8e8da88d46
# Symptom We have seen SIGSEGV like this: ``` * thread #1, name = 'lldb-server', stop reason = SIGSEGV frame #0: 0x00007f39e529c993 libc.so.6`__pthread_kill_internal(signo=11, threadid=<unavailable>) at pthread_kill.c:46:37 ... * frame #5: 0x000056027c94fe48 lldb-server`lldb_private::process_linux::GetPtraceScope() + 72 frame #6: 0x000056027c92f94f lldb-server`lldb_private::process_linux::NativeProcessLinux::Attach(int) + 1087 ... ``` See [full stack trace](https://pastebin.com/X0d6QhYj). This happens on Linux where LLDB doesn't have access to `/proc/sys/kernel/yama/ptrace_scope`. A similar error (an unchecked `Error`) can be reproduced by running the newly added unit test without the fix. See the "Test" section below. # Root cause `GetPtraceScope()` ([code](328f40f408/lldb/source/Plugins/Process/Linux/Procfs.cpp (L77))) has the following `if` statement: ``` llvm::Expected<int> lldb_private::process_linux::GetPtraceScope() { ErrorOr<std::unique_ptr<MemoryBuffer>> ptrace_scope_file = getProcFile("sys/kernel/yama/ptrace_scope"); if (!*ptrace_scope_file) return errorCodeToError(ptrace_scope_file.getError()); ... } ``` The intention of the `if` statement is to check whether the `ptrace_scope_file` is an `Error` or not, and return the error if it is. However, the `operator*` of `ErrorOr` returns the value that is stored (which is a `std::unique_ptr<MemoryBuffer>`), so what the `if` condition actually do is to check if the unique pointer is non-null. Note that the method `ErrorOr::getStorage()` ([called by](328f40f408/llvm/include/llvm/Support/ErrorOr.h (L162-L164)) `ErrorOr::operator *`) **does** assert on whether or not `HasError` has been set (see [ErrorOr.h](328f40f408/llvm/include/llvm/Support/ErrorOr.h (L235-L243))). However, it seems this wasn't executed, probably because the LLDB was a release build. # Fix The fix is simply remove the `*` in the said `if` statement.
88 lines
3.0 KiB
C++
88 lines
3.0 KiB
C++
//===-- Procfs.cpp --------------------------------------------------------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "Procfs.h"
|
|
#include "lldb/Host/posix/Support.h"
|
|
#include "llvm/ADT/StringExtras.h"
|
|
#include "llvm/Support/Error.h"
|
|
#include "llvm/Support/MemoryBuffer.h"
|
|
#include "llvm/Support/Threading.h"
|
|
#include <optional>
|
|
|
|
using namespace lldb;
|
|
using namespace lldb_private;
|
|
using namespace process_linux;
|
|
using namespace llvm;
|
|
|
|
Expected<ArrayRef<uint8_t>> lldb_private::process_linux::GetProcfsCpuInfo() {
|
|
static ErrorOr<std::unique_ptr<MemoryBuffer>> cpu_info_or_err =
|
|
getProcFile("cpuinfo");
|
|
|
|
if (!*cpu_info_or_err)
|
|
cpu_info_or_err.getError();
|
|
|
|
MemoryBuffer &buffer = **cpu_info_or_err;
|
|
return arrayRefFromStringRef(buffer.getBuffer());
|
|
}
|
|
|
|
Expected<std::vector<cpu_id_t>>
|
|
lldb_private::process_linux::GetAvailableLogicalCoreIDs(StringRef cpuinfo) {
|
|
SmallVector<StringRef, 8> lines;
|
|
cpuinfo.split(lines, "\n", /*MaxSplit=*/-1, /*KeepEmpty=*/false);
|
|
std::vector<cpu_id_t> logical_cores;
|
|
|
|
for (StringRef line : lines) {
|
|
std::pair<StringRef, StringRef> key_value = line.split(':');
|
|
auto key = key_value.first.trim();
|
|
auto val = key_value.second.trim();
|
|
if (key == "processor") {
|
|
cpu_id_t processor;
|
|
if (val.getAsInteger(10, processor))
|
|
return createStringError(
|
|
inconvertibleErrorCode(),
|
|
"Failed parsing the /proc/cpuinfo line entry: %s", line.data());
|
|
logical_cores.push_back(processor);
|
|
}
|
|
}
|
|
return logical_cores;
|
|
}
|
|
|
|
llvm::Expected<llvm::ArrayRef<cpu_id_t>>
|
|
lldb_private::process_linux::GetAvailableLogicalCoreIDs() {
|
|
static std::optional<std::vector<cpu_id_t>> logical_cores_ids;
|
|
if (!logical_cores_ids) {
|
|
// We find the actual list of core ids by parsing /proc/cpuinfo
|
|
Expected<ArrayRef<uint8_t>> cpuinfo = GetProcfsCpuInfo();
|
|
if (!cpuinfo)
|
|
return cpuinfo.takeError();
|
|
|
|
Expected<std::vector<cpu_id_t>> cpu_ids = GetAvailableLogicalCoreIDs(
|
|
StringRef(reinterpret_cast<const char *>(cpuinfo->data())));
|
|
if (!cpu_ids)
|
|
return cpu_ids.takeError();
|
|
|
|
logical_cores_ids.emplace(std::move(*cpu_ids));
|
|
}
|
|
return *logical_cores_ids;
|
|
}
|
|
|
|
llvm::Expected<int> lldb_private::process_linux::GetPtraceScope() {
|
|
ErrorOr<std::unique_ptr<MemoryBuffer>> ptrace_scope_file =
|
|
getProcFile("sys/kernel/yama/ptrace_scope");
|
|
if (!ptrace_scope_file)
|
|
return errorCodeToError(ptrace_scope_file.getError());
|
|
// The contents should be something like "1\n". Trim it so we get "1".
|
|
StringRef buffer = (*ptrace_scope_file)->getBuffer().trim();
|
|
int ptrace_scope_value;
|
|
if (buffer.getAsInteger(10, ptrace_scope_value)) {
|
|
return createStringError(inconvertibleErrorCode(),
|
|
"Invalid ptrace_scope value: '%s'", buffer.data());
|
|
}
|
|
return ptrace_scope_value;
|
|
}
|