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Add a guard page for each thread

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This commit is contained in:
LemonBoy 2019-05-28 18:26:38 +02:00
parent 594366a482
commit 381f845287
1 changed files with 24 additions and 9 deletions
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33
std/thread.zig
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@ -223,15 +223,17 @@ pub const Thread = struct {
}
};
const MAP_GROWSDOWN = if (os.linux.is_the_target) os.linux.MAP_GROWSDOWN else 0;
var guard_end_offset: usize = undefined;
var stack_end_offset: usize = undefined;
var thread_start_offset: usize = undefined;
var context_start_offset: usize = undefined;
var tls_start_offset: usize = undefined;
const mmap_len = blk: {
// First in memory will be the stack, which grows downwards.
var l: usize = mem.alignForward(default_stack_size, mem.page_size);
var l: usize = mem.page_size;
// Allocate a guard page right after the end of the stack region
guard_end_offset = l;
// The stack itself, which grows downwards.
l = mem.alignForward(l + default_stack_size, mem.page_size);
stack_end_offset = l;
// Above the stack, so that it can be in the same mmap call, put the Thread object.
l = mem.alignForward(l, @alignOf(Thread));
@ -253,20 +255,33 @@ pub const Thread = struct {
}
break :blk l;
};
// Map the whole stack with no rw permissions to avoid committing the
// whole region right away
const mmap_slice = os.mmap(
null,
mem.alignForward(mmap_len, mem.page_size),
os.PROT_READ | os.PROT_WRITE,
os.MAP_PRIVATE | os.MAP_ANONYMOUS | MAP_GROWSDOWN,
os.PROT_NONE,
os.MAP_PRIVATE | os.MAP_ANONYMOUS,
-1,
0,
) catch |err| switch (err) {
error.MemoryMappingNotSupported => unreachable, // no file descriptor
error.AccessDenied => unreachable, // no file descriptor
error.PermissionDenied => unreachable, // no file descriptor
error.MemoryMappingNotSupported => unreachable,
error.AccessDenied => unreachable,
error.PermissionDenied => unreachable,
else => |e| return e,
};
errdefer os.munmap(mmap_slice);
// Map everything but the guard page as rw
os.mprotect(
mmap_slice,
os.PROT_READ | os.PROT_WRITE,
) catch |err| switch (err) {
error.OutOfMemory => unreachable,
error.AccessDenied => unreachable,
else => |e| return e,
};
const mmap_addr = @ptrToInt(mmap_slice.ptr);
const thread_ptr = @alignCast(@alignOf(Thread), @intToPtr(*Thread, mmap_addr + thread_start_offset));