# 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](https://github.com/llvm/llvm-project/blob/328f40f408c218f25695ea42c844e43bef38660b/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](https://github.com/llvm/llvm-project/blob/328f40f408c218f25695ea42c844e43bef38660b/llvm/include/llvm/Support/ErrorOr.h#L162-L164)
`ErrorOr::operator *`) **does** assert on whether or not `HasError` has
been set (see
[ErrorOr.h](https://github.com/llvm/llvm-project/blob/328f40f408c218f25695ea42c844e43bef38660b/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.

This PR is in reference to porting LLDB on AIX.

Link to discussions on llvm discourse and github:

1. https://discourse.llvm.org/t/port-lldb-to-ibm-aix/80640
2. https://github.com/llvm/llvm-project/issues/101657
The complete changes for porting are present in this draft PR:
https://github.com/llvm/llvm-project/pull/102601

- Added changes to make the common host support functions under
`Host/posix` for unix-like system.
Also, created the `unittests/Host/posix/` to test the hostInfo & support
functions for unix-like system.
- Added changes to get the host information for AIX. (GetProcessInfo()) 
(Information like : executable path, arch, process status etc.)

In preparation for removing the `#include "llvm/ADT/StringExtras.h"`
from the header to source file of `llvm/Support/Error.h`, first add in
all the missing includes that were previously included transitively
through this header.

This is fixing all files missed in b0abd4893fa1, 39d8e6e22cd1, and
a11efd49266f.

Differential Revision: https://reviews.llvm.org/D154775

A common reason for LLDB failing to attach to an already-running process on Linux is the Yama security module: https://www.kernel.org/doc/Documentation/security/Yama.txt. This patch adds an explaination and suggested fix when it detects that case happening.

This was previously proposed in D106226, but hasn't been updated in a while. The last request was to put the check in a target-specific location, which is the approach this patch takes. I believe Yama only exists on Linux, so it's put in that package.

This has no end-to-end test because I'm not sure how to set `ptrace_scope` in a test environment -- if there are suggestions on how to do that, I'd be happy to add it. (Also, setting it to `3` is comically irreversible). I tested this locally.

Reviewed By: DavidSpickett, labath

Differential Revision: https://reviews.llvm.org/D144904

This patch replaces (llvm::|)Optional< with std::optional<.  I'll post
a separate patch to clean up the "using" declarations, #include
"llvm/ADT/Optional.h", etc.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

This patch adds #include <optional> to those files containing
llvm::Optional<...> or Optional<...>.

I'll post a separate patch to actually replace llvm::Optional with
std::optional.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

@clayborg found a potential race condition when setting a static
variable. The fix seems simply to use call_once.

All relevant tests pass.

Differential Revision: https://reviews.llvm.org/D131081

As discusses offline with @jj10305, we are updating some naming used throughout the code, specially in the json schema

- traceBuffer -> iptTrace
- core -> cpu

Differential Revision: https://reviews.llvm.org/D127817

This diffs implements per-core tracing on lldb-server. It also includes tests that ensure that tracing can be initiated from the client and that the jLLDBGetState ppacket returns the list of trace buffers per core.

This doesn't include any decoder changes.

Finally, this makes some little changes here and there improving the existing code.

A specific piece of code that can't reliably be tested is when tracing
per core fails due to permissions. In this case we add a
troubleshooting message and this is the manual test:

```
/proc/sys/kernel/perf_event_paranoid set to 1

(lldb) process trace start --per-core-tracing                                         error: perf event syscall failed: Permission denied
 You might need that /proc/sys/kernel/perf_event_paranoid has a value of 0 or -1.
``

Differential Revision: https://reviews.llvm.org/D124858

The StringRef single argument constructor expects a null-terminated
string.  Explicitly pass the size to prevent reading pass the end
of the array.