Add signalfd support (#5322)

* add signalfd_siginfo to linux bits

* Cast sigaddset's shift value to u5

* linux: add signalfd4

* os: add signalfd

2 files changed, 39 insertions, 1 deletions

diff --git a/lib/std/os/bits/linux.zig b/lib/std/os/bits/linux.zig
index 64832673f1..41d681554e 100644
--- a/lib/std/os/bits/linux.zig
+++ b/lib/std/os/bits/linux.zig
@@ -840,6 +840,31 @@ pub const SIG_IGN = @intToPtr(?Sigaction.sigaction_fn, 1);
 
 pub const empty_sigset = [_]u32{0} ** sigset_t.len;
 
+pub const signalfd_siginfo = extern struct {
+    signo: u32,
+    errno: i32,
+    code: i32,
+    pid: u32,
+    uid: u32,
+    fd: i32,
+    tid: u32,
+    band: u32,
+    overrun: u32,
+    trapno: u32,
+    status: i32,
+    int: i32,
+    ptr: u64,
+    utime: u64,
+    stime: u64,
+    addr: u64,
+    addr_lsb: u16,
+    __pad2: u16,
+    syscall: i32,
+    call_addr: u64,
+    arch: u32,
+    __pad: [28]u8,
+};
+
 pub const in_port_t = u16;
 pub const sa_family_t = u16;
 pub const socklen_t = u32;
diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index 3b8df3d173..15d6e53c1e 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -811,7 +811,10 @@ pub fn sigaction(sig: u6, noalias act: *const Sigaction, noalias oact: ?*Sigacti
 
 pub fn sigaddset(set: *sigset_t, sig: u6) void {
     const s = sig - 1;
-    (set.*)[@intCast(usize, s) / usize.bit_count] |= @intCast(usize, 1) << (s & (usize.bit_count - 1));
+    // shift in musl: s&8*sizeof *set->__bits-1
+    const shift = @intCast(u5, s & (usize.bit_count - 1));
+    const val = @intCast(u32, 1) << shift;
+    (set.*)[@intCast(usize, s) / usize.bit_count] |= val;
 }
 
 pub fn sigismember(set: *const sigset_t, sig: u6) bool {
@@ -1197,6 +1200,16 @@ pub fn ioctl(fd: fd_t, request: u32, arg: usize) usize {
     return syscall3(.ioctl, @bitCast(usize, @as(isize, fd)), request, arg);
 }
 
+pub fn signalfd4(fd: fd_t, mask: *const sigset_t, flags: i32) usize {
+    return syscall4(
+        .signalfd4,
+        @bitCast(usize, @as(isize, fd)),
+        @ptrToInt(mask),
+        @bitCast(usize, @as(usize, NSIG / 8)),
+        @intCast(usize, flags),
+    );
+}
+
 test "" {
     if (builtin.os.tag == .linux) {
         _ = @import("linux/test.zig");