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edA-qa mort-ora-y via llvm-dev

2018-Apr-18 20:47 UTC

[llvm-dev] A struct {i8, i64} has size == 12, clang says size 16

I think I see a potential issue. My ExecutionEngine setup may not be
using the same target as my object code emitting, and in this test case
I'm running in the ExecutionEngine.  I'll go over this code to ensure
I'm creating the same triple and see if that helps -- I'm assuming it
will, since I can't imagine the exact same triple with clang would
produce a different layout.


On 18/04/18 21:37, Reid Kleckner wrote:> It sounds like your DataLayout may not match clang's for x86_64-linux.
What
> does it say about the alignment of i64?
> On Wed, Apr 18, 2018 at 12:05 PM edA-qa mort-ora-y via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> I'm creating a struct of `{i8,i64}` and
`DataLayout::getTypeAllocSize`
>> is returning `12`. `getStructLayout` also gives an `4` offset for the
>> second element.
>> The native ABI, and clang, for the same type are producing a size of
16,
>> with an alignment of 8, for the second element.
>> This is for the system triple "x86_64-linux-gnu"
>> What could be causing this difference in alignment and how can I fix
it?
>
>> I'm verifying the native ABI with:
>>      // clang -emit-llvm ll_struct_arg.c -S -o /dev/tty
>>      #include <stddef.h>
>>      typedef struct vpt_data {
>>          _Bool c;
>>          long int b;
>>      } vpt_data;
>>      int main() {
>>          vpt_data v;
>>          vpt_test(v);
>>          auto a = sizeof(v);
>>          auto off = offsetof(vpt_data,b);
>>      }
>
>> 16 is stored to `a` and 8 to `off`.
>> --
>> edA-qa mort-ora-y
>>          http://mortoray.com/
>> Creator of the Leaf language
>>          http://leaflang.org/
>> Streaming algorithms, AI, and design on Twitch
>>          https://www.twitch.tv/mortoray
>> Twitter
>>          edaqa
>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

-- 
edA-qa mort-ora-y  
	http://mortoray.com/

Creator of the Leaf language
	http://leaflang.org/

Streaming algorithms, AI, and design on Twitch
	https://www.twitch.tv/mortoray

Twitter
	edaqa

mats petersson via llvm-dev

2018-Apr-19 09:37 UTC

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[llvm-dev] A struct {i8, i64} has size == 12, clang says size 16

What exactly is your alignment settings in your LLVM struct?

Something like this would tell you the alignment of "something".
const llvm::DataLayout dl(theModule);
size_t size = dl.getPrefTypeAlignment(something);
IIn "my" compiler, I don't do anything special to align structs,
so it's
plausibly your specific data-layout that says that i64 only needs aligning
to 32-bits (and clang adjusts it because "it can", by adding extra
padding
elements) - or you're using different targets (or settings for the targets)

--
Mats
On 18 April 2018 at 21:47, edA-qa mort-ora-y via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> I think I see a potential issue. My ExecutionEngine setup may not be
> using the same target as my object code emitting, and in this test case
> I'm running in the ExecutionEngine.  I'll go over this code to
ensure
> I'm creating the same triple and see if that helps -- I'm assuming
it
> will, since I can't imagine the exact same triple with clang would
> produce a different layout.
>
>
> On 18/04/18 21:37, Reid Kleckner wrote:
> > It sounds like your DataLayout may not match clang's for
x86_64-linux.
> What
> > does it say about the alignment of i64?
> > On Wed, Apr 18, 2018 at 12:05 PM edA-qa mort-ora-y via llvm-dev <
> > llvm-dev at lists.llvm.org> wrote:
> >
> >> I'm creating a struct of `{i8,i64}` and
`DataLayout::getTypeAllocSize`
> >> is returning `12`. `getStructLayout` also gives an `4` offset for
the
> >> second element.
> >> The native ABI, and clang, for the same type are producing a size
of 16,
> >> with an alignment of 8, for the second element.
> >> This is for the system triple "x86_64-linux-gnu"
> >> What could be causing this difference in alignment and how can I
fix it?
> >
> >> I'm verifying the native ABI with:
> >>      // clang -emit-llvm ll_struct_arg.c -S -o /dev/tty
> >>      #include <stddef.h>
> >>      typedef struct vpt_data {
> >>          _Bool c;
> >>          long int b;
> >>      } vpt_data;
> >>      int main() {
> >>          vpt_data v;
> >>          vpt_test(v);
> >>          auto a = sizeof(v);
> >>          auto off = offsetof(vpt_data,b);
> >>      }
> >
> >> 16 is stored to `a` and 8 to `off`.
> >> --
> >> edA-qa mort-ora-y
> >>          http://mortoray.com/
> >> Creator of the Leaf language
> >>          http://leaflang.org/
> >> Streaming algorithms, AI, and design on Twitch
> >>          https://www.twitch.tv/mortoray
> >> Twitter
> >>          edaqa
> >
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
> --
> edA-qa mort-ora-y
>         http://mortoray.com/
>
> Creator of the Leaf language
>         http://leaflang.org/
>
> Streaming algorithms, AI, and design on Twitch
>         https://www.twitch.tv/mortoray
>
> Twitter
>         edaqa
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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edA-qa mort-ora-y via llvm-dev

