Add prototype ucontext_t support.

src/platform/linux/signal.rs

@@ -14,6 +14,48 @@ use crate::{
     },
 };
 
+// Mirrors the ucontext_t struct from the libc crate on Linux.
+#[repr(C)]
+pub struct ucontext_t {
+    pub uc_flags: c_ulong,
+    pub uc_link: *mut ucontext_t,
+    pub uc_stack: stack_t,
+    pub uc_mcontext: mcontext_t,
+    pub uc_sigmask: sigset_t,
+    __private: [u8; 512],
+}
+#[repr(C)]
+pub struct _libc_fpstate {
+    pub cwd: u16,
+    pub swd: u16,
+    pub ftw: u16,
+    pub fop: u16,
+    pub rip: u64,
+    pub rdp: u64,
+    pub mxcsr: u32,
+    pub mxcr_mask: u32,
+    pub _st: [_libc_fpxreg; 8],
+    pub _xmm: [_libc_xmmreg; 16],
+    __private: [u64; 12],
+}
+#[repr(C)]
+pub struct _libc_fpxreg {
+    pub significand: [u16; 4],
+    pub exponent: u16,
+    __private: [u16; 3],
+}
+
+#[repr(C)]
+pub struct _libc_xmmreg {
+    pub element: [u32; 4],
+}
+#[repr(C)]
+pub struct mcontext_t {
+    pub gregs: [i64; 23], // TODO: greg_t?
+    pub fpregs: *mut _libc_fpstate,
+    __private: [u64; 8],
+}
+
 impl PalSignal for Sys {
     unsafe fn getitimer(which: c_int, out: *mut itimerval) -> c_int {
         e(syscall!(GETITIMER, which, out)) as c_int

src/platform/redox/signal.rs

@@ -1,5 +1,7 @@
-use core::mem;
-use redox_rt::signal::{Sigaction, SigactionFlags, SigactionKind, Sigaltstack, SignalHandler};
+use core::mem::{self, offset_of};
+use redox_rt::signal::{
+    SigStack, Sigaction, SigactionFlags, SigactionKind, Sigaltstack, SignalHandler,
+};
 use syscall::{self, Result};
 
 use super::{
@@ -20,6 +22,53 @@ use crate::{
     platform::ERRNO,
 };
 
+#[repr(C)]
+pub struct ucontext_t {
+    #[cfg(any(target_arch = "x86_64", target_arch = "aarch64"))]
+    _pad: [usize; 1], // pad from 7*8 to 64
+
+    #[cfg(target_arch = "x86")]
+    _pad: [usize; 0], // don't pad from 8*4
+
+    pub uc_link: *mut ucontext_t,
+    pub uc_stack: stack_t,
+    pub uc_sigmask: sigset_t,
+    _sival: usize,
+    _signum: usize,
+    pub uc_mcontext: mcontext_t,
+}
+
+const _: () = {
+    const fn assert_eq(a: usize, b: usize) {
+        if a != b {
+            panic!("compile-time struct verification failed");
+        }
+    }
+    assert_eq(offset_of!(ucontext_t, uc_link), offset_of!(SigStack, link));
+    assert_eq(
+        offset_of!(ucontext_t, uc_stack),
+        offset_of!(SigStack, old_stack),
+    );
+    assert_eq(
+        offset_of!(ucontext_t, uc_sigmask),
+        offset_of!(SigStack, old_mask),
+    );
+    assert_eq(
+        offset_of!(ucontext_t, uc_mcontext),
+        offset_of!(SigStack, regs),
+    );
+};
+
+#[repr(C)]
+pub struct mcontext_t {
+    #[cfg(target_arch = "x86")]
+    _opaque: [u8; 512],
+    #[cfg(target_arch = "x86-64")]
+    _opaque: [u8; 864],
+    #[cfg(target_arch = "aarch64")]
+    _opaque: [u8; 272],
+}
+
 impl PalSignal for Sys {
     unsafe fn getitimer(which: c_int, out: *mut itimerval) -> c_int {
         let path = match which {