[linux] Use cmake to detect support process_vm_readv (bug #23918)

Summary:
Some old linux versions do not have process_vm_readv function defined. Even older versions do not
have even the __NR_process_vm_readv syscall number. We use cmake to detect these situations and
fallback appropriately: in the first case, we can issue the syscall manually, while it the latter
case, we need to drop fast memory read support completely.

Test Plan: linux test suite passes

Reviewers: ovyalov, Eugene.Zelenko

Subscribers: tberghammer, lldb-commits

Differential Revision: http://reviews.llvm.org/D10727

llvm-svn: 240927

1 files changed, 29 insertions, 0 deletions

diff --git a/lldb/source/Host/linux/LibcGlue.cpp b/lldb/source/Host/linux/LibcGlue.cpp
new file mode 100644
index 00000000000..6e07134971d
--- /dev/null
+++ b/lldb/source/Host/linux/LibcGlue.cpp
@@ -0,0 +1,29 @@
+//===-- LibcGlue.cpp --------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// This file adds functions missing from libc on older versions of linux
+
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <lldb/Host/linux/Uio.h>
+
+#ifndef HAVE_PROCESS_VM_READV // If the syscall wrapper is not available, provide one.
+ssize_t process_vm_readv(::pid_t pid,
+			 const struct iovec *local_iov, unsigned long liovcnt,
+			 const struct iovec *remote_iov, unsigned long riovcnt,
+			 unsigned long flags)
+{
+#ifdef HAVE_NR_PROCESS_VM_READV // If we have the syscall number, we can issue the syscall ourselves.
+    return syscall(__NR_process_vm_readv, pid, local_iov, liovcnt, remote_iov, riovcnt, flags);
+#else // If not, let's pretend the syscall is not present.
+    errno = ENOSYS;
+    return -1;
+#endif
+}
+#endif