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| author | Tom Tromey <tom@tromey.com> | 2022-04-02 09:54:40 -0600 |
|---|---|---|
| committer | Tom Tromey <tom@tromey.com> | 2022-04-18 09:34:55 -0600 |
| commit | 2390419d1cb72882110538e01e5586372df19657 (patch) | |
| tree | 184695bb4127c296ef8c1305e48fca1c0e27fdfb | |
| parent | c67f4e53895da91ce7f2eff3544e9de02280f740 (diff) | |
| download | binutils-2390419d1cb72882110538e01e5586372df19657.zip binutils-2390419d1cb72882110538e01e5586372df19657.tar.gz binutils-2390419d1cb72882110538e01e5586372df19657.tar.bz2 | |
Fix C++ cast of derived class to base class
PR c++/28907 points out that casting from a derived class to a base
class fails in some situations. The problem turned out to be a
missing use of value_embedded_offset. One peculiarity here is that,
if you managed to construct a pointer-to-derived with an embedded
offset of 0, the cast would work -- for example, one of the two new
tests here passes without the patch.
This embedded offset stuff is an endless source of bugs. I wonder if
it's possible to get rid of it somehow.
Regression tested on x86-64 Fedora 34.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28907
| -rw-r--r-- | gdb/testsuite/gdb.cp/casts.cc | 20 | ||||
| -rw-r--r-- | gdb/testsuite/gdb.cp/casts.exp | 6 | ||||
| -rw-r--r-- | gdb/valops.c | 2 |
3 files changed, 27 insertions, 1 deletions
diff --git a/gdb/testsuite/gdb.cp/casts.cc b/gdb/testsuite/gdb.cp/casts.cc index 543db89..ea4dc96 100644 --- a/gdb/testsuite/gdb.cp/casts.cc +++ b/gdb/testsuite/gdb.cp/casts.cc @@ -34,6 +34,20 @@ struct DoublyDerived : public VirtuallyDerived, { }; +struct Left +{ + int left; +}; + +struct Right +{ + int right; +}; + +struct LeftRight : public Left, public Right +{ +}; + int main (int argc, char **argv) { @@ -48,5 +62,11 @@ main (int argc, char **argv) Alpha *ad = &derived; Alpha *add = &doublyderived; + LeftRight gd; + gd.left = 23; + gd.right = 27; + unsigned long long gd_value = (unsigned long long) &gd; + unsigned long long r_value = (unsigned long long) (Right *) &gd; + return 0; /* breakpoint spot: casts.exp: 1 */ } diff --git a/gdb/testsuite/gdb.cp/casts.exp b/gdb/testsuite/gdb.cp/casts.exp index cda870f..5d0a524 100644 --- a/gdb/testsuite/gdb.cp/casts.exp +++ b/gdb/testsuite/gdb.cp/casts.exp @@ -174,6 +174,12 @@ gdb_test "print dynamic_cast<Gamma *> (add)" \ " = \\(Gamma \\*\\) $nonzero_hex" \ "dynamic_cast to sibling" +gdb_test "print (unsigned long long) &gd == gd_value" " = true" +gdb_test "print (unsigned long long) (LeftRight *) (Right *) &gd == gd_value" \ + " = true" +gdb_test "print (unsigned long long) (LeftRight *) (Right *) r_value == gd_value" \ + " = true" + if {[prepare_for_testing "failed to prepare" ${testfile}03 $srcfile2 \ {debug c++ additional_flags=-std=c++03}]} { return -1 diff --git a/gdb/valops.c b/gdb/valops.c index 42a1213..e84cabf 100644 --- a/gdb/valops.c +++ b/gdb/valops.c @@ -274,7 +274,7 @@ value_cast_structs (struct type *type, struct value *v2) if (v) { /* Downcasting is possible (t1 is superclass of v2). */ - CORE_ADDR addr2 = value_address (v2); + CORE_ADDR addr2 = value_address (v2) + value_embedded_offset (v2); addr2 -= value_address (v) + value_embedded_offset (v); return value_at (type, addr2); |