This functionality is subsumed by DataBufferLLVM, which is
also more efficient since it will try to mmap. However, we
don't yet support mmaping writable private sections, and in
some cases we were using ReadFileContents and then modifying
the buffer. To address that I've added a flag to the
DataBufferLLVM methods that allow you to map privately, which
disables the mmaping path entirely. Eventually we should teach
DataBufferLLVM to use mmap with writable private, but that is
orthogonal to this effort.
Differential Revision: https://reviews.llvm.org/D30622
llvm-svn: 297095
All references to Host and Core have been removed, so this
class can now safely be lowered into Utility.
Differential Revision: https://reviews.llvm.org/D30559
llvm-svn: 296909
Instead just rely on LLDB_LOG().
This is part of an effort to sort out dependency hell in LLDB.
Error is in Utility, but Log is in Core. Core can depend on
Utility, but not vice versa. So this patch moves the knowledge
about how to log Errors from the Error class to the Log file.
Differential Revision: https://reviews.llvm.org/D29514
llvm-svn: 294210
This moves the following classes from Core -> Utility.
ConstString
Error
RegularExpression
Stream
StreamString
The goal here is to get lldbUtility into a state where it has
no dependendencies except on itself and LLVM, so it can be the
starting point at which to start untangling LLDB's dependencies.
These are all low level and very widely used classes, and
previously lldbUtility had dependencies up to lldbCore in order
to use these classes. So moving then down to lldbUtility makes
sense from both the short term and long term perspective in
solving this problem.
Differential Revision: https://reviews.llvm.org/D29427
llvm-svn: 293941
Summary:
Use ProcessLauncherPosixFork in Linux and NetBSD.
Changes to ProcessLauncherLinux:
- Limit personality.h and ASLR code to Linux.
- Reuse portable ptrace(2) PT_TRACE_ME operation available on Linux and BSDs.
- Limit ETXTBSY error path from execve(2) to Linux.
- In LaunchProcess declaration change virtual to override.
This code should be readily available for FreeBSD.
Sponsored by <The NetBSD Foundation>
Reviewers: joerg, clayborg, labath, emaste
Reviewed By: labath
Subscribers: danalbert, srhines, mgorny, #lldb
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D29347
llvm-svn: 293768
Summary:
To retrieve the native thread ID there must be called _lwp_self().
Sponsored by <The NetBSD Foundation>
Reviewers: joerg, clayborg, emaste, labath
Reviewed By: joerg, clayborg, labath
Subscribers: #lldb
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D29264
llvm-svn: 293625
LLDB needs some minor changes to adopt PrettyStackTrace after https://reviews.llvm.org/D27683.
We remove our own SetCrashDescription() function and use LLVM-provided RAII objects instead.
We also make sure LLDB doesn't define __crashtracer_info__ which would collide with LLVM's definition.
Differential Revision: https://reviews.llvm.org/D27735
llvm-svn: 289711
Summary:
This replaces all the uses of the __ANDROID_NDK__ define with __ANDROID__. This
is a preparatory step to remove our custom android toolchain file and rely on
the standard android NDK one instead, which does not provide this define.
Instead I rely, on __ANDROID__, which is set by the compiler.
I haven't yet removed the cmake variable with the same name, as we will need to
do something completely different there -- NDK toolchain defines
CMAKE_SYSTEM_NAME to Android, while our current one pretends it's linux.
Reviewers: tberghammer, zturner
Subscribers: danalbert, srhines, mgorny, lldb-commits
Differential Revision: https://reviews.llvm.org/D27305
llvm-svn: 288494
*** to conform to clang-format’s LLVM style. This kind of mass change has
*** two obvious implications:
Firstly, merging this particular commit into a downstream fork may be a huge
effort. Alternatively, it may be worth merging all changes up to this commit,
performing the same reformatting operation locally, and then discarding the
merge for this particular commit. The commands used to accomplish this
reformatting were as follows (with current working directory as the root of
the repository):
find . \( -iname "*.c" -or -iname "*.cpp" -or -iname "*.h" -or -iname "*.mm" \) -exec clang-format -i {} +
find . -iname "*.py" -exec autopep8 --in-place --aggressive --aggressive {} + ;
The version of clang-format used was 3.9.0, and autopep8 was 1.2.4.
