Re: [patch] Fix LD_PRELOAD=/usr/lib64/libasan.so.6 gdb

[Jan Kratochvil <jan.kratochvil@redhat.com>]

On Sun, 02 May 2021 15:39:12 +0200, Simon Marchi wrote:
> Please make sure to include all the relevant information about the issue
> you observed in the commit message.  It's really not clear by reading it
> what's the problem and why your change fixes it.

I was not aware GDB has changed the commit log format:

------------------------------------------------------------------------------

Currently for a binary compiled normally (without -fsanitize=address) but with
LD_PRELOAD of ASAN one gets:

$ ASAN_OPTIONS=detect_leaks=0:alloc_dealloc_mismatch=1:abort_on_error=1:fast_unwind_on_malloc=0 LD_PRELOAD=/usr/lib64/libasan.so.6 gdb
=================================================================
==1909567==ERROR: AddressSanitizer: alloc-dealloc-mismatch (malloc vs operator delete []) on 0x602000001570
    #0 0x7f1c98e5efa7 in operator delete[](void*) (/usr/lib64/libasan.so.6+0xb0fa7)
...
0x602000001570 is located 0 bytes inside of 2-byte region [0x602000001570,0x602000001572)
allocated by thread T0 here:
    #0 0x7f1c98e5cd1f in __interceptor_malloc (/usr/lib64/libasan.so.6+0xaed1f)
    #1 0x557ee4a42e81 in operator new(unsigned long) (/usr/libexec/gdb+0x74ce81)
SUMMARY: AddressSanitizer: alloc-dealloc-mismatch (/usr/lib64/libasan.so.6+0xb0fa7) in operator delete[](void*)
==1909567==HINT: if you don't care about these errors you may set ASAN_OPTIONS=alloc_dealloc_mismatch=0
==1909567==ABORTING

Despite the code called properly operator new[] and operator delete[].
But GDB's new-op.cc provides its own operator new[] which gets translated into
malloc() (which gets recongized as operatore new(size_t)) but as it does not
translate also operators delete[] Address Sanitizer gets confused.

The question is how many variants of the delete operator need to be provided.
Currently GDB does not call the nothrow delete operators (but it calls nothrow
new operators).

gdbsupport/
2021-05-02  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* new-op.cc (opertor delete 6x): New.

diff --git a/gdbsupport/new-op.cc b/gdbsupport/new-op.cc
index 5ab19621a43..f70d3ef191d 100644
--- a/gdbsupport/new-op.cc
+++ b/gdbsupport/new-op.cc
@@ -92,4 +92,44 @@ operator new[] (std::size_t sz, const std::nothrow_t&) noexcept
 {
   return ::operator new (sz, std::nothrow);
 }
+
+/* Define also operators delete as one can LD_PRELOAD=libasan.so.*
+   without recompiling the program with -fsanitize=address . */
+
+void
+operator delete (void *p)
+{
+  free (p);
+}
+
+void
+operator delete (void *p, const std::nothrow_t&) noexcept
+{
+  return ::operator delete (p);
+}
+
+void
+operator delete (void *p, std::size_t) noexcept
+{
+  return ::operator delete (p, std::nothrow);
+}
+
+void
+operator delete[] (void *p)
+{
+  return ::operator delete (p);
+}
+
+void
+operator delete[] (void *p, const std::nothrow_t&) noexcept
+{
+  return ::operator delete (p, std::nothrow);
+}
+
+void
+operator delete[] (void *p, std::size_t) noexcept
+{
+  return ::operator delete[] (p, std::nothrow);
+}
+
 #endif