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

[labath]

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.

[ovyalov]

cmake/modules/LLDBConfig.cmake

258 ↗

(On Diff #28442)

Do we need to cast from ssize_t to int?

258 ↗

(On Diff #28442)

Could you pass nullptr for const struct iovec *?

source/Host/linux/LibcGlue.cpp

10 ↗

(On Diff #28442)

s/files/file

[Eugene.Zelenko]

Please define -DHAVE_PROCESS_VM_READV and -DHAVE_NR_PROCESS_VM_READV without values and check them with #ifdef/#ifndef.

I had preprocessor errors with #if ! applied to undefined variable in Uio.h and LibcGlue.cpp.

Build was successful after I changed #if ! to #ifdef.

[Eugene.Zelenko]

Sorry, forgot to set flag in my previous post.

[Eugene.Zelenko]

Just dug in more and this is what I have in DependInfo.cmake files:

"HAVE_NR_PROCESS_VM_READV=1"
"HAVE_PROCESS_VM_READV="

HAVE_PROCESS_VM_READV is defined without value. However, value is completely irrelevant, fact of variable definition should be enough .

[labath]

• Fix preprocessor macro definitions
• Make function check more type-safe

[labath]

• Fix typo

[labath]

My apologies, it seems I misunderstood the operation of check_cxx_source_compiles. Please try it again.

cmake/modules/LLDBConfig.cmake

258 ↗

(On Diff #28442)

done.

source/Host/linux/LibcGlue.cpp

10 ↗

(On Diff #28442)

Done.

[Eugene.Zelenko]

source/Host/linux/LibcGlue.cpp also need to include #include <unistd.h> (for syscall() prototype). Sorry, I didn't catch it yesterday because I incorrectly applied ifndef.

Man page tells to define #define _GNU_SOURCE before #include <unistd.h>.

I'm not sure, but probably macro should start from HAS, not HAVE, since they are about operation system.

[labath]

source/Host/linux/LibcGlue.cpp also need to include #include <unistd.h> (for syscall() prototype). Sorry, I didn't catch it yesterday because I incorrectly applied ifndef.

I've added unistd.h and committed. Let me know if you see any problems.

Man page tells to define #define _GNU_SOURCE before #include <unistd.h>.

This macro is defined (for me at least) on the compiler command line. If this is not the case for you, then we can work it out separately.

I'm not sure, but probably macro should start from HAS, not HAVE, since they are about operation system.

I am testing a feature of the c library (the support in the actual running kernel will be tested at runtime - we need this that way), which seems consistent with all the other HAVE_ macros i've seen.

[Eugene.Zelenko]

Should be OK now.

lldb/trunk/cmake/modules/LLDBConfig.cmake

if(NOT LLDB_REQUIRES_RTTI)
   if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
     set(LLDB_COMPILE_FLAGS "${LLDB_COMPILE_FLAGS} -fno-rtti")
   elseif(MSVC)
     set(LLDB_COMPILE_FLAGS "${LLDB_COMPILE_FLAGS} /GR-")
   endif()
 endif()
 
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${LLDB_COMPILE_FLAGS}")
+
+if (CMAKE_SYSTEM_NAME MATCHES "Linux")
+    # Check for syscall used by lldb-server on linux.
+    # If these are not found, it will fall back to ptrace (slow) for memory reads.
+    check_cxx_source_compiles("
+        #include <sys/uio.h>
+        int main() { process_vm_readv(0, nullptr, 0, nullptr, 0, 0); return 0; }"
+        HAVE_PROCESS_VM_READV)
+
+    if (HAVE_PROCESS_VM_READV)
+        add_definitions(-DHAVE_PROCESS_VM_READV)
+    else()
+        # If we don't have the syscall wrapper function, but we know the syscall number, we can
+        # still issue the syscall manually
+        check_cxx_source_compiles("
+            #include <sys/syscall.h>
+            int main() { return __NR_process_vm_readv; }"
+            HAVE_NR_PROCESS_VM_READV)
+
+        if (HAVE_NR_PROCESS_VM_READV)
+            add_definitions(-DHAVE_NR_PROCESS_VM_READV)
+        endif()
+    endif()
+endif()

lldb/trunk/include/lldb/Host/linux/Uio.h

 //===-- Uio.h ---------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef liblldb_Host_linux_Uio_h_
 #define liblldb_Host_linux_Uio_h_
 
 #include <sys/uio.h>
 
-// Android does not define the process_vm_readv wrapper
-#ifdef __ANDROID_NDK__
+// We shall provide our own implementation of process_vm_readv if it is not present
+#ifndef HAVE_PROCESS_VM_READV
 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);
 #endif
 
 #endif // liblldb_Host_linux_Uio_h_

lldb/trunk/source/Host/CMakeLists.txt

elseif (CMAKE_SYSTEM_NAME MATCHES "Linux")
     if (__ANDROID_NDK__)
       add_host_subdirectory(android
         android/HostInfoAndroid.cpp
         android/LibcGlue.cpp
         android/ProcessLauncherAndroid.cpp
         linux/Host.cpp
         linux/HostInfoLinux.cpp
         linux/HostThreadLinux.cpp
+        linux/LibcGlue.cpp
         linux/ThisThread.cpp
         )
     else()
       add_host_subdirectory(linux
         linux/Host.cpp
         linux/HostInfoLinux.cpp
         linux/HostThreadLinux.cpp
+        linux/LibcGlue.cpp
         linux/ThisThread.cpp
         )
     endif()
   elseif (CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
     add_host_subdirectory(freebsd
       freebsd/Host.cpp
       freebsd/HostInfoFreeBSD.cpp
       freebsd/HostThreadFreeBSD.cpp
       freebsd/ThisThread.cpp
       )
   endif()
 endif()
 
 add_lldb_library(lldbHost ${HOST_SOURCES})

lldb/trunk/source/Host/android/LibcGlue.cpp

 //===-- 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 files adds functions missing from libc on earlier versions of Android
 
 #include <android/api-level.h>
 
 #include <sys/syscall.h>
-#include <lldb/Host/linux/Uio.h>
 
 #if __ANDROID_API__ < 21
 
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <signal.h>
 

 }
 
 int posix_openpt(int flags)
 {
     return open("/dev/ptmx", flags);
 }
 
 #endif
-
-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)
-{
-    return syscall(__NR_process_vm_readv, pid, local_iov, liovcnt, remote_iov, riovcnt, flags);
-}

lldb/trunk/source/Host/linux/LibcGlue.cpp

+//===-- 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