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//===-- xray_interface.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 is a part of XRay, a dynamic runtime instrumentation system.
//
// Implementation of the API functions.
//
//===----------------------------------------------------------------------===//
#include "xray_interface_internal.h"
#include <atomic>
#include <cstdint>
#include <cstdio>
#include <errno.h>
#include <limits>
#include <sys/mman.h>
#include "sanitizer_common/sanitizer_common.h"
namespace __xray {
#if defined(__x86_64__)
// FIXME: The actual length is 11 bytes. Why was length 12 passed to mprotect()
// ?
static const int16_t cSledLength = 12;
#elif defined(__arm__)
static const int16_t cSledLength = 28;
#else
#error "Unsupported CPU Architecture"
#endif /* CPU architecture */
// This is the function to call when we encounter the entry or exit sleds.
std::atomic<void (*)(int32_t, XRayEntryType)> XRayPatchedFunction{nullptr};
// MProtectHelper is an RAII wrapper for calls to mprotect(...) that will undo
// any successful mprotect(...) changes. This is used to make a page writeable
// and executable, and upon destruction if it was successful in doing so returns
// the page into a read-only and executable page.
//
// This is only used specifically for runtime-patching of the XRay
// instrumentation points. This assumes that the executable pages are originally
// read-and-execute only.
class MProtectHelper {
void *PageAlignedAddr;
std::size_t MProtectLen;
bool MustCleanup;
public:
explicit MProtectHelper(void *PageAlignedAddr, std::size_t MProtectLen)
: PageAlignedAddr(PageAlignedAddr), MProtectLen(MProtectLen),
MustCleanup(false) {}
int MakeWriteable() {
auto R = mprotect(PageAlignedAddr, MProtectLen,
PROT_READ | PROT_WRITE | PROT_EXEC);
if (R != -1)
MustCleanup = true;
return R;
}
~MProtectHelper() {
if (MustCleanup) {
mprotect(PageAlignedAddr, MProtectLen, PROT_READ | PROT_EXEC);
}
}
};
} // namespace __xray
extern std::atomic<bool> XRayInitialized;
extern std::atomic<__xray::XRaySledMap> XRayInstrMap;
int __xray_set_handler(void (*entry)(int32_t, XRayEntryType)) {
if (XRayInitialized.load(std::memory_order_acquire)) {
__xray::XRayPatchedFunction.store(entry, std::memory_order_release);
return 1;
}
return 0;
}
int __xray_remove_handler() { return __xray_set_handler(nullptr); }
std::atomic<bool> XRayPatching{false};
using namespace __xray;
// FIXME: Figure out whether we can move this class to sanitizer_common instead
// as a generic "scope guard".
template <class Function> class CleanupInvoker {
Function Fn;
public:
explicit CleanupInvoker(Function Fn) : Fn(Fn) {}
CleanupInvoker(const CleanupInvoker &) = default;
CleanupInvoker(CleanupInvoker &&) = default;
CleanupInvoker &operator=(const CleanupInvoker &) = delete;
CleanupInvoker &operator=(CleanupInvoker &&) = delete;
~CleanupInvoker() { Fn(); }
};
template <class Function> CleanupInvoker<Function> ScopeCleanup(Function Fn) {
return CleanupInvoker<Function>{Fn};
}
// ControlPatching implements the common internals of the patching/unpatching
// implementation. |Enable| defines whether we're enabling or disabling the
// runtime XRay instrumentation.
XRayPatchingStatus ControlPatching(bool Enable) {
if (!XRayInitialized.load(std::memory_order_acquire))
return XRayPatchingStatus::NOT_INITIALIZED; // Not initialized.
static bool NotPatching = false;
if (!XRayPatching.compare_exchange_strong(NotPatching, true,
std::memory_order_acq_rel,
std::memory_order_acquire)) {
return XRayPatchingStatus::ONGOING; // Already patching.
}
bool PatchingSuccess = false;
auto XRayPatchingStatusResetter = ScopeCleanup([&PatchingSuccess] {
if (!PatchingSuccess) {
XRayPatching.store(false, std::memory_order_release);
}
});
// Step 1: Compute the function id, as a unique identifier per function in the
// instrumentation map.
XRaySledMap InstrMap = XRayInstrMap.load(std::memory_order_acquire);
if (InstrMap.Entries == 0)
return XRayPatchingStatus::NOT_INITIALIZED;
const uint64_t PageSize = GetPageSizeCached();
if ((PageSize == 0) || ((PageSize & (PageSize - 1)) != 0)) {
Report("System page size is not a power of two: %lld", PageSize);
return XRayPatchingStatus::FAILED;
}
uint32_t FuncId = 1;
uint64_t CurFun = 0;
for (std::size_t I = 0; I < InstrMap.Entries; I++) {
auto Sled = InstrMap.Sleds[I];
auto F = Sled.Function;
if (CurFun == 0)
CurFun = F;
if (F != CurFun) {
++FuncId;
CurFun = F;
}
// While we're here, we should patch the nop sled. To do that we mprotect
// the page containing the function to be writeable.
void *PageAlignedAddr =
reinterpret_cast<void *>(Sled.Address & ~(PageSize - 1));
std::size_t MProtectLen = (Sled.Address + cSledLength) -
reinterpret_cast<uint64_t>(PageAlignedAddr);
MProtectHelper Protector(PageAlignedAddr, MProtectLen);
if (Protector.MakeWriteable() == -1) {
printf("Failed mprotect: %d\n", errno);
return XRayPatchingStatus::FAILED;
}
bool Success = false;
switch (Sled.Kind) {
case XRayEntryType::ENTRY:
Success = patchFunctionEntry(Enable, FuncId, Sled);
break;
case XRayEntryType::EXIT:
Success = patchFunctionExit(Enable, FuncId, Sled);
break;
default:
Report("Unsupported sled kind: %d", int(Sled.Kind));
continue;
}
(void)Success;
}
XRayPatching.store(false, std::memory_order_release);
PatchingSuccess = true;
return XRayPatchingStatus::SUCCESS;
}
XRayPatchingStatus __xray_patch() { return ControlPatching(true); }
XRayPatchingStatus __xray_unpatch() { return ControlPatching(false); }
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