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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>
namespace __xray {
// This is the function to call when we encounter the entry or exit sleds.
std::atomic<void (*)(int32_t, XRayEntryType)> XRayPatchedFunction{nullptr};
} // namespace __xray
extern "C" {
// The following functions have to be defined in assembler, on a per-platform
// basis. See xray_trampoline_*.s files for implementations.
extern void __xray_FunctionEntry();
extern void __xray_FunctionExit();
}
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;
}
std::atomic<bool> XRayPatching{false};
XRayPatchingStatus __xray_patch() {
// FIXME: Make this happen asynchronously. For now just do this sequentially.
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.
}
// Step 1: Compute the function id, as a unique identifier per function in the
// instrumentation map.
__xray::XRaySledMap InstrMap = XRayInstrMap.load(std::memory_order_acquire);
if (InstrMap.Entries == 0)
return XRayPatchingStatus::NOT_INITIALIZED;
int32_t FuncId = 1;
static constexpr uint8_t CallOpCode = 0xe8;
static constexpr uint16_t MovR10Seq = 0xba41;
static constexpr uint8_t JmpOpCode = 0xe9;
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 & ~((2 << 16) - 1));
std::size_t MProtectLen =
(Sled.Address + 12) - reinterpret_cast<uint64_t>(PageAlignedAddr);
if (mprotect(PageAlignedAddr, MProtectLen,
PROT_READ | PROT_WRITE | PROT_EXEC) == -1) {
printf("Failed mprotect: %d\n", errno);
return XRayPatchingStatus::FAILED;
}
static constexpr int64_t MinOffset{std::numeric_limits<int32_t>::min()};
static constexpr int64_t MaxOffset{std::numeric_limits<int32_t>::max()};
if (Sled.Kind == XRayEntryType::ENTRY) {
// Here we do the dance of replacing the following sled:
//
// xray_sled_n:
// jmp +9
// <9 byte nop>
//
// With the following:
//
// mov r10d, <function id>
// call <relative 32bit offset to entry trampoline>
//
// We need to do this in the following order:
//
// 1. Put the function id first, 2 bytes from the start of the sled (just
// after the 2-byte jmp instruction).
// 2. Put the call opcode 6 bytes from the start of the sled.
// 3. Put the relative offset 7 bytes from the start of the sled.
// 4. Do an atomic write over the jmp instruction for the "mov r10d"
// opcode and first operand.
//
// Prerequisite is to compute the relative offset to the
// __xray_FunctionEntry function's address.
int64_t TrampolineOffset =
reinterpret_cast<int64_t>(__xray_FunctionEntry) -
(static_cast<int64_t>(Sled.Address) + 11);
if (TrampolineOffset < MinOffset || TrampolineOffset > MaxOffset) {
// FIXME: Print out an error here.
continue;
}
*reinterpret_cast<uint32_t *>(Sled.Address + 2) = FuncId;
*reinterpret_cast<uint8_t *>(Sled.Address + 6) = CallOpCode;
*reinterpret_cast<uint32_t *>(Sled.Address + 7) = TrampolineOffset;
std::atomic_store_explicit(
reinterpret_cast<std::atomic<uint16_t> *>(Sled.Address), MovR10Seq,
std::memory_order_release);
}
if (Sled.Kind == XRayEntryType::EXIT) {
// Here we do the dance of replacing the following sled:
//
// xray_sled_n:
// ret
// <10 byte nop>
//
// With the following:
//
// mov r10d, <function id>
// jmp <relative 32bit offset to exit trampoline>
//
// 1. Put the function id first, 2 bytes from the start of the sled (just
// after the 1-byte ret instruction).
// 2. Put the jmp opcode 6 bytes from the start of the sled.
// 3. Put the relative offset 7 bytes from the start of the sled.
// 4. Do an atomic write over the jmp instruction for the "mov r10d"
// opcode and first operand.
//
// Prerequisite is to compute the relative offset fo the
// __xray_FunctionExit function's address.
int64_t TrampolineOffset =
reinterpret_cast<int64_t>(__xray_FunctionExit) -
(static_cast<int64_t>(Sled.Address) + 11);
if (TrampolineOffset < MinOffset || TrampolineOffset > MaxOffset) {
// FIXME: Print out an error here.
continue;
}
*reinterpret_cast<uint32_t *>(Sled.Address + 2) = FuncId;
*reinterpret_cast<uint8_t *>(Sled.Address + 6) = JmpOpCode;
*reinterpret_cast<uint32_t *>(Sled.Address + 7) = TrampolineOffset;
std::atomic_store_explicit(
reinterpret_cast<std::atomic<uint16_t> *>(Sled.Address), MovR10Seq,
std::memory_order_release);
}
if (mprotect(PageAlignedAddr, MProtectLen, PROT_READ | PROT_EXEC) == -1) {
printf("Failed mprotect: %d\n", errno);
return XRayPatchingStatus::FAILED;
}
}
XRayPatching.store(false, std::memory_order_release);
return XRayPatchingStatus::NOTIFIED;
}
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