Add support for AArch64

close #43
This commit is contained in:
Amanieu d'Antras 2016-09-02 10:45:55 +01:00 committed by edef
parent fff625767c
commit 40e955638e
3 changed files with 249 additions and 4 deletions

View File

@ -115,7 +115,7 @@ there should be at least 8 KiB of free stack space, or panicking will result in
## Limitations
The architectures currently supported are: x86, x86_64, or1k.
The architectures currently supported are: x86, x86_64, aarch64, or1k.
The platforms currently supported are: bare metal, Linux (any libc),
FreeBSD, DragonFly BSD, macOS.

src/arch/ Normal file
View File

@ -0,0 +1,244 @@
// This file is part of libfringe, a low-level green threading library.
// Copyright (c) edef <>,
// whitequark <>
// Amanieu d'Antras <>
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
//> or the MIT license <LICENSE-MIT or
//>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.
// To understand the code in this file, keep in mind these two facts:
// * The iOS AArch64 ABI has a "red zone": 128 bytes under the top of the stack
// that is defined to be unmolested by signal handlers, interrupts, etc.
// Leaf functions can use the red zone without adjusting the stack pointer.
// * The AArch64 ABI requires the stack to always be a multiple of 16 bytes,
// even in the middle of functions. Aligned operands are a requirement
// of atomic operations, and making this the responsibility of the caller
// avoids having to maintain a frame pointer, which is necessary when
// a function has to realign the stack from an unknown state.
// * The AArch64 ABI passes the first argument in x0. We also use x0
// to pass a value while swapping context; this is an arbitrary choice
// (we clobber all registers and could use any of them) but this allows us
// to reuse the swap function to perform the initial call. We do the same
// thing with x1 to pass the stack pointer to the new context.
// To understand the DWARF CFI code in this file, keep in mind these facts:
// * CFI is "call frame information"; a set of instructions to a debugger or
// an unwinder that allow it to simulate returning from functions. This implies
// restoring every register to its pre-call state, as well as the stack pointer.
// * CFA is "call frame address"; the value of stack pointer right before the call
// instruction in the caller. Everything strictly below CFA (and inclusive until
// the next CFA) is the call frame of the callee. This implies that the return
// address is the part of callee's call frame.
// * Logically, DWARF CFI is a table where rows are instruction pointer values and
// columns describe where registers are spilled (mostly using expressions that
// compute a memory location as CFA+n). A .cfi_offset pseudoinstruction changes
// the state of a column for all IP numerically larger than the one it's placed
// after. A .cfi_def_* pseudoinstruction changes the CFA value similarly.
// * Simulating return is as easy as restoring register values from the CFI table
// and then setting stack pointer to CFA.
// A high-level overview of the function of the trampolines when unwinding is:
// * The 2nd init trampoline puts a controlled value (written in swap to `new_cfa`)
// into x29. This is then used as the CFA for the 1st trampoline.
// * This controlled value points to the bottom of the stack of the parent context,
// which holds the saved x29 and x30 from the call to swap().
// * The 1st init trampoline tells the unwinder to restore x29 and x30
// from the stack frame at x29 (in the parent stack), thus continuing
// unwinding at the swap call site instead of falling off the end of context stack.
use core::mem;
use stack::Stack;
pub const STACK_ALIGNMENT: usize = 16;
#[derive(Debug, Clone, Copy)]
pub struct StackPointer(*mut usize);
pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize, StackPointer) -> !) -> StackPointer {
#[cfg(not(target_vendor = "apple"))]
unsafe extern "C" fn trampoline_1() {
# gdb has a hardcoded check that rejects backtraces where frame addresses
# do not monotonically decrease. It is turned off if the function is called
# "__morestack" and that is hardcoded. So, to make gdb backtraces match
# the actual unwinder behavior, we call ourselves "__morestack" and mark
# the symbol as local; it shouldn't interfere with anything.
.local __morestack
# Set up the first part of our DWARF CFI linking stacks together. When
# we reach this function from unwinding, x29 will be pointing at the bottom
# of the parent linked stack. This link is set each time swap() is called.
# When unwinding the frame corresponding to this function, a DWARF unwinder
# will use x29+16 as the next call frame address, restore return address (x30)
# from CFA-8 and restore x29 from CFA-16. This mirrors what the second half
# of `swap_trampoline` does.
.cfi_def_cfa x29, 16
.cfi_offset x30, -8
.cfi_offset x29, -16
# This nop is here so that the initial swap doesn't return to the start
# of the trampoline, which confuses the unwinder since it will look for
# frame information in the previous symbol rather than this one. It is
# never actually executed.
.size __morestack, .Lend-__morestack
