llvm dev - Nov 2014 - [LLVMdev] [RFC] New ToolsSupport library for stuff that only tools need

I would have preferred the library to be moved out of the “Support” folder and
have its own top-level library and include folder.

Just my 2 cents.
> On Nov 6, 2014, at 2:12 PM, Chris Bieneman <beanz at apple.com>
wrote:
> 
> So, I decided to try and start small. My idea here was create a
ToolsSupport library, and move one small, but important function into the new
library to shake out all the places that would need updating. The function I
chose to start with was llvm::sys::PrintStackTraceOnErrorSignal.
> 
> Turns out this wasn’t so small. These patches aren’t done yet, but since
they’re pretty big I thought I’d send them out for preliminary feedback about
whether or not this is the right approach. The patches contain the following
changes:
> 
> * Patches to LLVM & Clang CMake build systems to add a new
libLLVMToolsSupport
> * New SignalHandlers.h/.cpp/.inc files for PrintStackTraceOnErrorSignal
> * Updated all llvm tools to pull in the new library and use the new header
> 
> Still missing:
> 
> * Windows side of the SignalHandlers patches
> * Autoconf/Make side of the build system patches
> * Patches for other LLVM projects
> * General cleanup
> 
> Feedback is greatly appreciated. I’d really like to make sure I’m not lost
in the weeds on this one.
> 
> Thanks,
> -Chris
> 
> <libLLVMToolsSupport.diff>
> <libLLVMToolsSupport-clang.diff>
> 
> 
> 
>> On Oct 31, 2014, at 2:07 PM, Chris Bieneman <beanz at apple.com
<mailto:beanz at apple.com>> wrote:
>> 
>> I was thinking of moving the files into a Tools subdirectory of
Support, and having a new library generated from that. Does that mesh with what
you’d like to see?
>> 
>> I’ve gotten wrapped into a nasty internal bug hunt, so I probably won’t
have patches until next week. I will also probably need to ask Eric for help
with the autoconf side of things because my familiarity with autoconf ends at
“run configure”.
>> 
>> -Chris
>> 
>>> On Oct 31, 2014, at 1:46 PM, Reid Kleckner <rnk at google.com
<mailto:rnk at google.com>> wrote:
>>> 
>>> I'm in favor of splitting the code out into a new directory and
using separate libraries if we're going to do this.
>>> 
>>> Build systems should be really dumb, IMO.
>>> 
>>> On Thu, Oct 30, 2014 at 6:46 PM, Eric Christopher <echristo at
gmail.com <mailto:echristo at gmail.com>> wrote:
>>> +1 to this.
>>> 
>>> I'd slightly prefer a separate library (though moving the code
vs not moving the code I'm relatively apathetic about), but just because I
hate conditional compilation.
>>> 
>>> -eric
>>> 
>>> On Thu Oct 30 2014 at 5:55:59 PM Juergen Ributzka <juergen at
apple.com <mailto:juergen at apple.com>> wrote:
>>> I am mostly impartial to the two proposed solutions (separate
library or conditional compilation of the hooks into the tools). If we make it a
library I think we should make it a convenience library that is intended to be
used only with the tools and not an external supported library at all.
>>> 
>>> -Juergen
>>> 
>>>> On Oct 20, 2014, at 1:02 PM, Chris Bieneman <beanz at
apple.com <mailto:beanz at apple.com>> wrote:
>>>> 
>>>> There is no real technical requirement for this. Currently we
work around the signal handlers by building with ENABLE_CRASH_OVERRIDES=NO, and
carrying along the command line parsing code and ToolOutputFile isn’t really a
big drain.
>>>> 
>>>> This seemed to me like the cleanest way to accomplish a goal of
mine. The goal I have is to be able to build an LLVM dylib and llc/opt/etc from
the same CMake invocation where the dylib does not have crash overrides and
signal handler hooks, but the tools do.
>>>> 
>>>> There are other ways to accomplish this, but I felt that
separating libLLVMSupport into two libraries seemed the cleanest. An alternate
approach that could work for me would be to have the implementation of the hooks
only be compiled into the tools.
>>>> 
>>>> -Chris
>>>> 
>>>>> On Oct 20, 2014, at 12:57 PM, Chandler Carruth
<chandlerc at google.com <mailto:chandlerc at google.com>> wrote:
>>>>> 
>>>>> The question I have is -- does the actual source code need
to move? I'm wondering what aspects require a new library as opposed to
different sequence of things happening when initializing LLVM as a library vs.
as a tool.
>>>>> 
>>>>> (We've definitely had trouble with the signal handlers
ourselves, but I thought we had solved it by using different code paths to set
everything else up...)
>>>>> 
>>>>> On Mon, Oct 20, 2014 at 12:46 PM, Chris Bieneman <beanz
at apple.com <mailto:beanz at apple.com>> wrote:
>>>>> There are some pieces of functionality in LLVM today, that
make sense for tools like llc, opt, clang, but they aren't relevant for
embedded uses like LLVM in the JavaScript JIT. One example of this type of
functionality is the signal handlers.
>>>>> 
>>>>> I'd like to propose migrating content that is
specifically designed for tools into a new ToolsSupport library. My initial
candidates for the new library would be; anything guarded by
ENABLE_CRASH_OVERRIDES, and any functionality specific to tools (i.e.
ToolOutputFile and eventually command line parsing— once it can be factored
out).
>>>>> 
>>>>> The primary goal of this is to make it easy for uses of
LLVM that aren't command line tools to not include functionality that
isn't required for that use case.
>>>>> 
>>>>> Thoughts?
>>>>> 
>>>>> -Chris
>>>>> _______________________________________________
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>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>
>>>>> 
>>>> 
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On Thu, Nov 6, 2014 at 2:42 PM, Juergen Ributzka <juergen at apple.com>
wrote:
> I would have preferred the library to be moved out of the “Support” folder
> and have its own top-level library and include folder.
>
+1, you will need to do this if you want to support the autoconf build
system.

