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Fix reinterpret_cast for classes with multiple inheritance

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Currently a reinterpret_cast may change the pointer value if
multiple inheritance is involved:
```
(gdb) p r
$1 = (Right *) 0x22f75c
(gdb) p reinterpret_cast<LeftRight*>(r)
$2 = (LeftRight *) 0x22f758
```

It's because value_cast is called in this case, which automatically
does up- and downcasting.

Fixed by simply using the target pointer type in a copy of the
original value:
```
(gdb) p r
$1 = (Right *) 0x3bf87c
(gdb) p reinterpret_cast<LeftRight*>(r)
$2 = (LeftRight *) 0x3bf87c
```

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=18861
Approved-By: Tom Tromey <tom@tromey.com>
This commit is contained in:
Hannes Domani
2024-03-20 18:02:06 +01:00
parent e8f6050cfb
commit 23cdd9431a
3 changed files with 27 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
gdb/testsuite/gdb.cp/casts.cc
View File

@@ -88,6 +88,14 @@ main (int argc, char **argv)
unsigned long long gd_value = (unsigned long long) (std::uintptr_t)&gd;
unsigned long long r_value = (unsigned long long) (Right *) &gd;
LeftRight *lr = &gd;
Left *l = lr;
Right *r = lr;
LeftRight *lr_l = reinterpret_cast<LeftRight *>(l);
LeftRight *lr_r = reinterpret_cast<LeftRight *>(r);
Left *l_lr = reinterpret_cast<Left *>(lr);
Right *r_lr = reinterpret_cast<Right *>(lr);
VirtualLeftRight *vlr = new VirtualLeftRight ();
VirtualLeft *vl = vlr;
VirtualRight *vr = vlr;

10
gdb/testsuite/gdb.cp/casts.exp
View File

@@ -180,6 +180,16 @@ 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 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"
gdb_test "print reinterpret_cast<Right *>(lr) == r_lr" " = true"
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"
gdb_test "print &reinterpret_cast<Right &>(*lr) == r_lr" " = true"
gdb_test "print dynamic_cast<VirtualLeftRight *> (vlr) == vlr" " = true"
gdb_test "print dynamic_cast<VirtualLeftRight *> (vl) == vlr" " = true"
gdb_test "print dynamic_cast<VirtualLeftRight *> (vr) == vlr" " = true"

11
gdb/valops.c
View File

@@ -694,10 +694,17 @@ value_reinterpret_cast (struct type *type, struct value *arg)
|| (dest_code == TYPE_CODE_MEMBERPTR && arg_code == TYPE_CODE_INT)
|| (dest_code == TYPE_CODE_INT && arg_code == TYPE_CODE_MEMBERPTR)
|| (dest_code == arg_code
&& (dest_code == TYPE_CODE_PTR
|| dest_code == TYPE_CODE_METHODPTR
&& (dest_code == TYPE_CODE_METHODPTR
|| dest_code == TYPE_CODE_MEMBERPTR)))
result = value_cast (dest_type, arg);
else if (dest_code == TYPE_CODE_PTR && arg_code == TYPE_CODE_PTR)
{
/* Don't do any up- or downcasting. */
result = arg->copy ();
result->deprecated_set_type (dest_type);
result->set_enclosing_type (dest_type);
result->set_pointed_to_offset (0);
}
else
error (_("Invalid reinterpret_cast"));