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https://github.com/yuzu-emu/unicorn.git
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22e3feb162
Unfold parts of qemu_ram_mmap() for the sake of understanding, moving declarations to the top, and keeping architecture-specifics in the ifdef-else blocks. No changes in the function behaviour. Give ptr and ptr1 meaningful names: ptr -> guardptr : pointer to the PROT_NONE guard region ptr1 -> ptr : pointer to the mapped memory returned to caller Backports commit 2044c3e7116eeac0449dcb4a4130cc8f8b9310da from qemu
100 lines
2.7 KiB
C
100 lines
2.7 KiB
C
/*
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* Support for RAM backed by mmaped host memory.
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*
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* Copyright (c) 2015 Red Hat, Inc.
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*
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* Authors:
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* Michael S. Tsirkin <mst@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or
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* later. See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "qemu/mmap-alloc.h"
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#include "qemu/host-utils.h"
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#include <sys/mman.h>
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void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
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{
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int flags;
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int guardfd;
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size_t offset;
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size_t total;
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void *guardptr;
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void *ptr;
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/*
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* Note: this always allocates at least one extra page of virtual address
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* space, even if size is already aligned.
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*/
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total = size + align;
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#if defined(__powerpc64__) && defined(__linux__)
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/* On ppc64 mappings in the same segment (aka slice) must share the same
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* page size. Since we will be re-allocating part of this segment
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* from the supplied fd, we should make sure to use the same page size, to
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* this end we mmap the supplied fd. In this case, set MAP_NORESERVE to
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* avoid allocating backing store memory.
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* We do this unless we are using the system page size, in which case
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* anonymous memory is OK.
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*/
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flags = MAP_PRIVATE;
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if (fd == -1 || qemu_fd_getpagesize(fd) == getpagesize()) {
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guardfd = -1;
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flags |= MAP_ANONYMOUS;
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} else {
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guardfd = fd;
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flags |= MAP_NORESERVE;
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}
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#else
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guardfd = -1;
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flags = MAP_PRIVATE | MAP_ANONYMOUS;
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#endif
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guardptr = mmap(0, total, PROT_NONE, flags, guardfd, 0);
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if (guardptr == MAP_FAILED) {
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return MAP_FAILED;
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}
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/* Make sure align is a power of 2 */
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assert(is_power_of_2(align));
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/* Always align to host page size */
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assert(align >= getpagesize());
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flags = MAP_FIXED;
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flags |= fd == -1 ? MAP_ANONYMOUS : 0;
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flags |= shared ? MAP_SHARED : MAP_PRIVATE;
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offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
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ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, flags, fd, 0);
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if (ptr == MAP_FAILED) {
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munmap(guardptr, total);
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return MAP_FAILED;
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}
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if (offset > 0) {
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munmap(guardptr, offset);
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}
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/*
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* Leave a single PROT_NONE page allocated after the RAM block, to serve as
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* a guard page guarding against potential buffer overflows.
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*/
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total -= offset;
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if (total > size + getpagesize()) {
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munmap(ptr + size + getpagesize(), total - size - getpagesize());
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}
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return ptr;
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}
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void qemu_ram_munmap(void *ptr, size_t size)
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{
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if (ptr) {
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/* Unmap both the RAM block and the guard page */
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munmap(ptr, size + getpagesize());
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}
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}
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