Secondly, “blame” style tools will generally point to this commit instead of
a meaningful prior commit. There are alternatives available that will attempt
to look through this change and find the appropriate prior commit. YMMV.
llvm-svn: 280751
This finally removes the use of the Mutex and Condition classes. This is an
intricate patch as the Mutex and Condition classes were tied together.
Furthermore, many places had slightly differing uses of time values. Convert
timeout values to relative everywhere to permit the use of
std::chrono::duration, which is required for the use of
std::condition_variable's timeout. Adjust all Condition and related Mutex
classes over to std::{,recursive_}mutex and std::condition_variable.
This change primarily comes at the cost of breaking the TracingMutex which was
based around the Mutex class. It would be possible to write a wrapper to
provide similar functionality, but that is beyond the scope of this change.
llvm-svn: 277011
Summary:
We've had two copies of code for launching processes:
- one in NativeProcessLinux, used for launching debugged processes
- one in ProcessLauncherAndroid, used on android for launching all other kinds of processes
These have over time acquired support for various launch options, but neither supported all of
them. I now replace them with a single implementation ProcessLauncherLinux, which supports all
the options the individual versions supported and set it to be used to launch all processes on
linux.
This also works around the ETXTBSY issue on android when the process is started from the platform
instance, as that used to go through the version which did not contain the workaround.
Reviewers: tberghammer
Subscribers: tberghammer, danalbert, srhines, lldb-commits
Differential Revision: https://reviews.llvm.org/D22457
llvm-svn: 276288
Summary:
This replaces the C-style "void *" baton of the child process monitoring functions with a more
C++-like API taking a std::function. The motivation for this was that it was very difficult to
handle the ownership of the object passed into the callback function -- each caller ended up
implementing his own way of doing it, some doing it better than others. With the new API, one can
just pass a smart pointer into the callback and all of the lifetime management will be handled
automatically.
This has enabled me to simplify the rather complicated handshake in Host::RunShellCommand. I have
left handling of MonitorDebugServerProcess (my original motivation for this change) to a separate
commit to reduce the scope of this change.
Reviewers: clayborg, zturner, emaste, krytarowski
Subscribers: lldb-commits
Differential Revision: http://reviews.llvm.org/D20106
llvm-svn: 269205
There were a number of const qualifiers being cast away which caused warnings.
This cluttered the output hiding real errors. Silence them by explicit casting.
NFC.
llvm-svn: 250662
Summary:
- Consolidate Unix signals selection in UnixSignals.
- Make Unix signals available from platform.
- Add jSignalsInfo packet to retrieve Unix signals from remote platform.
- Get a copy of the platform signal for each remote process.
- Update SB API for signals.
- Update signal utility in test suite.
Reviewers: ovyalov, clayborg
Subscribers: chaoren, jingham, labath, emaste, tberghammer, lldb-commits
Differential Revision: http://reviews.llvm.org/D11094
llvm-svn: 242101
Summary:
This should solve the issue of sending denormalized paths over gdb-remote
if we stick to GetPath(false) in GDBRemoteCommunicationClient, and let the
server handle any denormalization.
Reviewers: ovyalov, zturner, vharron, clayborg
Reviewed By: clayborg
Subscribers: tberghammer, emaste, lldb-commits
Differential Revision: http://reviews.llvm.org/D9728
llvm-svn: 238604
Summary:
Fixes http://reviews.llvm.org/D8511
The original method of using dladdr() could return the incorrect relative
path if not dynamically linked against liblldb and the working directory
has changed. This is not a problem when built with python, since
ScriptInterpreterPython::InitializePrivate calls
HostInfo::GetLLDBPath(ePathTypeLLDBShlibDir, ...) and caches the
correct path before any changes to the working directory.
The /proc/self/exe approach fails if run using Python, but works for all other
cases (including for android, which doesn't have dladdr()).
So if we combine the two, we should reasonably cover all corner cases.
Reviewers: vharron, ovyalov, clayborg
Reviewed By: ovyalov, clayborg
Subscribers: lldb-commits
Differential Revision: http://reviews.llvm.org/D8570
llvm-svn: 233129
This creates a new top-level folder called Initialization which
is intended to hold code specific to LLDB system initialization.
Currently this holds the Initialize() and Terminate() functions,
as well as the fatal error handler.
