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

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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.
This commit is contained in:
Jonathan Wakely
2020-05-12 09:54:44 +01:00
parent 89714e45f0
commit 45a6686e76
2 changed files with 12 additions and 2 deletions
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10
libstdc++-v3/ChangeLog
View File

@@ -1,3 +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.
2020-05-07 Eric Botcazou <ebotcazou@adacore.com>
* config/abi/post/sparc64-linux-gnu/baseline_symbols.txt: Update.

4
libstdc++-v3/src/c++17/memory_resource.cc
View File

@@ -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);
}