fuchsia: fix bits/signal.h types

Fix definition of types in x86_64. `mcontext_t` provided opaque
field. `ucontext_t` had a slightly wrong definition. New records have
been introduced. They are particular to `mcontext_t`.

Add definitions in AArch64 and RISC-V64. They were missing. They are
different for all three target architectures.

These are declared in [1].

[1]: https://cs.opensource.google/fuchsia/fuchsia/+/main:zircon/third_party/ulib/musl/include/bits/signal.h

Author: dybucc

src/fuchsia/aarch64.rs

@@ -71,6 +71,25 @@ s! {
         __unused1: Padding<c_ulong>,
         __unused2: Padding<c_ulong>,
     }
+
+    // FIXME(f128): __reserved is meant to be an array of `long double`s. That
+    // requires native support for `f128`. This is currently missing.
+    pub struct mcontext_t {
+        pub fault_address: c_ulong,
+        pub regs: [c_ulong; 31],
+        pub sp: c_ulong,
+        pub pc: c_ulong,
+        pub pstate: c_ulong,
+        __reserved: Padding<[i128; 256]>,
+    }
+
+    pub struct ucontext_t {
+        pub uc_flags: c_ulong,
+        pub uc_link: *mut crate::ucontext_t,
+        pub uc_stack: crate::stack_t,
+        pub uc_sigmask: crate::sigset_t,
+        pub uc_mcontext: crate::mcontext_t,
+    }
 }
 
 // From https://cs.opensource.google/fuchsia/fuchsia/+/main:zircon/third_party/ulib/musl/include/bits/signal.h;l=20-21;drc=0827b18ab9540c46f8037f407d17ea15a79e9ba7

src/fuchsia/riscv64.rs

@@ -51,4 +51,16 @@ s! {
         __unused1: Padding<c_ulong>,
         __unused2: Padding<c_ulong>,
     }
+
+    pub struct mcontext_t {
+        pub regs: [c_ulong; 32],
+    }
+
+    pub struct ucontext_t {
+        pub uc_flags: c_ulong,
+        pub uc_link: *mut crate::ucontext_t,
+        pub uc_stack: crate::stack_t,
+        pub uc_sigmask: crate::sigset_t,
+        pub uc_mcontext: crate::mcontext_t,
+    }
 }

src/fuchsia/x86_64.rs

@@ -7,7 +7,34 @@ use crate::prelude::*;
 )]
 pub type __u64 = c_ulonglong;
 
+pub type gregset_t = [c_ulonglong; 23];
+pub type fpregset_t = *mut _fpstate;
+
 s! {
+    pub struct _fpstate {
+        pub cwd: c_ushort,
+        pub swd: c_ushort,
+        pub ftw: c_ushort,
+        pub fop: c_ushort,
+        pub rip: c_ulonglong,
+        pub rdp: c_ulonglong,
+        pub mxcsr: c_uint,
+        pub mxcr_mask: c_uint,
+        pub _st: [__c_anonymous__fpstate__st; 8],
+        pub _xmm: [__c_anonymous__fpstate__xmm; 16],
+        padding: Padding<[c_uint; 24]>,
+    }
+
+    pub struct __c_anonymous__fpstate__st {
+        pub significand: [c_ushort; 4],
+        pub exponent: c_ushort,
+        padding: Padding<[c_ushort; 3]>,
+    }
+
+    pub struct __c_anonymous__fpstate__xmm {
+        pub element: [c_uint; 4],
+    }
+
     pub struct stat {
         pub st_dev: crate::dev_t,
         pub st_ino: crate::ino_t,
@@ -55,7 +82,18 @@ s! {
     }
 
     pub struct mcontext_t {
-        __private: [u64; 32],
+        pub gregs: crate::gregset_t,
+        pub fpregs: crate::fpregset_t,
+        __reserved1: Padding<[c_ulonglong; 8]>,
+    }
+
+    pub struct ucontext_t {
+        pub uc_flags: c_ulong,
+        pub uc_link: *mut ucontext_t,
+        pub uc_stack: crate::stack_t,
+        pub uc_mcontext: crate::mcontext_t,
+        pub uc_sigmask: crate::sigset_t,
+        __fpregs_mem: [c_ulong; 64],
     }
 
     #[deprecated(
@@ -73,15 +111,6 @@ s! {
         __unused1: Padding<c_long>,
         __unused2: Padding<c_long>,
     }
-
-    pub struct ucontext_t {
-        pub uc_flags: c_ulong,
-        pub uc_link: *mut ucontext_t,
-        pub uc_stack: crate::stack_t,
-        pub uc_mcontext: mcontext_t,
-        pub uc_sigmask: crate::sigset_t,
-        __private: [u8; 512],
-    }
 }
 
 // offsets in user_regs_structs, from sys/reg.h