This provides a means to break the massive dependency cycle which
is caused by the fact that Debugger depends on Initialize and
Terminate which then depends on the entire LLDB project. With
this structure, it will be possible for applications to invoke
lldb_private::Initialize() directly, and have that invoke
Debugger::Initialize.
llvm-svn: 232768
This CL change the logic used to terminate the monitor thread of
NativeProcessLinux to use a signal instead of pthread_cancel as
pthread_cancel is not supported on android.
Differential revision: http://reviews.llvm.org/D8205
llvm-svn: 232155
This removes Host::Backtrace from the codebase, and changes all
call sites to use llvm::sys::PrintStackTrace(). This makes the
functionality available for all platforms, and even for platforms
which currently had a supported implementation of Host::Backtrace,
this patch should enable richer information in stack traces, such
as file and line number information, as well as giving it the
ability to unwind through inlined functions.
llvm-svn: 231511
* Create new platform plugin for lldb
* Create HostInfo class for android
* Create ProcessLauncher for android
Differential Revision: http://reviews.llvm.org/D7584
llvm-svn: 228943
Summary:
I don't know if there is a better way for the change in source/Host/freebsd/ThisThread.cpp
Reviewers: emaste
Subscribers: hansw, emaste, lldb-commits
Differential Revision: http://reviews.llvm.org/D7441
llvm-svn: 228710
lldb::pid_t
Host::LaunchApplication (const FileSpec &app_file_spec);
This had use of a function FSPathMakeRef(const UInt8*, FSRef *, ...) that was deprecated in 10.8.
Removing this fucntion since it wasn't used and was causing warnings.
llvm-svn: 226608
This is a resubmit of r223548, which was reverted due to breaking
tests on Linux and Mac.
This resubmit fixes the reason for the revert by adding back some
accidentally removed code which appends -c to the command line
when running /bin/sh.
This resubmit also differs from the original patch in that it sets
the architecture on the ProcessLaunchInfo. A follow-up patch will
refactor this to separate the logic for different platforms.
Differential Revision: http://reviews.llvm.org/D6553
Reviewed By: Greg Clayton
llvm-svn: 223695
(e.g. breakpoints, stop-hooks) before we have any targets - for instance in
your ~/.lldbinit file. These will then get copied over to any new targets
that get created. So far, you can only make stop-hooks.
Breakpoints will have to learn to move themselves from target to target for
us to get them from no-target to new-target.
We should also make a command & SB API way to prime this ur-target.
llvm-svn: 222600
After the recent migration of code out of Host.cpp, many
unnecessary headers were still being included. This prunes the
include list down to only what is still necessary.
llvm-svn: 219814
This implements Host::LaunchProcess for windows, and in doing so
does some minor refactor to move towards a more modular process
launching design.
The original motivation for this is that launching processes on
windows needs some very windows specific code, which would live
most appropriately in source/Host/windows somewhere. However,
there is already some common code that all platforms use when
launching a process before delegating to the platform specific
stuff, which lives in source/Host/common/Host.cpp which would
be nice to reuse without duplicating.
This commonality has been abstracted into MonitoringProcessLauncher,
a class which abstracts out the notion of launching a process using
an arbitrary algorithm, and then monitoring it for state changes.
The windows specific launching code lives in ProcessLauncherWindows,
and the posix specific launching code lives in ProcessLauncherPosix.
When launching a process MonitoringProcessLauncher is created, and
then an appropriate delegate launcher is created and given to the
MonitoringProcessLauncher.
Reviewed by: Greg Clayton
Differential Revision: http://reviews.llvm.org/D5781
llvm-svn: 219731
See http://reviews.llvm.org/D5495 for more details.
These are changes that are part of an effort to support building llgs, within the AOSP source tree, using the Android.mk
build system, when using the llvm/clang/lldb git repos from AOSP replaced with the experimental ones currently in
github.com/tfiala/aosp-{llvm,clang,lldb,compiler-rt}.
llvm-svn: 218568
Changes include:
- fix it so you can select the "host" platform using "platform select host"
- change all callbacks that create platforms to returns shared pointers
- fix TestImageListMultiArchitecture.py to restore the "host" platform by running "platform select host"
- Add a new "PlatformSP Platform::Find(const ConstString &name)" method to get a cached platform
- cache platforms that are created and re-use them instead of always creating a new one
llvm-svn: 218145
This patch moves creates a thread abstraction that represents a
thread running inside the LLDB process. This is a replacement for
otherwise using lldb::thread_t, and provides a platform agnostic
interface to managing these threads.
