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.
145 lines
4.3 KiB
C++
145 lines
4.3 KiB
C++
//===-- ProcfsTests.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 "Procfs.h"
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#include "lldb/Host/linux/Support.h"
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#include "lldb/Host/posix/Support.h"
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#include "gmock/gmock.h"
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#include "gtest/gtest.h"
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using namespace lldb_private;
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using namespace process_linux;
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using namespace llvm;
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TEST(Perf, HardcodedLogicalCoreIDs) {
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Expected<std::vector<lldb::cpu_id_t>> cpu_ids =
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GetAvailableLogicalCoreIDs(R"(processor : 13
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vendor_id : GenuineIntel
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cpu family : 6
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model : 85
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model name : Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz
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stepping : 4
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microcode : 0x2000065
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cpu MHz : 2886.370
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cache size : 28160 KB
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physical id : 1
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siblings : 40
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core id : 19
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cpu cores : 20
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apicid : 103
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initial apicid : 103
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fpu : yes
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fpu_exception : yes
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cpuid level : 22
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power management:
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processor : 24
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vendor_id : GenuineIntel
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cpu family : 6
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model : 85
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model name : Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz
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stepping : 4
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microcode : 0x2000065
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cpu MHz : 2768.494
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cache size : 28160 KB
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physical id : 1
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siblings : 40
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core id : 20
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cpu cores : 20
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apicid : 105
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power management:
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processor : 35
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vendor_id : GenuineIntel
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cpu family : 6
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model : 85
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model name : Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz
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stepping : 4
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microcode : 0x2000065
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cpu MHz : 2884.703
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cache size : 28160 KB
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physical id : 1
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siblings : 40
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core id : 24
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cpu cores : 20
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apicid : 113
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processor : 79
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vendor_id : GenuineIntel
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cpu family : 6
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model : 85
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model name : Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz
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stepping : 4
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microcode : 0x2000065
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cpu MHz : 3073.955
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cache size : 28160 KB
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physical id : 1
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siblings : 40
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core id : 28
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cpu cores : 20
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apicid : 121
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power management:
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)");
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ASSERT_TRUE((bool)cpu_ids);
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ASSERT_THAT(*cpu_ids, ::testing::ElementsAre(13, 24, 35, 79));
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}
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TEST(Perf, RealLogicalCoreIDs) {
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// We first check we can read /proc/cpuinfo
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auto buffer_or_error = errorOrToExpected(getProcFile("cpuinfo"));
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if (!buffer_or_error)
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GTEST_SKIP() << toString(buffer_or_error.takeError());
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// At this point we shouldn't fail parsing the core ids
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Expected<ArrayRef<lldb::cpu_id_t>> cpu_ids = GetAvailableLogicalCoreIDs();
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ASSERT_TRUE((bool)cpu_ids);
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ASSERT_GT((int)cpu_ids->size(), 0) << "We must see at least one core";
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}
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TEST(Perf, RealPtraceScopeWhenExist) {
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// We first check we can read /proc/sys/kernel/yama/ptrace_scope
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auto buffer_or_error =
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errorOrToExpected(getProcFile("sys/kernel/yama/ptrace_scope"));
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if (!buffer_or_error)
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GTEST_SKIP() << toString(buffer_or_error.takeError());
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// At this point we shouldn't fail parsing the ptrace_scope value.
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Expected<int> ptrace_scope = GetPtraceScope();
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ASSERT_TRUE((bool)ptrace_scope) << ptrace_scope.takeError();
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ASSERT_GE(*ptrace_scope, 0)
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<< "Sensible values of ptrace_scope are between 0 and 3";
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ASSERT_LE(*ptrace_scope, 3)
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<< "Sensible values of ptrace_scope are between 0 and 3";
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}
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TEST(Perf, RealPtraceScopeWhenNotExist) {
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// We first check we can NOT read /proc/sys/kernel/yama/ptrace_scope
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auto buffer_or_error =
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errorOrToExpected(getProcFile("sys/kernel/yama/ptrace_scope"));
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if (buffer_or_error)
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GTEST_SKIP() << "In order for this test to run, "
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"/proc/sys/kernel/yama/ptrace_scope should not exist";
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consumeError(buffer_or_error.takeError());
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// At this point we should fail parsing the ptrace_scope value.
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Expected<int> ptrace_scope = GetPtraceScope();
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ASSERT_FALSE((bool)ptrace_scope);
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consumeError(ptrace_scope.takeError());
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}
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#ifdef LLVM_ENABLE_THREADING
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TEST(Support, getProcFile_Tid) {
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auto BufferOrError = getProcFile(getpid(), llvm::get_threadid(), "comm");
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ASSERT_TRUE(BufferOrError);
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ASSERT_TRUE(*BufferOrError);
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}
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#endif /*ifdef LLVM_ENABLE_THREADING */
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