----

Looking at the diff, I now remember why you want to do this. I seem to
recall you want to do this because the Mac-specific code in Support defines
raise(), __assert_rtn(), and abort(), and that's hostile to embedders like
WebKit. Makes sense, it's a gross hack, and I'd be in favor of fixing it
if
possible. If it weren't for this hack, I would recommend that you just
avoid calling PrintStackTraceOnErrorSignal from WebKit.

Is there some way we can prevent this Mac-specific hack from affecting our
library organization? It's not clear to me that the distinction between
Support and ToolsSupport is really worth it.

Most LLVM tools are single threaded and don't need to redirect signals to
the current thread. I think it's only the crash recovery logic that needs
the signal to be delivered to the current thread. Maybe we should factor
out a CrashRecovery library, given that XCode via libclang is basically the
only client of this stuff? Does WebKit want to try to recover from JIT
assertion failures?
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On Thu, Nov 6, 2014 at 5:00 PM, Reid Kleckner <rnk at google.com> wrote:
> Looking at the diff, I now remember why you want to do this. I seem to
> recall you want to do this because the Mac-specific code in Support defines
> raise(), __assert_rtn(), and abort(), and that's hostile to embedders
like
> WebKit. Makes sense, it's a gross hack, and I'd be in favor of
fixing it if
> possible. If it weren't for this hack, I would recommend that you just
> avoid calling PrintStackTraceOnErrorSignal from WebKit.

Sorry I've been absent, but this is actually a much better summary of my
feelings here. I should have written this more clearly when I looked at the
diff, my apologies.
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> On Nov 6, 2014, at 3:00 PM, Reid Kleckner <rnk at google.com> wrote:
> 
> On Thu, Nov 6, 2014 at 2:42 PM, Juergen Ributzka <juergen at apple.com
<mailto:juergen at apple.com>> wrote:
> I would have preferred the library to be moved out of the “Support” folder
and have its own top-level library and include folder.
> 
> +1, you will need to do this if you want to support the autoconf build
system.
This should be a fairly small change to make.
> 
> ----
> 
> Looking at the diff, I now remember why you want to do this. I seem to
recall you want to do this because the Mac-specific code in Support defines
raise(), __assert_rtn(), and abort(), and that's hostile to embedders like
WebKit. Makes sense, it's a gross hack, and I'd be in favor of fixing it
if possible. If it weren't for this hack, I would recommend that you just
avoid calling PrintStackTraceOnErrorSignal from WebKit.
That hack is the primary motivator, but that can be solved other ways. One
option would be for us to move the nasty Mac-specific hack out of the cpp file
and into a header that tools could optionally include.
> 
> Is there some way we can prevent this Mac-specific hack from affecting our
library organization? It's not clear to me that the distinction between
Support and ToolsSupport is really worth it.
> 
> Most LLVM tools are single threaded and don't need to redirect signals
to the current thread. I think it's only the crash recovery logic that needs
the signal to be delivered to the current thread. Maybe we should factor out a
CrashRecovery library, given that XCode via libclang is basically the only
client of this stuff? Does WebKit want to try to recover from JIT assertion
failures?
The other thought I had which motivated this solution was that if we could strip
all the functionality that is only really used by tools out into a separate
library it would offer cleaner organization of code. Support seems to often get
used as a dumping ground for stuff that just doesn’t fit anywhere else.

Based on your feedback and Chandler’s maybe this just isn’t the right
separation. I can look into a solution to address our hackiness without creating
a separate library.

-Chris
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