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187 lines
5.7 KiB
187 lines
5.7 KiB
4 months ago
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//===-- SingleStepCheck.cpp -----------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "SingleStepCheck.h"
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#include <sched.h>
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#include <signal.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#include "NativeProcessLinux.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Errno.h"
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#include "Plugins/Process/POSIX/ProcessPOSIXLog.h"
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#include "lldb/Host/linux/Ptrace.h"
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#include "lldb/Utility/Status.h"
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using namespace lldb;
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using namespace lldb_private;
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using namespace lldb_private::process_linux;
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#if defined(__arm64__) || defined(__aarch64__)
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namespace {
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void LLVM_ATTRIBUTE_NORETURN Child() {
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if (ptrace(PTRACE_TRACEME, 0, nullptr, nullptr) == -1)
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_exit(1);
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// We just do an endless loop SIGSTOPPING ourselves until killed. The tracer
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// will fiddle with our cpu affinities and monitor the behaviour.
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for (;;) {
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raise(SIGSTOP);
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// Generate a bunch of instructions here, so that a single-step does not
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// land in the raise() accidentally. If single-stepping works, we will be
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// spinning in this loop. If it doesn't, we'll land in the raise() call
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// above.
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for (volatile unsigned i = 0; i < CPU_SETSIZE; ++i)
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;
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}
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}
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struct ChildDeleter {
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::pid_t pid;
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~ChildDeleter() {
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int status;
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// Kill the child.
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kill(pid, SIGKILL);
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// Pick up the remains.
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llvm::sys::RetryAfterSignal(-1, waitpid, pid, &status, __WALL);
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}
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};
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bool WorkaroundNeeded() {
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// We shall spawn a child, and use it to verify the debug capabilities of the
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// cpu. We shall iterate through the cpus, bind the child to each one in
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// turn, and verify that single-stepping works on that cpu. A workaround is
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// needed if we find at least one broken cpu.
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Log *log = ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_THREAD);
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::pid_t child_pid = fork();
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if (child_pid == -1) {
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LLDB_LOG(log, "failed to fork(): {0}", Status(errno, eErrorTypePOSIX));
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return false;
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}
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if (child_pid == 0)
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Child();
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ChildDeleter child_deleter{child_pid};
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cpu_set_t available_cpus;
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if (sched_getaffinity(child_pid, sizeof available_cpus, &available_cpus) ==
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-1) {
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LLDB_LOG(log, "failed to get available cpus: {0}",
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Status(errno, eErrorTypePOSIX));
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return false;
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}
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int status;
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::pid_t wpid = llvm::sys::RetryAfterSignal(-1, waitpid,
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child_pid, &status, __WALL);
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if (wpid != child_pid || !WIFSTOPPED(status)) {
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LLDB_LOG(log, "waitpid() failed (status = {0:x}): {1}", status,
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Status(errno, eErrorTypePOSIX));
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return false;
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}
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unsigned cpu;
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for (cpu = 0; cpu < CPU_SETSIZE; ++cpu) {
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if (!CPU_ISSET(cpu, &available_cpus))
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continue;
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cpu_set_t cpus;
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CPU_ZERO(&cpus);
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CPU_SET(cpu, &cpus);
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if (sched_setaffinity(child_pid, sizeof cpus, &cpus) == -1) {
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LLDB_LOG(log, "failed to switch to cpu {0}: {1}", cpu,
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Status(errno, eErrorTypePOSIX));
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continue;
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}
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int status;
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Status error =
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NativeProcessLinux::PtraceWrapper(PTRACE_SINGLESTEP, child_pid);
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if (error.Fail()) {
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LLDB_LOG(log, "single step failed: {0}", error);
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break;
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}
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wpid = llvm::sys::RetryAfterSignal(-1, waitpid,
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child_pid, &status, __WALL);
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if (wpid != child_pid || !WIFSTOPPED(status)) {
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LLDB_LOG(log, "waitpid() failed (status = {0:x}): {1}", status,
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Status(errno, eErrorTypePOSIX));
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break;
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}
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if (WSTOPSIG(status) != SIGTRAP) {
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LLDB_LOG(log, "single stepping on cpu {0} failed with status {1:x}", cpu,
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status);
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break;
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}
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}
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// cpu is either the index of the first broken cpu, or CPU_SETSIZE.
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if (cpu == 0) {
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LLDB_LOG(log,
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"SINGLE STEPPING ON FIRST CPU IS NOT WORKING. DEBUGGING "
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"LIKELY TO BE UNRELIABLE.");
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// No point in trying to fiddle with the affinities, just give it our best
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// shot and see how it goes.
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return false;
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}
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return cpu != CPU_SETSIZE;
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}
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} // end anonymous namespace
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std::unique_ptr<SingleStepWorkaround> SingleStepWorkaround::Get(::pid_t tid) {
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Log *log = ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_THREAD);
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static bool workaround_needed = WorkaroundNeeded();
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if (!workaround_needed) {
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LLDB_LOG(log, "workaround for thread {0} not needed", tid);
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return nullptr;
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}
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cpu_set_t original_set;
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if (sched_getaffinity(tid, sizeof original_set, &original_set) != 0) {
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// This should really not fail. But, just in case...
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LLDB_LOG(log, "Unable to get cpu affinity for thread {0}: {1}", tid,
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Status(errno, eErrorTypePOSIX));
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return nullptr;
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}
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cpu_set_t set;
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CPU_ZERO(&set);
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CPU_SET(0, &set);
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if (sched_setaffinity(tid, sizeof set, &set) != 0) {
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// This may fail in very locked down systems, if the thread is not allowed
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// to run on cpu 0. If that happens, only thing we can do is it log it and
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// continue...
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LLDB_LOG(log, "Unable to set cpu affinity for thread {0}: {1}", tid,
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Status(errno, eErrorTypePOSIX));
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}
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LLDB_LOG(log, "workaround for thread {0} prepared", tid);
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return std::make_unique<SingleStepWorkaround>(tid, original_set);
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}
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SingleStepWorkaround::~SingleStepWorkaround() {
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Log *log = ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_THREAD);
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LLDB_LOG(log, "Removing workaround");
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if (sched_setaffinity(m_tid, sizeof m_original_set, &m_original_set) != 0) {
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LLDB_LOG(log, "Unable to reset cpu affinity for thread {0}: {1}", m_tid,
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Status(errno, eErrorTypePOSIX));
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}
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}
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#endif
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