llvm dev - Aug 2015 - Linking existing functions from JITed code

Hi Andy,

I haven't tested this on Linux, but on MacOS the
RuntimeDyldMemorManager::getSymbolAddressInProcess method should find
symbol addresses in the host program, including symbols from static
archives linked into the program. However, one gotcha is that the symbol
has to be reachable from main, otherwise the linker may strip it from the
final executable.

Do you have a test-case that I could try to reproduce the issue with?

Alternatively, if you run the code under a debugger, do you see symbols
that the JIT failed to find? If the symbols are visible in the debugger but
invisible to the JIT that sounds like a bug in the JIT. If the symbols are
invisible in both that would suggest that the linker is stripping them out.

- Lang.


On Thu, Aug 13, 2015 at 1:12 PM, David Blaikie <dblaikie at gmail.com>
wrote:
> +"Lang Hames, Linker of Linkers"
>
> (Lang developed the ORC JIT you seem to be using & can provide more
> context than I have)
>
> On Thu, Aug 13, 2015 at 12:43 PM, Andy Somogyi via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi
>>
>> I’ve previously used the ExecutionEngine::addGlobalMapping to make
>> existing functions available to my JITed code.
>>
>> I’m currently using ORC, as MCJIT does not appear to be maintained any
>> longer (the kaleidoscope examples have not worked for some time with
>> MCJIT).
>>
>> I’m using just the basic ORC CompileLayer directly.
>>
>> So, I’ve essentially copied the ExecutionEngine::addGlobalMapping
related
>> function to my JIT context, and I create a lambda resolver as such:
>>
>> JITContext::addModule(…) {
>>
>> auto Resolver = createLambdaResolver(
>> [&](const std::string &name) {
>>
>> // look up first in JIT'ed code
>> if (auto sym = findMangledSymbol(name)) {
>> return RuntimeDyld::SymbolInfo(sym.getAddress(),
>> sym.getFlags());
>> return RuntimeDyld::SymbolInfo(nullptr);
>> }
>>
>> // look up in added globals
>> if (auto addr = getPointerToGlobalMapping(name)) {
>> return RuntimeDyld::SymbolInfo(addr, JITSymbolFlags::Exported);
>> }
>>
>> // finally try to look up existing process symbols, note
>> // this works for symbols loaded in shared libraries, but
>> // does NOT seem to find symbols declared in the executable.
>> if (auto Addr >>
RTDyldMemoryManager::getSymbolAddressInProcess(name)) {
>> return RuntimeDyld::SymbolInfo(Addr, JITSymbolFlags::Exported);
>> }
>> },
>> [](const std::string &S) { return nullptr; }
>> );
>> }
>>
>> Here the getPointerToGlobalMapping function looks in a uint64 StringMap
>> into which values are added via the addGlobalMapping functions.
>>
>>
>> This approach seems to be working, but my question is do you suppose
>> there any are issues with such an approach?
>>
>> The troubling thing is why doesn’t  RTDyldMemoryManager::
>> getSymbolAddressInProcess(name)) return an address for a symbol that is
>> defined in either a static library, or in the executable itself.
>>
>> If this approach is correct, in adding the global values to the
context,
>> and looking them up the lambda resolver, in addition to looking up
external
>> symbols, and considering that the ORC kaleidoscope examples do in fact
>> allow external function calls (which are broken currently), should they
be
>> fixed with this approach?
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org         http://llvm.cs.uiuc.edu
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
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After some fiddling with it, it does in fact look like it works as you describe
Lang.

The trick was you had to call 

llvm::sys::DynamicLibrary::LoadLibraryPermanently(nullptr);

to add the currently running process before calling 

llvm::RTDyldMemoryManager::getSymbolAddressInProcess(name);.

Also, all of the function needs to be declared as extern C to avoid name
mangling.

I however think that adding the addGlobalMapping/getPointerToGlobalMapping
functions to the ORC kaleidoscope examples is very useful, as for example one
wants a set of private symbols made available to JITed code.

