make flag checks reobust against multi-bit flags

Author: RalfJung

src/tools/miri/src/shims/unix/fs.rs

@@ -562,17 +562,17 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let mut mirror = access_mode;
 
         let o_append = this.eval_libc_i32("O_APPEND")?;
-        if flag & o_append != 0 {
+        if flag & o_append == o_append {
             options.append(true);
             mirror |= o_append;
         }
         let o_trunc = this.eval_libc_i32("O_TRUNC")?;
-        if flag & o_trunc != 0 {
+        if flag & o_trunc == o_trunc {
             options.truncate(true);
             mirror |= o_trunc;
         }
         let o_creat = this.eval_libc_i32("O_CREAT")?;
-        if flag & o_creat != 0 {
+        if flag & o_creat == o_creat {
             // Get the mode.  On macOS, the argument type `mode_t` is actually `u16`, but
             // C integer promotion rules mean that on the ABI level, it gets passed as `u32`
             // (see https://github.com/rust-lang/rust/issues/71915).
@@ -592,22 +592,22 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             mirror |= o_creat;
 
             let o_excl = this.eval_libc_i32("O_EXCL")?;
-            if flag & o_excl != 0 {
+            if flag & o_excl == o_excl {
                 mirror |= o_excl;
                 options.create_new(true);
             } else {
                 options.create(true);
             }
         }
         let o_cloexec = this.eval_libc_i32("O_CLOEXEC")?;
-        if flag & o_cloexec != 0 {
+        if flag & o_cloexec == o_cloexec {
             // We do not need to do anything for this flag because `std` already sets it.
             // (Technically we do not support *not* setting this flag, but we ignore that.)
             mirror |= o_cloexec;
         }
         if this.tcx.sess.target.os == "linux" {
             let o_tmpfile = this.eval_libc_i32("O_TMPFILE")?;
-            if flag & o_tmpfile != 0 {
+            if flag & o_tmpfile == o_tmpfile {
                 // if the flag contains `O_TMPFILE` then we return a graceful error
                 let eopnotsupp = this.eval_libc("EOPNOTSUPP")?;
                 this.set_last_error(eopnotsupp)?;
@@ -1020,7 +1020,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
         let path = this.read_path_from_c_str(pathname_ptr)?.into_owned();
         // See <https://github.com/rust-lang/rust/pull/79196> for a discussion of argument sizes.
-        let empty_path_flag = flags & this.eval_libc("AT_EMPTY_PATH")?.to_i32()? != 0;
+        let at_ampty_path = this.eval_libc_i32("AT_EMPTY_PATH")?;
+        let empty_path_flag = flags & at_ampty_path == at_ampty_path;
         // We only support:
         // * interpreting `path` as an absolute directory,
         // * interpreting `path` as a path relative to `dirfd` when the latter is `AT_FDCWD`, or

src/tools/miri/src/shims/unix/linux/sync.rs

@@ -90,7 +90,8 @@ pub fn futex<'tcx>(
             let timeout_time = if this.ptr_is_null(timeout.ptr)? {
                 None
             } else {
-                if op & futex_realtime != 0 {
+                let realtime = op & futex_realtime == futex_realtime;
+                if realtime {
                     this.check_no_isolation(
                         "`futex` syscall with `op=FUTEX_WAIT` and non-null timeout with `FUTEX_CLOCK_REALTIME`",
                     )?;
@@ -106,14 +107,14 @@ pub fn futex<'tcx>(
                 };
                 Some(if wait_bitset {
                     // FUTEX_WAIT_BITSET uses an absolute timestamp.
-                    if op & futex_realtime != 0 {
+                    if realtime {
                         Time::RealTime(SystemTime::UNIX_EPOCH.checked_add(duration).unwrap())
                     } else {
                         Time::Monotonic(this.machine.clock.anchor().checked_add(duration).unwrap())
                     }
                 } else {
                     // FUTEX_WAIT uses a relative timestamp.
-                    if op & futex_realtime != 0 {
+                    if realtime {
                         Time::RealTime(SystemTime::now().checked_add(duration).unwrap())
                     } else {
                         Time::Monotonic(this.machine.clock.now().checked_add(duration).unwrap())

src/tools/miri/src/shims/windows/foreign_items.rs

@@ -76,7 +76,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 this.read_scalar(handle)?.to_machine_isize(this)?;
                 let flags = this.read_scalar(flags)?.to_u32()?;
                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
-                let zero_init = (flags & 0x00000008) != 0; // HEAP_ZERO_MEMORY
+                let heap_zero_memory = 0x00000008; // HEAP_ZERO_MEMORY
+                let zero_init = (flags & heap_zero_memory) == heap_zero_memory;
                 let res = this.malloc(size, zero_init, MiriMemoryKind::WinHeap)?;
                 this.write_pointer(res, dest)?;
             }