[PATCH] D104201: [llvm-exegesis] Fix X86LbrCounter destructor to correctly unmap memory and not double-close fd (PR50620)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: gchatelet, courbet, lebedev.ri.
Herald added subscribers: mstojanovic, pengfei.
RKSimon requested review of this revision.
Herald added a project: LLVM.

As was reported on PR50620, the X86LbrCounter destructor was double-closing the filedescriptor and not unmapping the buffer.

NOTE: I haven't built this on a pfm enabled linux box to check that it actually works, but hopefully the premise is sound - if someone can check it sooner that's great, otherwise it will happen next week when I have access again.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D104201

Files:
  llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp


Index: llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp
===================================================================
--- llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp
+++ llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp
@@ -41,6 +41,10 @@
 static constexpr size_t kBufferPages = 8;
 static const size_t kDataBufferSize = kBufferPages * getpagesize();
 
+// First page is reserved for perf_event_mmap_page. Data buffer starts on
+// the next page, so we allocate one more page.
+static const size_t kMappedBufferSize = (kBufferPages + 1) * getpagesize();
+
 // Waits for the LBR perf events.
 static int pollLbrPerfEvent(const int FileDescriptor) {
   struct pollfd PollFd;
@@ -137,15 +141,16 @@
 
 X86LbrCounter::X86LbrCounter(pfm::PerfEvent &&NewEvent)
     : Counter(std::move(NewEvent)) {
-  // First page is reserved for perf_event_mmap_page. Data buffer starts on
-  // the next page, so we allocate one more page.
-  MMappedBuffer = mmap(nullptr, (kBufferPages + 1) * getpagesize(),
-                       PROT_READ | PROT_WRITE, MAP_SHARED, FileDescriptor, 0);
+  MMappedBuffer = mmap(nullptr, kMappedBufferSize, PROT_READ | PROT_WRITE,
+                       MAP_SHARED, FileDescriptor, 0);
   if (MMappedBuffer == MAP_FAILED)
     llvm::errs() << "Failed to mmap buffer.";
 }
 
-X86LbrCounter::~X86LbrCounter() { close(FileDescriptor); }
+X86LbrCounter::~X86LbrCounter() {
+  if (0 != munmap(MMappedBuffer, kMappedBufferSize))
+    llvm::errs() << "Failed to munmap buffer.";
+}
 
 void X86LbrCounter::start() {
   ioctl(FileDescriptor, PERF_EVENT_IOC_REFRESH, 1024 /* kMaxPollsPerFd */);


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