[binutils-gdb] gdb: add comment in dwarf_evaluate_loc_desc::push_dwarf_reg_entry_value

[Simon Marchi <simark@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=989ade05525047fc6b94f24ece5fc09e076027b0

commit 989ade05525047fc6b94f24ece5fc09e076027b0
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Thu May 28 15:47:53 2020 -0400

    gdb: add comment in dwarf_evaluate_loc_desc::push_dwarf_reg_entry_value
    
    Add a comment to clarify why we temporarily override some of the
    context's fields, and especially the per_objfile field.  A longer
    explanation can be found in this previous commit
    
        44486dcf19b ("gdb: use caller objfile in dwarf_evaluate_loc_desc::push_dwarf_reg_entry_value")
    
    gdb/ChangeLog:
    
            * dwarf2/loc.c (class dwarf_evaluate_loc_desc)
            <push_dwarf_reg_entry_value>: Add comment.
    
    Change-Id: I60c6e1062799f729b30a9db78bcb6448783324b4

Diff:
---
 gdb/ChangeLog    | 5 +++++
 gdb/dwarf2/loc.c | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index cf46c4e92bd..44300d258ea 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-28  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* dwarf2/loc.c (class dwarf_evaluate_loc_desc)
+	<push_dwarf_reg_entry_value>: Add comment.
+
 2020-05-28  Kevin Buettner  <kevinb@redhat.com>
 	    Keith Seitz  <keiths@redhat.com>
 
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index 1aab1a4f51b..400bb4d16fc 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -731,6 +731,12 @@ public:
       throw_error (NO_ENTRY_VALUE_ERROR,
 		   _("Cannot resolve DW_AT_call_data_value"));
 
+    /* We are about to evaluate an expression in the context of the caller
+       of the current frame.  This evaluation context may be different from
+       the current (callee's) context), so temporarily set the caller's context.
+
+       It is possible for the caller to be from a different objfile from the
+       callee if the call is made through a function pointer.  */
     scoped_restore save_frame = make_scoped_restore (&this->frame,
 						     caller_frame);
     scoped_restore save_per_cu = make_scoped_restore (&this->per_cu,