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runtime: Use a better heap location on arm64 systems.

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Before this, the heap location used on a 64-bit system was not
available to user-space on arm64, so the "32-bit" strategy ended up
being used.  So use somewhere that is available, and for bonus points
is far away from where the kernel allocates address space by default.

From-SVN: r207977
This commit is contained in:
Ian Lance Taylor 2014-02-21 03:24:03 +00:00
parent cc73e54dc6
commit 91d6f071fb
1 changed files with 27 additions and 3 deletions
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30
libgo/runtime/malloc.goc
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@ -27,6 +27,31 @@ package runtime
#define KindPtr GO_PTR
#define KindNoPointers GO_NO_POINTERS
// GCCGO SPECIFIC CHANGE
//
// There is a long comment in runtime_mallocinit about where to put the heap
// on a 64-bit system. It makes assumptions that are not valid on linux/arm64
// -- it assumes user space can choose the lower 47 bits of a pointer, but on
// linux/arm64 we can only choose the lower 39 bits. This means the heap is
// roughly a quarter of the available address space and we cannot choose a bit
// pattern that all pointers will have -- luckily the GC is mostly precise
// these days so this doesn't matter all that much. The kernel (as of 3.13)
// will allocate address space starting either down from 0x7fffffffff or up
// from 0x2000000000, so we put the heap roughly in the middle of these two
// addresses to minimize the chance that a non-heap allocation will get in the
// way of the heap.
//
// This all means that there isn't much point in trying 256 different
// locations for the heap on such systems.
#ifdef __aarch64__
#define HeapBase(i) ((void*)(uintptr)(0x40ULL<<32))
#define HeapBaseOptions 1
#else
#define HeapBase(i) ((void*)(uintptr)(i<<40|0x00c0ULL<<32))
#define HeapBaseOptions 0x80
#endif
// END GCCGO SPECIFIC CHANGE
// Mark mheap as 'no pointers', it does not contain interesting pointers but occupies ~45K.
MHeap runtime_mheap;
@ -423,9 +448,8 @@ runtime_mallocinit(void)
bitmap_size = arena_size / (sizeof(void*)*8/4);
spans_size = arena_size / PageSize * sizeof(runtime_mheap.spans[0]);
spans_size = ROUND(spans_size, PageSize);
for(i = 0; i <= 0x7f; i++) {
p = (void*)(uintptr)(i<<40 | 0x00c0ULL<<32);
p = runtime_SysReserve(p, bitmap_size + spans_size + arena_size);
for(i = 0; i < HeapBaseOptions; i++) {
p = runtime_SysReserve(HeapBase(i), bitmap_size + spans_size + arena_size);
if(p != nil)
break;
}