 
> On Aug 13, 2015, at 7:41 PM, Lang Hames <lhames at gmail.com> wrote:
> 
> Hi Andy,
> 
> I haven't tested this on Linux, but on MacOS the
RuntimeDyldMemorManager::getSymbolAddressInProcess method should find symbol
addresses in the host program, including symbols from static archives linked
into the program. However, one gotcha is that the symbol has to be reachable
from main, otherwise the linker may strip it from the final executable.
> 
> Do you have a test-case that I could try to reproduce the issue with?
> 
> Alternatively, if you run the code under a debugger, do you see symbols
that the JIT failed to find? If the symbols are visible in the debugger but
invisible to the JIT that sounds like a bug in the JIT. If the symbols are
invisible in both that would suggest that the linker is stripping them out.
> 
> - Lang.
> 
> 
> On Thu, Aug 13, 2015 at 1:12 PM, David Blaikie <dblaikie at gmail.com
<mailto:dblaikie at gmail.com>> wrote:
> +"Lang Hames, Linker of Linkers"
> 
> (Lang developed the ORC JIT you seem to be using & can provide more
context than I have)
> 
> On Thu, Aug 13, 2015 at 12:43 PM, Andy Somogyi via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> Hi
> 
> I’ve previously used the ExecutionEngine::addGlobalMapping to make existing
functions available to my JITed code.
> 
> I’m currently using ORC, as MCJIT does not appear to be maintained any
longer (the kaleidoscope examples have not worked for some time with MCJIT).
> 
> I’m using just the basic ORC CompileLayer directly. 
> 
> So, I’ve essentially copied the ExecutionEngine::addGlobalMapping related
function to my JIT context, and I create a lambda resolver as such:
> 
> JITContext::addModule(…) {
> 
> auto Resolver = createLambdaResolver(
> 		[&](const std::string &name) {
> 
> 	// look up first in JIT'ed code
> 	if (auto sym = findMangledSymbol(name)) {
> 		return RuntimeDyld::SymbolInfo(sym.getAddress(),
> 				sym.getFlags());
> 		return RuntimeDyld::SymbolInfo(nullptr);
> 	}
> 
> 	// look up in added globals
> 	if (auto addr = getPointerToGlobalMapping(name)) {
> 		return RuntimeDyld::SymbolInfo(addr, JITSymbolFlags::Exported);
> 	}
> 
> 	// finally try to look up existing process symbols, note
> 	// this works for symbols loaded in shared libraries, but
> 	// does NOT seem to find symbols declared in the executable.
> 	if (auto Addr > 		
RTDyldMemoryManager::getSymbolAddressInProcess(name)) {
> 		return RuntimeDyld::SymbolInfo(Addr, JITSymbolFlags::Exported);
> 	}
> },
> [](const std::string &S) { return nullptr; }
> );
> }
> 
> Here the getPointerToGlobalMapping function looks in a uint64 StringMap
into which values are added via the addGlobalMapping functions.
> 
> 
> This approach seems to be working, but my question is do you suppose there
any are issues with such an approach?
> 
> The troubling thing is why doesn’t 
RTDyldMemoryManager::getSymbolAddressInProcess(name)) return an address for a
symbol that is defined in either a static library, or in the executable itself.
> 
> If this approach is correct, in adding the global values to the context,
and looking them up the lambda resolver, in addition to looking up external
symbols, and considering that the ORC kaleidoscope examples do in fact allow
external function calls (which are broken currently), should they be fixed with
this approach?
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>       
http://llvm.cs.uiuc.edu <http://llvm.cs.uiuc.edu/>
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> 
> 
> 
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Hi Andy,

I think that makes sense. I'm currently rewriting the core Kaleidoscope
tutorials - I'll look at adding support for this.

- Lang.

