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Fix crash on aarch64 linux. #225

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Fix crash on aarch64 linux. #225

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12bdfd2
Fix low memory allocation on aarch64 linux.
SegHaxx Nov 26, 2020
2dfd717
Don't break real addressing.
SegHaxx Nov 27, 2020
45e5b4e
SELinux on CentOS blocks the first 64k
SegHaxx Nov 27, 2020
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17 changes: 16 additions & 1 deletion BasiliskII/src/CrossPlatform/vm_alloc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,10 @@ typedef unsigned long vm_uintptr_t;
#define MAP_ANONYMOUS 0
#endif

/* NOTE: on linux MAP_32BIT is only implemented on AMD64
it is a null op on all other architectures
thus the MAP_BASE setting below is the only thing
ensuring low addresses on aarch64 for example */
#define MAP_EXTRA_FLAGS (MAP_32BIT)

#ifdef HAVE_MMAP_VM
Expand All @@ -91,7 +95,18 @@ typedef unsigned long vm_uintptr_t;
don't get addresses above when the program is run on AMD64.
NOTE: this is empirically determined on Linux/x86. */
#define MAP_BASE 0x10000000
#else
#elif !REAL_ADDRESSING
/* linux does not implement any useful fallback behavior
such as allocating the next available address
and the first 4k-64k of address space is marked unavailable
for security reasons (see https://wiki.debian.org/mmap_min_addr)
so we must start requesting after the first page
(or we get a high 64bit address and break on aarch64)

leaving NULL unmapped is a good idea anyway for debugging reasons
so we do this unconditionally on all platforms */
#define MAP_BASE 0x00010000
#else /* must be 0x0 when REAL_ADDRESSING=1 */
#define MAP_BASE 0x00000000
#endif
static char * next_address = (char *)MAP_BASE;
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