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[XRay][compiler-rt] Remove MAP_NORESERVE from XRay allocations 

Summary:
This reverses an earlier decision to allow seg-faulting from the
XRay-allocated memory if it turns out that the system cannot provide
physical memory backing that cannot be swapped in/out on Linux.

This addresses http://llvm.org/PR38588.

Reviewers: eizan

Reviewed By: eizan

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D50831

llvm-svn: 339869
This commit is contained in:
Dean Michael Berris 2018-08-16 12:19:03 +00:00
parent 0e2f0bd48e
commit 560c733815
2 changed files with 3 additions and 27 deletions
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9
compiler-rt/lib/xray/xray_allocator.h
View File

@ -21,14 +21,9 @@
#include "sanitizer_common/sanitizer_mutex.h"
#include "sanitizer_common/sanitizer_posix.h"
#include "xray_utils.h"
#include <sys/mman.h>
#include <cstddef>
#include <cstdint>
#ifndef MAP_NORESERVE
// no-op on NetBSD (at least), unsupported flag on FreeBSD basically because unneeded
#define MAP_NORESERVE 0
#endif
#include <sys/mman.h>
namespace __xray {
@ -69,7 +64,7 @@ private:
if (UNLIKELY(BackingStore == nullptr)) {
BackingStore = reinterpret_cast<void *>(
internal_mmap(NULL, MaxMemory, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, 0, 0));
MAP_PRIVATE | MAP_ANONYMOUS, 0, 0));
if (BackingStore == MAP_FAILED) {
BackingStore = nullptr;
if (Verbosity())

21
compiler-rt/lib/xray/xray_buffer_queue.cc
View File

@ -19,33 +19,14 @@
#include <memory>
#include <sys/mman.h>
#ifndef MAP_NORESERVE
// no-op on NetBSD (at least), unsupported flag on FreeBSD
#define MAP_NORESERVE 0
#endif
using namespace __xray;
using namespace __sanitizer;
template <class T> static T *allocRaw(size_t N) {
// TODO: Report errors?
// We use MAP_NORESERVE on platforms where it's supported to ensure that the
// pages we're allocating for XRay never end up in pages that can be swapped
// in/out. We're doing this because for FDR mode, we want to ensure that
// writes to the buffers stay resident in memory to prevent XRay itself from
// causing swapping/thrashing.
//
// In the case when XRay pages cannot be swapped in/out or there's not enough
// RAM to back these pages, we're willing to cause a segmentation fault
// instead of introducing latency in the measurement. We assume here that
// there are enough pages that are swappable in/out outside of the buffers
// being used by FDR mode (which are bounded and configurable anyway) to allow
// us to keep using always-resident memory.
//
// TODO: Make this configurable?
void *A = reinterpret_cast<void *>(
internal_mmap(NULL, N * sizeof(T), PROT_WRITE | PROT_READ,
MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, -1, 0));
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0));
return (A == MAP_FAILED) ? nullptr : reinterpret_cast<T *>(A);
}