On Fri, Aug 14, 2015 at 7:38 AM, Andy Somogyi <andy.somogyi at gmail.com>
wrote:
> After some fiddling with it, it does in fact look like it works as you
> describe Lang.
>
> The trick was you had to call
>
> llvm::sys::DynamicLibrary::LoadLibraryPermanently(nullptr);
>
> to add the currently running process before calling
>
> llvm::RTDyldMemoryManager::getSymbolAddressInProcess(name);.
>
> Also, all of the function needs to be declared as extern C to avoid name
> mangling.
>
> I however think that adding the addGlobalMapping/getPointerToGlobalMapping
> functions to the ORC kaleidoscope examples is very useful, as for example
> one wants a set of private symbols made available to JITed code.
>
>
>
> On Aug 13, 2015, at 7:41 PM, Lang Hames <lhames at gmail.com> wrote:
>
> Hi Andy,
>
> I haven't tested this on Linux, but on MacOS the
> RuntimeDyldMemorManager::getSymbolAddressInProcess method should find
> symbol addresses in the host program, including symbols from static
> archives linked into the program. However, one gotcha is that the symbol
> has to be reachable from main, otherwise the linker may strip it from the
> final executable.
>
> Do you have a test-case that I could try to reproduce the issue with?
>
> Alternatively, if you run the code under a debugger, do you see symbols
> that the JIT failed to find? If the symbols are visible in the debugger but
> invisible to the JIT that sounds like a bug in the JIT. If the symbols are
> invisible in both that would suggest that the linker is stripping them out.
>
> - Lang.
>
>
> On Thu, Aug 13, 2015 at 1:12 PM, David Blaikie <dblaikie at
gmail.com> wrote:
>
>> +"Lang Hames, Linker of Linkers"
>>
>> (Lang developed the ORC JIT you seem to be using & can provide more
>> context than I have)
>>
>> On Thu, Aug 13, 2015 at 12:43 PM, Andy Somogyi via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi
>>>
>>> I’ve previously used the ExecutionEngine::addGlobalMapping to make
>>> existing functions available to my JITed code.
>>>
>>> I’m currently using ORC, as MCJIT does not appear to be maintained
any
>>> longer (the kaleidoscope examples have not worked for some time
with
>>> MCJIT).
>>>
>>> I’m using just the basic ORC CompileLayer directly.
>>>
>>> So, I’ve essentially copied the ExecutionEngine::addGlobalMapping
>>> related function to my JIT context, and I create a lambda resolver
as such:
>>>
>>> JITContext::addModule(…) {
>>>
>>> auto Resolver = createLambdaResolver(
>>> [&](const std::string &name) {
>>>
>>> // look up first in JIT'ed code
>>> if (auto sym = findMangledSymbol(name)) {
>>> return RuntimeDyld::SymbolInfo(sym.getAddress(),
>>> sym.getFlags());
>>> return RuntimeDyld::SymbolInfo(nullptr);
>>> }
>>>
>>> // look up in added globals
>>> if (auto addr = getPointerToGlobalMapping(name)) {
>>> return RuntimeDyld::SymbolInfo(addr, JITSymbolFlags::Exported);
>>> }
>>>
>>> // finally try to look up existing process symbols, note
>>> // this works for symbols loaded in shared libraries, but
>>> // does NOT seem to find symbols declared in the executable.
>>> if (auto Addr >>>
RTDyldMemoryManager::getSymbolAddressInProcess(name)) {
>>> return RuntimeDyld::SymbolInfo(Addr, JITSymbolFlags::Exported);
>>> }
>>> },
>>> [](const std::string &S) { return nullptr; }
>>> );
>>> }
>>>
>>> Here the getPointerToGlobalMapping function looks in a uint64
StringMap
>>> into which values are added via the addGlobalMapping functions.
>>>
>>>
>>> This approach seems to be working, but my question is do you
suppose
>>> there any are issues with such an approach?
>>>
>>> The troubling thing is why doesn’t  RTDyldMemoryManager::
>>> getSymbolAddressInProcess(name)) return an address for a symbol
that is
>>> defined in either a static library, or in the executable itself.
>>>
>>> If this approach is correct, in adding the global values to the
context,
>>> and looking them up the lambda resolver, in addition to looking up
external
>>> symbols, and considering that the ORC kaleidoscope examples do in
fact
>>> allow external function calls (which are broken currently), should
they be
>>> fixed with this approach?
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org         http://llvm.cs.uiuc.edu
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>
>
>
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