Shim ucontext_t to fix alignment issues on aarch64 mac

lib/vm/src/trap/traphandlers.rs

@@ -107,6 +107,70 @@ cfg_if::cfg_if! {
  static mut PREV_SIGILL: MaybeUninit<libc::sigaction> = MaybeUninit::uninit();
  static mut PREV_SIGFPE: MaybeUninit<libc::sigaction> = MaybeUninit::uninit();
 
+ cfg_if::cfg_if! {
+ if #[cfg(all(
+ target_pointer_width = "64",
+ any(
+ target_os = "macos",
+ target_os = "ios",
+ target_os = "tvos",
+ target_os = "watchos"
+ )
+ ))]
+ {
+ struct Darwin_mcontext64 {
+ __es: Darwin_arm_exception_state64,
+ __ss: Darwin_arm_thread_state64,
+ __ns: Darwin_arm_neon_state64,
+ }
+
+ struct Darwin_arm_exception_state64 {
+ __far: u64,
+ __esr: u32,
+ __exception: u32,
+ }
+
+ struct Darwin_arm_thread_state64 {
+ __x: [u64; 29],
+ __fp: u64,
+ __lr: u64,
+ __sp: u64,
+ __pc: u64,
+ __cpsr: u32,
+ __pad: u32,
+ }
+
+ #[repr(C, align(16))]
+ struct Darwin_arm_neon_state64 {
+ __v: [[u64; 2]; 32],
+ __fpsr: u32,
+ __fpcr: u32,
+ }
+
+ // We redefine [`libc::ucontext_t`] with one of its fields missing.
+ // <https://github.com/rust-lang/libc/issues/2812> introduced a fix
+ // for a segmentation fault in [`libc::getcontext`] that in turn broke
+ // the sigaction API, since it expects a pointer to a [`libc::ucontext_t`]
+ // type erased by a [`libc::c_void`] which aligns to 8 bytes, while
+ // [`libc::ucontext_t`] is aligned to 16 bytes with the change in the
+ // linked issue.
+ #[repr(C, align(8))]
+ struct Ucontext {
+ uc_onstack: libc::c_int,
+ uc_sigmask: libc::sigset_t,
+ uc_stack: libc::stack_t,
+ uc_link: *mut Ucontext,
+ uc_mcsize: usize,
+ uc_mcontext: *mut Darwin_mcontext64,
+ }
+ } else {
+ type Ucontext = libc::ucontext_t;
+ }
+ }
+
+ // Assert the alignment of [`Ucontext`] is compatible with the void ptr
+ const _: [(); std::mem::align_of::<*mut libc::c_void>() - std::mem::align_of::<Ucontext>()] = [];
+
  unsafe fn platform_init() {
  let register = |slot: &mut MaybeUninit<libc::sigaction>, signal: i32| {
  let mut handler: libc::sigaction = mem::zeroed();
@@ -216,7 +280,7 @@ cfg_if::cfg_if! {
  }
  _ => None,
  };
- let ucontext = &mut *(context as *mut libc::ucontext_t);
+ let ucontext = &mut *(context as *mut Ucontext);
  let (pc, sp) = get_pc_sp(ucontext);
  let handled = TrapHandlerContext::handle_trap(
  pc,
@@ -256,7 +320,7 @@ cfg_if::cfg_if! {
  }
  }
 
- unsafe fn get_pc_sp(context: &libc::ucontext_t) -> (usize, usize) {
+ unsafe fn get_pc_sp(context: &Ucontext) -> (usize, usize) {
  let (pc, sp);
  cfg_if::cfg_if! {
  if #[cfg(all(
@@ -308,7 +372,7 @@ cfg_if::cfg_if! {
  (pc, sp)
  }
 
- unsafe fn update_context(context: &mut libc::ucontext_t, regs: TrapHandlerRegs) {
+ unsafe fn update_context(context: &mut Ucontext, regs: TrapHandlerRegs) {
  cfg_if::cfg_if! {
  if #[cfg(all(
  any(target_os = "linux", target_os = "android"),