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cxx: Decouple C++ runtime from 'env()->heap()'

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This commit is contained in:
Norman Feske 2013-03-21 11:02:46 +01:00
parent 82aa092dac
commit 764a3656a1
1 changed files with 32 additions and 2 deletions
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34
base/src/base/cxx/malloc_free.cc
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@ -15,10 +15,40 @@
*/
#include <base/env.h>
#include <base/heap.h>
#include <util/string.h>
using namespace Genode;
/**
* Return heap partition for the private use within the cxx library.
*
* If we used the 'env()->heap()' with the C++ runtime, we would run into a
* deadlock when a 'Ram_session::Alloc_failed' exception is thrown from within
* 'Heap::alloc'. For creating the exception object, the C++ runtime calls
* '__cxa_allocate_exception', which, in turn, calls 'malloc'. If our 'malloc'
* implementation called 'env()->heap()->alloc()', we would end up in a
* recursive attempt to obtain the 'env()->heap()' lock.
*
* By using a dedicated heap instance for the cxx library, we avoid this
* circular condition.
*/
static Heap *cxx_heap()
{
/*
* Exception frames are small (ca. 100 bytes). Hence, a small static
* backing store suffices for the cxx heap partition in the normal
* case. The 'env()->ram_session' is used only if the demand exceeds
* the capacity of the 'initial_block'.
*/
static char initial_block[512];
static Heap heap(env()->ram_session(), env()->rm_session(),
Heap::UNLIMITED, initial_block, sizeof(initial_block));
return &heap;
}
typedef unsigned long Block_header;
@ -35,7 +65,7 @@ extern "C" void *malloc(unsigned size)
*/
unsigned long real_size = size + sizeof(Block_header);
void *addr = 0;
if (!Genode::env()->heap()->alloc(real_size, &addr))
if (!cxx_heap()->alloc(real_size, &addr))
return 0;
*(Block_header *)addr = real_size;
@ -56,7 +86,7 @@ extern "C" void free(void *ptr)
if (!ptr) return;
unsigned long *addr = ((unsigned long *)ptr) - 1;
Genode::env()->heap()->free(addr, *addr);
cxx_heap()->free(addr, *addr);
}