[PATCH v2 02/50] accel/tcg: Add getpc helper

Introduces a helper function to return the current pc (returnaddress of
the helper), this allows helper-to-tcg to correctly translate nested
helper functions that checks for faulting memory operations.

This is useful as an optimization where a helper functions has a
commonly taken fast path that doesn't fault e.g.

  void HELPER(outer)(...)
  {
      ... // non faulting operations
      if (some_uncommon_condition) {
          helper_inner(..., GETPC())
      }
  }

the outer helper along with the condition can then be emitted as TCG,
and helper_inner() will be emitted as a gen_helper_inner(, ra), where ra
is the result of gen_helper_getpc().

NOTE: This is not ideal since we're introducing extra helper calls,
      and the solution doesn't deal with the "inner" function not being
      a helper.  A better solution and what we'll probably do in the
      next version of the patchset is to instead emit a helper
      definition for the "inner" function that uses GETPC().

Signed-off-by: Anton Johansson <[email protected]>
---
 accel/tcg/tcg-runtime.c | 5 +++++
 accel/tcg/tcg-runtime.h | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/accel/tcg/tcg-runtime.c b/accel/tcg/tcg-runtime.c
index d42c00736b..87b9530a50 100644
--- a/accel/tcg/tcg-runtime.c
+++ b/accel/tcg/tcg-runtime.c
@@ -162,3 +162,8 @@ void HELPER(exit_atomic)(CPUArchState *env)
 {
     cpu_loop_exit_atomic(env_cpu(env), GETPC());
 }
+
+uint64_t HELPER(getpc)(void)
+{
+    return GETPC();
+}
diff --git a/accel/tcg/tcg-runtime.h b/accel/tcg/tcg-runtime.h
index 197d658b40..e25712d1fc 100644
--- a/accel/tcg/tcg-runtime.h
+++ b/accel/tcg/tcg-runtime.h
@@ -30,6 +30,8 @@ DEF_HELPER_FLAGS_1(lookup_tb_ptr, TCG_CALL_NO_WG_SE, cptr, env)
 
 DEF_HELPER_FLAGS_1(exit_atomic, TCG_CALL_NO_WG, noreturn, env)
 
+DEF_HELPER_FLAGS_0(getpc, TCG_CALL_NO_RWG_SE, i64)
+
 #ifndef IN_HELPER_PROTO
 /*
  * Pass calls to memset directly to libc, without a thunk in qemu.
-- 
2.52.0