Before handling updiscon (uninferable PC discontinuity) cases add the
encoded message we're going to use, format 2. Format 1 will be added
when we add the branch map.

There are design decisions worth documenting in this patch. For irreport,
the e-trace-encap spec [1] in section 7.6. "Format 2 packets",  says that
we should make this bit !updiscon if we're either:

"following a return because its address differs from the predicted return
address at the top of the implicit_return return address stack, or the
last retired before an exception, interrupt, privilege change or resync
because it is necessary to report the current address stack depth or
nested call count."

We do not implement any form of call/return prediction in the encoder,
and TCG will always retire a single insn per cycle. This means that
we'll never set irreport, i.e. irreport will always be equal to
updiscon. If this interpretation turns out to be wrong we'll revisit
this helper.

Likewise, irdepth is also not implemented since we'll always return a
package where irreport == updiscon. The size of the field is arbitrarily
set to '3' to avoid adding padding in the end of the msg to complete an
extra byte.

[1] https://github.com/riscv-non-isa/e-trace-encap/releases/tag/v1.0

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 hw/riscv/rv-trace-messages.c | 59 ++++++++++++++++++++++++++++++++++++
 hw/riscv/rv-trace-messages.h |  2 ++
 2 files changed, 61 insertions(+)

diff --git a/hw/riscv/rv-trace-messages.c b/hw/riscv/rv-trace-messages.c
index 3e9466633d..3fa70ba81c 100644
--- a/hw/riscv/rv-trace-messages.c
+++ b/hw/riscv/rv-trace-messages.c
@@ -53,6 +53,17 @@ typedef struct RVTraceTrapPayload {
 } RVTraceTrapPayload;
 #define TRAP_PAYLOAD_SIZE_64BITS 18
 
+typedef struct RVTraceFormat2Payload {
+    uint8_t format:2;
+    uint32_t addressLow;
+    uint32_t addressHigh;
+    uint8_t notify:1;
+    uint8_t updiscon:1;
+    uint8_t irreport:1;
+    uint8_t irdepth:3;
+} RVTraceFormat2Payload;
+#define FORMAT2_PAYLOAD_SIZE_64BITS 9
+
 static void rv_etrace_write_bits(uint8_t *bytes, uint32_t bit_pos,
                                  uint32_t num_bits, uint32_t val)
 {
@@ -186,3 +197,51 @@ size_t rv_etrace_gen_encoded_trap_msg(uint8_t *buf, uint64_t trap_addr,
 out:
     return HEADER_SIZE + header.length;
 }
+
+/*
+ * Note: irreport and irdepth is always == updiscon.
+ *
+ * return_stack_size_p + call_counter_size_p is hardcoded
+ * to 3 since we don't implement neither ATM.
+ */
+size_t rv_etrace_gen_encoded_format2_msg(uint8_t *buf, uint64_t addr,
+                                         bool notify, bool updiscon)
+{
+    RVTraceFormat2Payload payload = {.format = 0b11,
+                                     .notify = notify,
+                                     .updiscon = updiscon};
+    RVTraceMessageHeader header = {.flow = 0, .extend = 0,
+                                   .length = FORMAT2_PAYLOAD_SIZE_64BITS};
+    uint8_t bit_pos;
+
+    payload.addressLow = extract64(addr, 0, 32);
+    payload.addressHigh = extract64(addr, 32, 32);
+
+    payload.irreport = updiscon;
+    if (updiscon) {
+        payload.irdepth = 0b111;
+    } else {
+        payload.irdepth = 0;
+    }
+
+    rv_etrace_write_header(buf, header);
+    bit_pos = 8;
+
+    rv_etrace_write_bits(buf, bit_pos, 2, payload.format);
+    bit_pos += 2;
+
+    rv_etrace_write_bits(buf, bit_pos, 32, payload.addressLow);
+    bit_pos += 32;
+    rv_etrace_write_bits(buf, bit_pos, 32, payload.addressHigh);
+    bit_pos += 32;
+
+    rv_etrace_write_bits(buf, bit_pos, 1, payload.notify);
+    bit_pos += 1;
+    rv_etrace_write_bits(buf, bit_pos, 1, payload.updiscon);
+    bit_pos += 1;
+    rv_etrace_write_bits(buf, bit_pos, 1, payload.irreport);
+    bit_pos += 1;
+    rv_etrace_write_bits(buf, bit_pos, 3, payload.irdepth);
+
+    return HEADER_SIZE + header.length;
+}
diff --git a/hw/riscv/rv-trace-messages.h b/hw/riscv/rv-trace-messages.h
index f3e38b571f..50a4a0ef19 100644
--- a/hw/riscv/rv-trace-messages.h
+++ b/hw/riscv/rv-trace-messages.h
@@ -26,5 +26,7 @@ size_t rv_etrace_gen_encoded_trap_msg(uint8_t *buf, uint64_t trap_addr,
                                       uint8_t ecause,
                                       bool is_interrupt,
                                       uint64_t tval);
+size_t rv_etrace_gen_encoded_format2_msg(uint8_t *buf, uint64_t addr,
+                                         bool notify, bool updiscon);
 
 #endif
-- 
2.51.1