[PATCH] ld: Avoid folding new and delete pairs

[H.J. Lu]

On Mon, Jul 1, 2024, 4:43 PM Jonathan Wakely <jwakely@redhat.com> wrote:

> On 29/06/24 22:42 -0700, H.J. Lu wrote:
> >GCC 15 may fold new and delete pairs, like
> >
> >  A *bb = new A[10];
> >  delete [] bb;
> >  bb = new (std::nothrow) A [10];
> >  delete [] bb;
> >
> >as shown in
> >
> >https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115712
> >
> >Avoid folding new and delete pairs by adding a function call between new
> >and delete.
> >
> >       * testsuite/ld-elf/dl5.cc: Include "dl5.h".
> >       (A): Removed.
> >       Call foo between new and delete.
> >       * testsuite/ld-elf/dl5.h: New file.
> >       * testsuite/ld-elf/new.cc: Include "dl5.h".
> >       (foo): New function.
> >
> >Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> >---
> > ld/testsuite/ld-elf/dl5.cc | 13 +++----------
> > ld/testsuite/ld-elf/dl5.h  | 10 ++++++++++
> > ld/testsuite/ld-elf/new.cc |  6 ++++++
> > 3 files changed, 19 insertions(+), 10 deletions(-)
> > create mode 100644 ld/testsuite/ld-elf/dl5.h
> >
> >diff --git a/ld/testsuite/ld-elf/dl5.cc b/ld/testsuite/ld-elf/dl5.cc
> >index cc404553f93..77dbb62f3d5 100644
> >--- a/ld/testsuite/ld-elf/dl5.cc
> >+++ b/ld/testsuite/ld-elf/dl5.cc
> >@@ -1,6 +1,7 @@
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <new>
> >+#include "dl5.h"
> >
> > int pass = 0;
> >
> >@@ -30,22 +31,14 @@ operator delete (void *ptr) throw ()
> >     free (ptr);
> > }
> >
> >-class A
> >-{
> >-public:
> >-  A() {}
> >-  ~A() { }
> >-  int a;
> >-  int b;
> >-};
> >-
> >-
> > int
> > main (void)
> > {
> >   A *bb = new A[10];
> >   delete [] bb;
> >+  foo (bb);
>
> Shouldn't this call be *before* deleting the memory? bb is an invalid
> pointer value at this point, and so copying it to initialize the
> parameter of foo(A*) has implementation-defined behaviour. It's fine
> with GCC, but could in theory trap for some implementations.
>

I checked in a fix.

Thanks.


>
> >   bb = new (std::nothrow) A [10];
> >+  foo (bb);
> >   delete [] bb;
> >
> >   if (pass == 4)
> >diff --git a/ld/testsuite/ld-elf/dl5.h b/ld/testsuite/ld-elf/dl5.h
> >new file mode 100644
> >index 00000000000..0d4a7c1bfa3
> >--- /dev/null
> >+++ b/ld/testsuite/ld-elf/dl5.h
> >@@ -0,0 +1,10 @@
> >+class A
> >+{
> >+public:
> >+  A() {}
> >+  ~A() { }
> >+  int a;
> >+  int b;
> >+};
> >+
> >+extern void foo (A *);
> >diff --git a/ld/testsuite/ld-elf/new.cc b/ld/testsuite/ld-elf/new.cc
> >index 513cf2f3ad6..b038d770c6d 100644
> >--- a/ld/testsuite/ld-elf/new.cc
> >+++ b/ld/testsuite/ld-elf/new.cc
> >@@ -1,4 +1,5 @@
> > #include <new>
> >+#include "dl5.h"
> >
> > using std::bad_alloc;
> >
> >@@ -45,3 +46,8 @@ operator new[] (std::size_t sz, const std::nothrow_t&
> nothrow) throw()
> > {
> >   return ::operator new(sz, nothrow);
> > }
> >+
> >+void
> >+foo (A *)
> >+{
> >+}
> >--
> >2.45.2
> >
>
>
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