Differential Revision: http://reviews.llvm.org/D5198
Reviewed by: Jim Ingham
llvm-svn: 217460
See http://reviews.llvm.org/D5108 for details.
This change does the following:
* eliminates the Process::GetUnixSignals() virtual method and replaces with a fixed getter.
* replaces the Process UnixSignals storage with a shared pointer.
* adds a Process constructor variant that can be passed the UnixSignalsSP. When the constructor without the UnixSignalsSP is specified, the Host's default UnixSignals is used.
* adds a host-specific version of GetUnixSignals() that is used when we need the host's appropriate UnixSignals variant.
* replaces GetUnixSignals() overrides in PlatformElfCore, ProcessGDBRemote, ProcessFreeBSD and ProcessLinux with code that appropriately sets the Process::UnixSignals for the process.
This change also enables some future patches that will enable llgs to be used for local Linux debugging.
llvm-svn: 216748
For hosts that cannot support long thread names, shrink the host
wait4 thread name so that it does not truncate the PID in the thread name.
Change by Shawn Best.
llvm-svn: 216686
LLDB had implemented its own DynamicLibrary class for plugin
support. LLVM has an equivalent mechanism, so this patch deletes
the duplicated code in LLDB and updates LLDB to reference the
mechanism provided by LLVM.
llvm-svn: 216606
This should bring HostInfo up to 99% completion. The remainder
of code in Host will be split into instantiatable classes
representing host processes, threads, dynamic libraries, and
process launching strategies.
llvm-svn: 216230
This continues the effort to get Host code moved over to HostInfo,
and removes many more instances of preprocessor defines along the
way.
llvm-svn: 216195
This patch creates a HostInfo class, a static class used to answer
basic queries about the host platform. As part of this change,
some functionality is moved from Host to HostInfo, and relevant
fixups are performed in the rest of the codebase.
This is part of a larger effort to isolate more code in the Host
layer into platform-specific groups, to make it easier to make
platform specific changes for a particular Host without breaking
other hosts.
Reviewed by: Greg Clayton
Differential Revision: http://reviews.llvm.org/D4963
llvm-svn: 215992
More specifically, this change can be summarized as follows:
1) Makes an lldbHostPosix library which contains code common to
all posix platforms.
2) Creates Host/FileSystem.h which defines a common FileSystem
interface.
3) Implements FileSystem.h in Host/windows and Host/posix.
4) Creates Host/FileCache.h, implemented in Host/common, which
defines a class useful for storing handles to open files needed
by the debugger.
Differential Revision: http://reviews.llvm.org/D4889
llvm-svn: 215775
FileAction was previously a nested class in ProcessLaunchInfo.
This led to some unfortunate style consequences, such as requiring
the AddPosixSpawnFileAction() funciton to be defined in the Target
layer, instead of the more appropriate Host layer. This patch
makes FileAction its own independent class in the Target layer,
and then moves AddPosixSpawnFileAction() into Host as a result.
Differential Revision: http://reviews.llvm.org/D4877
llvm-svn: 215649
This patch adds the notion of a "path syntax" to FileSpec. There
are two syntaxes (Posix and Windows) and one "meta syntax",
Host Native, which uses the current platform to figure out the
appropriate syntax for host paths.
This allows paths from one platform to be represented and
manipulated on another platform even if they have different path
syntaxes.
llvm-svn: 215123
Also fixed the host 32 and 64 bit arch to return "x86_64-apple-macosx" again instead of "x86_64-apple-" (unspecified OS) after recent changes.
<rdar://problem/17845078>
llvm-svn: 214223
Assuming that the user's home directory is at ~ is incorrect on
Windows. This patch delegates the request to LLVM's support
library, which already provides a cross-platform implementation
of this function.
Differential Revision: http://reviews.llvm.org/D4674
llvm-svn: 214093
This change enables lldb-platform for Linux. In addition, it does the following:
* fixes Host::GetLLDBPath() to work on Linux/*BSD for ePathTypeSupportExecutableDir-relative paths.
* adds more logging and comments around lldb-platform startup and remote lldb-platform usage.
