libstdc++: Fix incorrect size calculation in PMR resource (PR 94906)

Calculating the size of a chunk being returned to the upstream allocator
was done with a 32-bit type, so it wrapped if the chunk was 4GB or
larger.

I don't know how to test this without allocating 4GB, so there's no test
in the testsuite. It has been tested manually of course.

Backport from mainline
2020-05-04  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/94906
	* src/c++17/memory_resource.cc
	(monotonic_buffer_resource::_Chunk::release): Use size_t for shift
	operands.

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index b37c19ace3b796711bcc60b4e1057927f40b28f1..d9c2ecf1ed471510c9067c668c41f527436c25d7 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,13 @@
 2020-05-12  Jonathan Wakely  <jwakely@redhat.com>
 
+       Backport from mainline
+       2020-05-04  Jonathan Wakely  <jwakely@redhat.com>
+
+       PR libstdc++/94906
+       * src/c++17/memory_resource.cc
+       (monotonic_buffer_resource::_Chunk::release): Use size_t for shift
+       operands.
+
        Backport from mainline
        2020-05-03  Jonathan Wakely  <jwakely@redhat.com>
 

diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc
index 56a87844da034b0aa51603291200c0557332ba06..70c39881fa1b99bff089eb4c3de012942e3a3fc1 100644 (file)
--- a/libstdc++-v3/src/c++17/memory_resource.cc
+++ b/libstdc++-v3/src/c++17/memory_resource.cc
@@ -228,8 +228,8 @@ namespace pmr
          if (__ch->_M_canary != (__ch->_M_size | __ch->_M_align))
            return; // buffer overflow detected!
 
-         size_t __size = (1u << __ch->_M_size);
-         size_t __align = (1u << __ch->_M_align);
+         size_t __size = (size_t)1 << __ch->_M_size;
+         size_t __align = (size_t)1 << __ch->_M_align;
          void* __start = (char*)(__ch + 1) - __size;
          __r->deallocate(__start, __size, __align);
        }