[PATCH 5/5] libdwfl: add interface for evaluating DWARF expressions in a frame

[Omar Sandoval]

From: Omar Sandoval <osan...@fb.com>

libdwfl can evaluate DWARF expressions in order to unwind the stack, but
this functionality isn't exposed to clients of the library. Now that the
pieces are in place, add dwfl_frame_eval_expr to provide this feature.

Signed-off-by: Omar Sandoval <osan...@fb.com>
---
 libdw/ChangeLog        |  1 +
 libdw/libdw.map        |  1 +
 libdwfl/ChangeLog      |  2 ++
 libdwfl/frame_unwind.c | 12 ++++++++++++
 libdwfl/libdwfl.h      |  6 ++++++
 5 files changed, 22 insertions(+)

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 1a712497..765d51ec 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -5,6 +5,7 @@
        Add dwfl_detach_thread.
        Add dwfl_frame_module.
        Add dwfl_frame_dwarf_frame.
+       Add dwfl_frame_eval_expr.
 
 2019-07-05  Omar Sandoval  <osan...@fb.com>
 
diff --git a/libdw/libdw.map b/libdw/libdw.map
index c1469c4e..d06a29ed 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -376,4 +376,5 @@ ELFUTILS_0.178 {
     dwfl_detach_thread;
     dwfl_frame_module;
     dwfl_frame_dwarf_frame;
+    dwfl_frame_eval_expr;
 } ELFUTILS_0.177;
diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index fdb517c9..3689ddd9 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -20,10 +20,12 @@
        (__libdwfl_frame_unwind): Cache state->mod.
        (dwfl_frame_module): Add function.
        (dwfl_frame_dwarf_frame): Add function.
+       (dwfl_frame_eval_expr): Add function.
        * libdwfl.h (dwfl_attach_thread): Add definition.
        (dwfl_detach_thread): Add definition.
        (dwfl_frame_module): Add definition.
        (dwfl_frame_dwarf_frame): Add definition.
+       (dwfl_frame_eval_expr): Add definition.
        * libdwflP.h (struct Dwfl_Thread): Update comment for unwound member.
        Add mod, frame, and bias.
 
diff --git a/libdwfl/frame_unwind.c b/libdwfl/frame_unwind.c
index 9738ca72..4c2df837 100644
--- a/libdwfl/frame_unwind.c
+++ b/libdwfl/frame_unwind.c
@@ -787,3 +787,15 @@ dwfl_frame_dwarf_frame (Dwfl_Frame *state, Dwarf_Addr 
*bias)
   *bias = state->bias;
   return state->frame;
 }
+
+bool
+dwfl_frame_eval_expr (Dwfl_Frame *state, const Dwarf_Op *ops, size_t nops,
+                     Dwarf_Addr *result)
+{
+  if (state->frame == NULL)
+    {
+      __libdwfl_seterrno (DWFL_E_NO_DWARF);
+      return false;
+    }
+  return expr_eval (state, state->frame, ops, nops, result, state->bias);
+}
diff --git a/libdwfl/libdwfl.h b/libdwfl/libdwfl.h
index b450816b..90a3e103 100644
--- a/libdwfl/libdwfl.h
+++ b/libdwfl/libdwfl.h
@@ -829,6 +829,12 @@ int dwfl_getthread_frames (Dwfl *dwfl, pid_t tid,
 bool dwfl_frame_pc (Dwfl_Frame *state, Dwarf_Addr *pc, bool *isactivation)
   __nonnull_attribute__ (1, 2);
 
+/* Evaluate a DWARF expression in the context of a frame.  On success, returns
+   true and fills in *RESULT.  On error, returns false. */
+bool dwfl_frame_eval_expr (Dwfl_Frame *state, const Dwarf_Op *ops, size_t nops,
+                          Dwarf_Addr *result)
+  __nonnull_attribute__ (1, 2, 4);
+
 #ifdef __cplusplus
 }
 #endif
-- 
2.23.0