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util: exclude mmap-alloc.c from compilation target on Emscripten

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Emscripten does not support partial unmapping of mmapped memory
regions[1]. This limitation prevents correct implementation of qemu_ram_mmap
and qemu_ram_munmap, which rely on partial unmap behavior.

As a workaround, this commit excludes mmap-alloc.c from the Emscripten
build. Instead, for Emscripten build, this modifies qemu_anon_ram_alloc to
use qemu_memalign in place of qemu_ram_mmap, and disable memory backends
that rely on mmap, such as memory-backend-file and memory-backend-shm.

[1] d4a74336f2/system/lib/libc/emscripten_mmap.c (L61)

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>
Link: https://lore.kernel.org/r/76834f933ee4f14eeb5289d21c59d306886e58e9.1745820062.git.ktokunaga.mail@gmail.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Kohei Tokunaga 2025-04-28 15:39:05 +09:00 • committed by Paolo Bonzini
parent 1a89644240
commit 8e72b0eb18
5 changed files with 41 additions and 8 deletions
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9
system/physmem.c
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@ -1243,7 +1243,7 @@ long qemu_maxrampagesize(void)
return pagesize;
}
#ifdef CONFIG_POSIX
#if defined(CONFIG_POSIX) && !defined(EMSCRIPTEN)
static int64_t get_file_size(int fd)
{
int64_t size;
@ -1978,7 +1978,7 @@ out_free:
}
}
#ifdef CONFIG_POSIX
#if defined(CONFIG_POSIX) && !defined(EMSCRIPTEN)
RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, ram_addr_t max_size,
qemu_ram_resize_cb resized, MemoryRegion *mr,
uint32_t ram_flags, int fd, off_t offset,
@ -2158,7 +2158,8 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
assert(!host ^ (ram_flags & RAM_PREALLOC));
assert(max_size >= size);
#ifdef CONFIG_POSIX /* ignore RAM_SHARED for Windows */
/* ignore RAM_SHARED for Windows and emscripten*/
#if defined(CONFIG_POSIX) && !defined(EMSCRIPTEN)
if (!host) {
if (!share_flags && current_machine->aux_ram_share) {
ram_flags |= RAM_SHARED;
@ -2255,7 +2256,7 @@ static void reclaim_ramblock(RAMBlock *block)
;
} else if (xen_enabled()) {
xen_invalidate_map_cache_entry(block->host);
#ifndef _WIN32
#if !defined(_WIN32) && !defined(EMSCRIPTEN)
} else if (block->fd >= 0) {
qemu_ram_munmap(block->fd, block->host, block->max_length);
close(block->fd);