Add a platform-specific syscall number iterator.

sandbox/linux/seccomp-bpf/syscall_iterator.cc

Index: sandbox/linux/seccomp-bpf/syscall_iterator.cc
diff --git a/sandbox/linux/seccomp-bpf/syscall_iterator.cc b/sandbox/linux/seccomp-bpf/syscall_iterator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f15febe798c0b0d2eb4a6e4ac68185ee2bbb7f8b
--- /dev/null
+++ b/sandbox/linux/seccomp-bpf/syscall_iterator.cc
@@ -0,0 +1,91 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
+#include "sandbox/linux/seccomp-bpf/syscall_iterator.h"
+
+namespace playground2 {
+
+uint32_t SyscallIterator::Next() {
+  if (done_) {
+    return num_;
+  }
+
+  uint32_t val;
+  do {
+    // |num_| has been initialized to MIN_SYSCALL, which we assume is 0.

[jln (very slow on Chromium), 2012/10/13 17:44:55]

See my comment in the .h file. I think the comment should look more like what I
had written before.

We first return 0, because this is what the interlace promises we'll do. Since 0
is also conveniently MIN_SYSCALL, this simplifies a bunch of things.

[Jorge Lucangeli Obes, 2012/10/15 17:25:36]

Done.

+    // This true for supported architectures (Intel and ARM EABI).
+    CHECK_EQ(MIN_SYSCALL, 0u);
+    val = num_;
+
+    // First we iterate up to MAX_PUBLIC_SYSCALL, which is equal to MAX_SYSCALL
+    // on Intel architectures, but leaves room for private syscalls on ARM.
+    if (num_ <= MAX_PUBLIC_SYSCALL) {
+      if (invalid_only_ && num_ < MAX_PUBLIC_SYSCALL) {
+        num_ = MAX_PUBLIC_SYSCALL;
+      } else {
+        ++num_;
+      }
+#if defined(__arm__)
+    // ARM EABI includes "ARM private" system calls starting at
+    // MIN_PRIVATE_SYSCALL, and a "ghost syscall private to the kernel" at
+    // MIN_GHOST_SYSCALL.
+    } else if (num_ < MIN_PRIVATE_SYSCALL - 1) {
+      num_ = MIN_PRIVATE_SYSCALL - 1;
+    } else if (num_ <= MAX_PRIVATE_SYSCALL) {
+      if (invalid_only_ && num_ < MAX_PRIVATE_SYSCALL) {
+        num_ = MAX_PRIVATE_SYSCALL;
+      } else {
+        ++num_;
+      }
+    } else if (num_ < MIN_GHOST_SYSCALL - 1) {
+      num_ = MIN_GHOST_SYSCALL - 1;
+    } else if (num_ <= MAX_SYSCALL) {
+      if (invalid_only_ && num_ < MAX_SYSCALL) {
+        num_ = MAX_SYSCALL;
+      } else {
+        ++num_;
+      }
+#endif
+    // BPF programs only ever operate on unsigned quantities. So, that's how
+    // we iterate; we return values from 0..0xFFFFFFFFu. But there are places,
+    // where the kernel might interpret system call numbers as signed
+    // quantities, so the boundaries between signed and unsigned values are
+    // potential problem cases. We want to explicitly return these values from
+    // our iterator.
+    } else if (num_ < 0x7FFFFFFFu) {
+      num_ = 0x7FFFFFFFu;
+    } else if (num_ < 0x80000000u) {
+      num_ = 0x80000000u;
+    } else if (num_ < 0xFFFFFFFFu) {
+      num_ = 0xFFFFFFFFu;
+    }
+  } while (invalid_only_ && IsValid(val));
+
+  done_ |= val == 0xFFFFFFFFu;
+  return val;
+}
+
+bool SyscallIterator::IsValid(uint32_t num) {
+  uint32_t min_syscall = MIN_SYSCALL;
+  if (num >= min_syscall && num <= MAX_PUBLIC_SYSCALL) {
+    return true;
+  }
+  if (IsArmPrivate(num)) {
+    return true;
+  }
+  return false;
+}
+
+bool SyscallIterator::IsArmPrivate(uint32_t num) {
+#if defined(__arm__) && (defined(__thumb__) || defined(__ARM_EABI__))
+  return (num >= MIN_PRIVATE_SYSCALL && num <= MAX_PRIVATE_SYSCALL) ||
+         (num >= MIN_GHOST_SYSCALL && num <= MAX_SYSCALL);
+#else
+  return false;
+#endif
+}
+
+}  // namespace
+