[lldb] Fix build on older Linux kernel versions

[kongyi]

Summary

PERF_COUNT_SW_DUMMY is introduced in Linux 3.12.

[jj10306]

Thanks for fixing this!

@wallace perhaps in a followup diff we can add support for these older versions of Linux by just using an arbitrary PERF_COUNT_SW config to get access to the metadata page that contains the TSC conversion parameters? AFAIK the IntelPT code is the only code that uses this logic, so this doesn't really matter since kernel support for IntelPT was added in version 4.2, but if people want to use this logic in another context then this small change of supporting older kernel versions could be nice!

[wallace]

thanks a good point, Jakob. Let's keep it in mind. Maybe we can bootcamp that

[wallace]

@kongyi thanks for fixing this!

lldb/source/Plugins/Process/Linux/Perf.cpp

 
 #include "Plugins/Process/POSIX/ProcessPOSIXLog.h"
 #include "lldb/Host/linux/Support.h"
 
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
 
+#include <linux/version.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
 using namespace lldb_private;
 using namespace process_linux;
 using namespace llvm;
 
 Expected<LinuxPerfZeroTscConversion>
 lldb_private::process_linux::LoadPerfTscConversionParameters() {
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,12,0)
   lldb::pid_t pid = getpid();
   perf_event_attr attr;
   memset(&attr, 0, sizeof(attr));
   attr.size = sizeof(attr);
   attr.type = PERF_TYPE_SOFTWARE;
   attr.config = PERF_COUNT_SW_DUMMY;
 
   Expected<PerfEvent> perf_event = PerfEvent::Init(attr, pid);
if (mmap_metada.cap_user_time && mmap_metada.cap_user_time_zero) {
     auto err_cap =
         !mmap_metada.cap_user_time ? "cap_user_time" : "cap_user_time_zero";
     std::string err_msg =
         llvm::formatv("Can't get TSC to real time conversion values. "
                       "perf_event capability '{0}' not supported.",
                       err_cap);
     return llvm::createStringError(llvm::inconvertibleErrorCode(), err_msg);
   }
+#else
+  std::string err_msg = "PERF_COUNT_SW_DUMMY requires Linux 3.12";
+  return llvm::createStringError(llvm::inconvertibleErrorCode(), err_msg);
+#endif
 }
 
 void resource_handle::MmapDeleter::operator()(void *ptr) {
   if (m_bytes && ptr != nullptr)
     munmap(ptr, m_bytes);
 }
 
 void resource_handle::FileDescriptorDeleter::operator()(long *ptr) {