[binutils-gdb] Fix casting in-memory values of primitive types to const reference

[binutils-gdb] Fix casting in-memory values of primitive types to const reference

[Hannes Domani]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d391f3721e20d160909a3afae7fee647ea5575a2

commit d391f3721e20d160909a3afae7fee647ea5575a2
Author: Hannes Domani <ssbssa@yahoo.de>
Date:   Wed Mar 20 18:23:40 2024 +0100

    Fix casting in-memory values of primitive types to const reference
    
    It's currently not possible to cast an in-memory value of a primitive
    type to const reference:
    ```
    (gdb) p Q.id
    $1 = 42
    (gdb) p (int&)Q.id
    $2 = (int &) @0x22fd0c: 42
    (gdb) p (const int&)Q.id
    Attempt to take address of value not located in memory.
    ```
    
    And if in a function call an argument needs the same kind of casting,
    it also doesn't work:
    ```
    (gdb) l f3
    39      int f3(const int &i)
    40      {
    41        return i;
    42      }
    (gdb) p f3(Q.id)
    Attempt to take address of value not located in memory.
    ```
    
    It's because when the constness of the type changes in a call to
    value_cast, a new not_lval value is allocated, which doesn't exist
    in the target memory.
    
    Fixed by ignoring const/volatile/restrict qualifications in
    value_cast when comparing cast type to original type, so the new
    value will point to the same location as the original value:
    ```
    (gdb) p (int&)i
    $2 = (int &) @0x39f72c: 1
    (gdb) p (const int&)i
    $3 = (const int &) @0x39f72c: 1
    (gdb) p f3(Q.id)
    $4 = 42
    ```
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=19423
    Approved-By: Tom Tromey <tom@tromey.com>

Diff:
---
 gdb/testsuite/gdb.cp/casts.exp      | 3 +++
 gdb/testsuite/gdb.cp/ref-params.cc  | 6 ++++++
 gdb/testsuite/gdb.cp/ref-params.exp | 1 +
 gdb/valops.c                        | 3 ++-
 4 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.cp/casts.exp b/gdb/testsuite/gdb.cp/casts.exp
index ca82ab084b9..9f7638c8aee 100644
--- a/gdb/testsuite/gdb.cp/casts.exp
+++ b/gdb/testsuite/gdb.cp/casts.exp
@@ -180,6 +180,9 @@ gdb_test "print (unsigned long long) (LeftRight *) (Right *) &gd == gd_value" \
 gdb_test "print (unsigned long long) (LeftRight *) (Right *) r_value == gd_value" \
     " = true"
 
+gdb_test "print (const int &) gd.left" \
+    " = \\(const int \\&\\) @$nonzero_hex: 23"
+
 gdb_test "print reinterpret_cast<LeftRight *>(l) == lr_l" " = true"
 gdb_test "print reinterpret_cast<LeftRight *>(r) == lr_r" " = true"
 gdb_test "print reinterpret_cast<Left *>(lr) == l_lr" " = true"
diff --git a/gdb/testsuite/gdb.cp/ref-params.cc b/gdb/testsuite/gdb.cp/ref-params.cc
index f038d71fe10..3ef28688607 100644
--- a/gdb/testsuite/gdb.cp/ref-params.cc
+++ b/gdb/testsuite/gdb.cp/ref-params.cc
@@ -36,6 +36,11 @@ int f2(Child& C)
   return f1(C);			/* Set breakpoint marker2 here.  */
 }
 
+int f3(const int &i)
+{
+  return i;
+}
+
 struct OtherParent {
   OtherParent (int other_id0) : other_id(other_id0) { }
   int other_id;
@@ -64,6 +69,7 @@ int main(void)
 
   f2(Q);
   f2(QR);
+  f3(Q.id);
 
   MultiChild MQ(53);
   MultiChild& MQR = MQ;
diff --git a/gdb/testsuite/gdb.cp/ref-params.exp b/gdb/testsuite/gdb.cp/ref-params.exp
index 03bb8e62496..e5c28e6e2ad 100644
--- a/gdb/testsuite/gdb.cp/ref-params.exp
+++ b/gdb/testsuite/gdb.cp/ref-params.exp
@@ -62,3 +62,4 @@ gdb_test "print mf2(MQ)" ".* = 106"
 gdb_test "print f1(MQR)" ".* = 53"
 gdb_test "print mf1(MQR)" ".* = 106"
 gdb_test "print mf2(MQR)" ".* = 106"
+gdb_test "print f3(Q.id)" ".* = 42"
diff --git a/gdb/valops.c b/gdb/valops.c
index 1a943f0fc78..52cce287281 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -411,7 +411,8 @@ value_cast (struct type *type, struct value *arg2)
      In this case we want to preserve the LVAL of ARG2 as this allows the
      resulting value to be used in more places.  We do this by calling
      VALUE_COPY if appropriate.  */
-  if (types_deeply_equal (arg2->type (), type))
+  if (types_deeply_equal (make_unqualified_type (arg2->type ()),
+			  make_unqualified_type (type)))
     {
       /* If the types are exactly equal then we can avoid creating a new
 	 value completely.  */