* refactors lldb-platform remote-* support for Darwin and Linux into PlatformPOSIX. This, in theory, is the bulk of what is needed for *BSD to make remote connections to lldb-platform as well (although I haven't tested that yet). FreeBSD can make similar changes to their Platform* as was made here for PlatformLinux to pick up the rest of the bits.
* teaches GDBRemoteCommunication to use lldb-gdbserver for non-Apple hosts.
llvm-svn: 213707
reinterpret_cast may not convert a pointer-to-function to a
void-pointer. Take a detour through intptr_t and *then* convert to a
pointer-to-function.
This silences a warning emitted by GCC when building LLDB.
Differential Revision: http://reviews.llvm.org/D4631
llvm-svn: 213693
lldb -P, which outputs its python path, works by using Host-layer
facilities to get information about the loaded python module. This
Host functionality was unimplemented on Windows, so this patch
implements it. Additionally, it removes a pexpect dependency from
the test runner and uses an equivalent invocation of subprocess.
Reviewed by: Todd Fiala
Differential Revision: http://reviews.llvm.org/D4548
llvm-svn: 213410
This value gets set to a max uint32_t value when there is no known limit; otherwise,
it is set to a value appropriate for the platform. For the moment, only
Linux, FreeBSD and NetBSD set it to 16. All other platforms set it to
the max uint32_t value.
Modifies the Process private state thread names to fit within a 16-character limit
when the max thread name length is <= 16. These guarantee that the thread names
can be distinguished within the first 16 characters. Prior to this change, those
threads had names in the final dotted name segment that were not distinguishable
within the first 16 characters.
llvm-svn: 213183
This patch implements basic functionality of the "platform process
list" command for Windows. Currently this has the following
limitations.
* Certain types of filtering are not enabled (e.g. filtering by
architecture with -a), although most filters work.
* The username of the process is not yet obtained.
* Using -v to list verbose information generates an error.
* The architecture column displays the entire triple, leading to
misaligned formatting of the printed table.
Reviewed by: Greg Clayton
Differential Revision: http://reviews.llvm.org/D4413
llvm-svn: 212510
Replace adhoc inline implementation of llvm::array_lengthof in favour of the
implementation in LLVM. This is simply a cleanup change, no functional change
intended.
llvm-svn: 211868
This is a purely mechanical change explicitly casting any parameters for printf
style conversion. This cleans up the warnings emitted by gcc 4.8 on Linux.
llvm-svn: 205607
This is a mechanical change addressing the various sign comparison warnings that
are identified by both clang and gcc. This helps cleanup some of the warning
spew that occurs during builds.
llvm-svn: 205390
These changes were written by Greg Clayton, Jim Ingham, Jason Molenda.
It builds cleanly against TOT llvm with xcodebuild. I updated the
cmake files by visual inspection but did not try a build. I haven't
built these sources on any non-Mac platforms - I don't think this
patch adds any code that requires darwin, but please let me know if
I missed something.
In debugserver, MachProcess.cpp and MachTask.cpp were renamed to
MachProcess.mm and MachTask.mm as they picked up some new Objective-C
code needed to launch processes when running on iOS.
llvm-svn: 205113
(lldb) b puts
(lldb) expr -g -i0 -- (int)puts("hello")
First we will stop at the entry point of the expression before it runs, then we can step over a few times and hit the breakpoint in "puts", then we can continue and finishing stepping and fininsh the expression.
Main features:
- New ObjectFileJIT class that can be easily created for JIT functions
- debug info can now be enabled when parsing expressions
- source for any function that is run throught the JIT is now saved in LLDB process specific temp directory and cleaned up on exit
- "expr -g --" allows you to single step through your expression function with source code
<rdar://problem/16382881>
llvm-svn: 204682
This reverts Host.cpp LaunchProcess spawn behavior on FreeBSD to be
like Linux (and unlike OS X) with regards to how default signal
handlers and setup on the spawned process. FreeBSD does not reset
default signal handlers on the spawned process after this change.
llvm-svn: 199908
This fixes a bug under Linux where spawning a process via
Host::LaunchProcess was disabling all blockable signals on the
launched process. This caused strange behavior when attempting
to kill the lldb-gdbserver process, as the child generally would
not die unless killed with a non-blockable signal (e.g. 'kill -9').
