/kvm: add software breakpoints support

[Chao Du <duchao@eswincomputing.com>]

This patch implements insert/remove software breakpoint process.

For RISC-V, GDB treats single-step similarly to breakpoint: add a
breakpoint at the next step address, then continue. So this also
works for single-step debugging.

Implement kvm_arch_update_guest_debug(): Set the control flag
when there are active breakpoints. This will help KVM to know
the status in the userspace.

Add some stubs which are necessary for building, and will be
implemented later.

Signed-off-by: Chao Du <duchao@eswincomputing.com>
---
 target/riscv/kvm/kvm-cpu.c | 69 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index 235e2cdaca..c50f058aff 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -1969,3 +1969,72 @@ static const TypeInfo riscv_kvm_cpu_type_infos[] = {
 };
 
 DEFINE_TYPES(riscv_kvm_cpu_type_infos)
+
+static const uint32_t ebreak_insn = 0x00100073;
+static const uint16_t c_ebreak_insn = 0x9002;
+
+int kvm_arch_insert_sw_breakpoint(CPUState *cs, struct kvm_sw_breakpoint *bp)
+{
+    if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 2, 0)) {
+        return -EINVAL;
+    }
+
+    if ((bp->saved_insn & 0x3) == 0x3) {
+        if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 4, 0)
+            || cpu_memory_rw_debug(cs, bp->pc, &ebreak_insn, 4, 1)) {
+            return -EINVAL;
+        }
+    } else {
+        if (cpu_memory_rw_debug(cs, bp->pc, &c_ebreak_insn, 2, 1)) {
+            return -EINVAL;
+        }
+    }
+
+    return 0;
+}
+
+int kvm_arch_remove_sw_breakpoint(CPUState *cs, struct kvm_sw_breakpoint *bp)
+{
+    uint32_t ebreak;
+    uint16_t c_ebreak;
+
+    if ((bp->saved_insn & 0x3) == 0x3) {
+        if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&ebreak, 4, 0) ||
+            ebreak != ebreak_insn ||
+            cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 4, 1)) {
+            return -EINVAL;
+        }
+    } else {
+        if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&c_ebreak, 2, 0) ||
+            c_ebreak != c_ebreak_insn ||
+            cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 2, 1)) {
+            return -EINVAL;
+        }
+    }
+
+    return 0;
+}
+
+int kvm_arch_insert_hw_breakpoint(vaddr addr, vaddr len, int type)
+{
+    /* TODO; To be implemented later. */
+    return -EINVAL;
+}
+
+int kvm_arch_remove_hw_breakpoint(vaddr addr, vaddr len, int type)
+{
+    /* TODO; To be implemented later. */
+    return -EINVAL;
+}
+
+void kvm_arch_remove_all_hw_breakpoints(void)
+{
+    /* TODO; To be implemented later. */
+}
+
+void kvm_arch_update_guest_debug(CPUState *cs, struct kvm_guest_debug *dbg)
+{
+    if (kvm_sw_breakpoints_active(cs)) {
+        dbg->control |= KVM_GUESTDBG_ENABLE;
+    }
+}
-- 
2.17.1