[llvm] 941188e - [llvm-exegesis] Fix X86LbrCounter destructor to correctly unmap memory and not double-close fd (PR50620)

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2021-06-15T14:24:35+01:00
New Revision: 941188e9653463bc269ecb43e87ec22c63a4a02b

URL: https://github.com/llvm/llvm-project/commit/941188e9653463bc269ecb43e87ec22c63a4a02b
DIFF: https://github.com/llvm/llvm-project/commit/941188e9653463bc269ecb43e87ec22c63a4a02b.diff

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

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

Differential Revision: https://reviews.llvm.org/D104201

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp b/llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp
index 25ec4f8586755..4d2262750e9a3 100644
--- a/llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp
+++ b/llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp
@@ -41,6 +41,10 @@ static constexpr int kLbrEntries = 16;
 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 @@ X86LbrPerfEvent::X86LbrPerfEvent(unsigned SamplingPeriod) {
 
 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 */);