: : : : "volatile")
#[cfg(target_vendor = "apple")]
unsafe extern "C" fn trampoline_1() {
# Identical to the above, except avoids .local/.size that aren't available on Mach-O.
.private_extern __morestack
.cfi_def_cfa x29, 16
.cfi_offset x30, -8
.cfi_offset x29, -16
: : : : "volatile")
unsafe extern "C" fn trampoline_2() {
# Set up the second part of our DWARF CFI.
# When unwinding the frame corresponding to this function, a DWARF unwinder
# will restore x29 (and thus CFA of the first trampoline) from the stack slot.
# This stack slot is updated every time swap() is called to point to the bottom
# of the stack of the context switch just switched from.
.cfi_def_cfa x29, 16
.cfi_offset x30, -8
.cfi_offset x29, -16
# This nop is here so that the return address of the swap trampoline
# doesn't point to the start of the symbol. This confuses gdb's backtraces,
# causing them to think the parent function is trampoline_1 instead of
# trampoline_2.
# Call the provided function.
ldr x2, [sp, #16]
blr x2
: : : : "volatile")
unsafe fn push(sp: &mut StackPointer, val: usize) {
sp.0 = sp.0.offset(-1);
*sp.0 = val
// We set up the stack in a somewhat special way so that to the unwinder it
// looks like trampoline_1 has called trampoline_2, which has in turn called
// swap::trampoline.
// There are 2 call frames in this setup, each containing the return address
// followed by the x29 value for that frame. This setup supports unwinding
// using DWARF CFI as well as the frame pointer-based unwinding used by tools
// such as perf or dtrace.
let mut sp = StackPointer(stack.base() as *mut usize);
push(&mut sp, 0 as usize); // Padding to ensure the stack is properly aligned
push(&mut sp, f as usize); // Function that trampoline_2 should call
// Call frame for trampoline_2. The CFA slot is updated by swap::trampoline
// each time a context switch is performed.
push(&mut sp, trampoline_1 as usize + 4); // Return after the nop
push(&mut sp, 0xdeaddeaddead0cfa); // CFA slot
// Call frame for swap::trampoline. We set up the x29 value to point to the
// parent call frame.
let frame = sp;
push(&mut sp, trampoline_2 as usize + 4); // Entry point, skip initial nop
push(&mut sp, frame.0 as usize); // Pointer to parent call frame
pub unsafe fn swap(arg: usize, new_sp: StackPointer,
new_stack: Option<&Stack>) -> (usize, StackPointer) {
// Address of the topmost CFA stack slot.
let mut dummy: usize = mem::uninitialized();
let new_cfa = if let Some(new_stack) = new_stack {
(new_stack.base() as *mut usize).offset(-4)
} else {
// Just pass a dummy pointer if we aren't linking the stack
&mut dummy
unsafe extern "C" fn trampoline() {
# Save the frame pointer and link register; the unwinder uses them to find
# the CFA of the caller, and so they have to have the correct value immediately
# after the call instruction that invoked the trampoline.
stp x29, x30, [sp, #-16]!
.cfi_adjust_cfa_offset 16
.cfi_rel_offset x30, 8
.cfi_rel_offset x29, 0
# Link the call stacks together by writing the current stack bottom
# address to the CFA slot in the new stack.
mov x4, sp
str x4, [x3]
# Pass the stack pointer of the old context to the new one.
mov x1, sp
# Load stack pointer of the new context.
mov sp, x2
# Load frame and instruction pointers of the new context.
ldp x29, x30, [sp], #16
.cfi_adjust_cfa_offset -16
.cfi_restore x29
.cfi_restore x30
# Return into the new context. Use `br` instead of a `ret` to avoid
# return address mispredictions.
br x30
: : : : "volatile")
let ret: usize;
let ret_sp: *mut usize;
# Call the trampoline to switch to the new context.
bl ${2}
: "={x0}" (ret)
"={x1}" (ret_sp)
: "s" (trampoline as usize)
"{x0}" (arg)
"{x2}" (new_sp.0)
"{x3}" (new_cfa)
:/*x0, "x1",*/"x2", "x3", "x4", "x5", "x6", "x7",
"x8", "x9", "x10", "x11", "x12", "x13", "x14", "x15",
"x16", "x17", "x18", "x19", "x20", "x21", "x22", "x23",
"x24", "x25", "x26", "x27", "x28",/*fp,*/ "lr", /*sp,*/
"v0", "v1", "v2", "v3", "v4", "v5", "v6", "v7",
"v8", "v9", "v10", "v11", "v12", "v13", "v14", "v15",
"v16", "v17", "v18", "v19", "v20", "v21", "v22", "v23",
"v24", "v25", "v26", "v27", "v28", "v29", "v30", "v31",
"cc", "memory"
// Ideally, we would set the LLVM "noredzone" attribute on this function
// (and it would be propagated to the call site). Unfortunately, rustc
// provides no such functionality. Fortunately, by a lucky coincidence,
// the "alignstack" LLVM inline assembly option does exactly the same
// thing on AArch64.
: "volatile", "alignstack");
(ret, StackPointer(ret_sp))

View File

@ -9,9 +9,10 @@
pub use self::imp::*;
#[allow(unused_attributes)] // rust-lang/rust#35584
#[cfg_attr(target_arch = "x86", path = "")]
#[cfg_attr(target_arch = "x86_64", path = "")]
#[cfg_attr(target_arch = "or1k", path = "")]
#[cfg_attr(target_arch = "x86", path = "")]
#[cfg_attr(target_arch = "x86_64", path = "")]
#[cfg_attr(target_arch = "aarch64", path = "")]
#[cfg_attr(target_arch = "or1k", path = "")]
mod imp;