[binutils-gdb] gdb: constify parameter of value_copy

[Simon Marchi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=5f8ab46bc6918efb678deb5956c033e466afe301

commit 5f8ab46bc6918efb678deb5956c033e466afe301
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Mon Jan 31 15:57:58 2022 -0500

    gdb: constify parameter of value_copy
    
    In a following patch, I have a const value I want to copy using a
    value_copy.  However, value_copy takes a non-const source value, at the
    moment.  Change the paramter to be const,
    
    If the source value is not lazy, we currently call
    value_contents_all_raw, which calls allocate_value_contents, to get a
    view on the contents.  They both take a non-const value, that's a
    problem.  My first attempt at solving it was to add a const version of
    value_contents_all_raw, make allocate_value_contents take a const value,
    and either:
    
     - make value::contents mutable
     - make allocate_value_contents cast away the const
    
    The idea being that allocating the value contents buffer does modify the
    value at the bit level, but logically that doesn't change its state.
    
    That was getting a bit complicated, so what I ended up doing is make
    value_copy not call value_contents_all_raw.  We know at this point that
    the value is not lazy, so value::contents must have been allocate
    already.
    
    Change-Id: I3741ab362bce14315f712ec24064ccc17e3578d4

Diff:
---
 gdb/value.c | 13 +++++++++----
 gdb/value.h |  2 +-
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/gdb/value.c b/gdb/value.c
index 080af487c56..a57a83207e2 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1703,7 +1703,7 @@ value_release_to_mark (const struct value *mark)
    but it's a different block of storage.  */
 
 struct value *
-value_copy (struct value *arg)
+value_copy (const value *arg)
 {
   struct type *encl_type = value_enclosing_type (arg);
   struct value *val;
@@ -1713,7 +1713,7 @@ value_copy (struct value *arg)
   else
     val = allocate_value (encl_type);
   val->type = arg->type;
-  VALUE_LVAL (val) = VALUE_LVAL (arg);
+  VALUE_LVAL (val) = arg->lval;
   val->location = arg->location;
   val->offset = arg->offset;
   val->bitpos = arg->bitpos;
@@ -1727,8 +1727,13 @@ value_copy (struct value *arg)
   val->initialized = arg->initialized;
 
   if (!value_lazy (val))
-    copy (value_contents_all_raw (arg),
-	  value_contents_all_raw (val));
+    {
+      gdb_assert (arg->contents != nullptr);
+      ULONGEST length = TYPE_LENGTH (value_enclosing_type (arg));
+      const auto &arg_view
+	= gdb::make_array_view (arg->contents.get (), length);
+      copy (arg_view, value_contents_all_raw (val));
+    }
 
   val->unavailable = arg->unavailable;
   val->optimized_out = arg->optimized_out;
diff --git a/gdb/value.h b/gdb/value.h
index f7b29022d37..4cd2044ac7c 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -1127,7 +1127,7 @@ extern void preserve_values (struct objfile *);
 
 /* From values.c */
 
-extern struct value *value_copy (struct value *);
+extern struct value *value_copy (const value *);
 
 extern struct value *value_non_lval (struct value *);