This change moves several functions out of macosx/Host.mm into
common/Host.cpp. In addition, two functions that needed to work
across common/Host.cpp and macosx/Host.mm were moved into the Host.h
header file.
llvm-svn: 199856
This change does the following:
* Adds Makefile build scripts to debug server.
* Fixes a few small mistakes in the other makefiles.
* Modifies generate-vers.pl slightly to also work for debugserver.
* Changes the OS X, non-framework python search path from libdir to
libdir/python2.X/site-packages where it is installed by the build
system (also where it is installed on other operating systems).
Patch by Keno Fischer.
llvm-svn: 199543
ArchSpec now contains an optional distribution_id, with getters and
setters. Host::GetArchitecture () sets it on non-Apple platforms using
Host::GetDistributionId (). The distribution_id is ignored during
ArchSpec comparisons.
The gdb remote qHostInfo message transmits it, if set, via the
distribution_id={id-value} key/value pair. Updated gdb remote docs to
reflect this change.
As before, GetDistributionId () returns nothing on non-Linux platforms
at this time. On Linux, it is returned only if the lsb_platform
command is installed (in /bin or /usr/bin), and only if the
distributor id key is returned by 'lsb_platform -i'. This id is
lowercased, and whitespace is replaced with underscores.
llvm-svn: 199539
The Linux distribution will be added to the ArchSpec class in an
upcoming change. This change only undoes the change to the triple. The
distribution retrieval logic and enabling of lldb-gdbserver for linux
x86_64 builds is still in place.
llvm-svn: 199520
This change does the following:
* enables building lldb-gdbserver on linux_x86-64 platforms.
Note - it builds but it has several run-time issues where many gdb
remote protocol features are not properly implemented yet. I'm
working on these one at a time.
* lldb-gdbserver: does not enable the eLaunchFlagDebug launch flag on
Linux. Currently the POSIX launch routine will assert if that flag
is passed in, presumably because that launch mode is not yet
available. This prevents lldb-gdbserver from asserting the moment
it launches the debuggee process.
* Adds ConstString& Host::GetDistributionId ()
This method is defined to return an empty result on all platforms
except for Linux. On Linux, it makes one attempt to execute
'lsb_release -i' (both /usr/bin/lsb_release, where it appears
on ubuntu, and /bin/lsb_release, where it appears on fedora
if the redhat-lsb package is installed). If lsb_release is not
found in either of those locations, or if 'lsb_release -i' does
not return the first line starting with "Distributor ID:\t",
then the distribution id is empty. The method will lower-case
the id and replace whitespace with underscores.
* Modify Host::GetArchitecture () so that linux replaces an unknown
vendor portion with the results of GetDistributionId () if that
is non-empty. This shows up now in qHostInfo remote packet
responses and on the lldb host side. Tested with ubuntu and
fedora (the latter both with the default of not having lsb_release
installed, and with having lsb_release installed via the redhat-lsb
package).
Examples of triples on Linux after this change:
# x86_64 Unbuntu 12.04 LTS:
x86_64-ubuntu-linux-gnu
# x86_64 Fedora 20 Desktop with redhat-lsb package installed
x86_64-fedora-linux-gnu
# x86_64 Fedora 20 Desktop without redhat-lsb-core installed
# (i.e. no /bin/lsb_release available)
# same as before the change
x86_64--linux-gnu
Note I intend to have Android respond with:
{arch}-android-linux
when I get to implementing Android lldb-gdbserver support.
llvm-svn: 199510
This will get the temporary directory on the current system.
Removed a call to tmpnam() and replaced it with a call to mktemp() using a template that will be in the temp directory.
llvm-svn: 196397
Added _WIN32 guards to new platform features. Using correct SetErrorStringWithFormat within Host when LLDB_DISABLE_POSIX is defined. Also fixed an if defined block.
llvm-svn: 195766
Improved the detection of a valid GDB server where we actually can connect to a socket, but then it doesn't read or write anything (which happens with some USB mux software).
Host::MakeDirectory() now can make as many intermediate directories as needed.
The testsuite now has very initial support for remote test suite running. When running on a remote platform, the setUp function for the test will make a new directory and select it as the working directory on the remote host.
Added a common function that can be used to create the short option string for getopt_long calls.
llvm-svn: 195541
Zachary Turner