2018-Apr-19 09:47 UTC

head link

[llvm-dev] A struct {i8, i64} has size == 12, clang says size 16

I think I've figured it out now. The setup of my triple/datalayout for
the module was apparently not correct. It likely worked mainly to this
point since the default dataLayout is close to the host ABI, but not quite.

I have the following setup, which appears to work:

    module = new llvm::Module( "test", *llvm_context );
    module->setTargetTriple( platform::target->triple );
//x86_64-pc-linux-gnu
   
    std::string err_str;
    auto triple_str = llvm::Triple::normalize(platform::target->triple);
    llvm::Target const *  target = llvm::TargetRegistry::lookupTarget(
triple_str, err_str );
    STATE_CHECK( target, err_str ); //assert target != nullptr
    auto targetMachine = target->createTargetMachine(triple_str,
"generic", "", llvm::TargetOptions{},
        llvm::Optional<llvm::Reloc::Model>());
   
    module->setDataLayout( targetMachine->createDataLayout() );

I'll be testing on Mac later today, but I suspect it has the same data
layout.



On 19/04/18 11:37, mats petersson wrote:> What exactly is your alignment settings in your LLVM struct?
>
> Something like this would tell you the alignment of "something".
> const llvm::DataLayout dl(theModule);
> size_t size = dl.getPrefTypeAlignment(something);
>
> IIn "my" compiler, I don't do anything special to align
structs, so
> it's plausibly your specific data-layout that says that i64 only needs
> aligning to 32-bits (and clang adjusts it because "it can", by
adding
> extra padding elements) - or you're using different targets (or
> settings for the targets)
>
> --
> Mats
> On 18 April 2018 at 21:47, edA-qa mort-ora-y via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>
>     I think I see a potential issue. My ExecutionEngine setup may not be
>     using the same target as my object code emitting, and in this test
>     case
>     I'm running in the ExecutionEngine.  I'll go over this code to
ensure
>     I'm creating the same triple and see if that helps -- I'm
assuming it
>     will, since I can't imagine the exact same triple with clang would
>     produce a different layout.
>
>
>     On 18/04/18 21:37, Reid Kleckner wrote:
>     > It sounds like your DataLayout may not match clang's for
>     x86_64-linux. What
>     > does it say about the alignment of i64?
>     > On Wed, Apr 18, 2018 at 12:05 PM edA-qa mort-ora-y via llvm-dev
<
>     > llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>     >
>     >> I'm creating a struct of `{i8,i64}` and
>     `DataLayout::getTypeAllocSize`
>     >> is returning `12`. `getStructLayout` also gives an `4` offset
>     for the
>     >> second element.
>     >> The native ABI, and clang, for the same type are producing a
>     size of 16,
>     >> with an alignment of 8, for the second element.
>     >> This is for the system triple "x86_64-linux-gnu"
>     >> What could be causing this difference in alignment and how can
>     I fix it?
>     >
>     >> I'm verifying the native ABI with:
>     >>      // clang -emit-llvm ll_struct_arg.c -S -o /dev/tty
>     >>      #include <stddef.h>
>     >>      typedef struct vpt_data {
>     >>          _Bool c;
>     >>          long int b;
>     >>      } vpt_data;
>     >>      int main() {
>     >>          vpt_data v;
>     >>          vpt_test(v);
>     >>          auto a = sizeof(v);
>     >>          auto off = offsetof(vpt_data,b);
>     >>      }
>     >
>     >> 16 is stored to `a` and 8 to `off`.
>     >> --
>     >> edA-qa mort-ora-y
>     >>          http://mortoray.com/
>     >> Creator of the Leaf language
>     >>          http://leaflang.org/
>     >> Streaming algorithms, AI, and design on Twitch
>     >>          https://www.twitch.tv/mortoray
>     >> Twitter
>     >>          edaqa
>     >
>     >> _______________________________________________
>     >> LLVM Developers mailing list
>     >> llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
>     >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>     <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>
>
>     -- 
>     edA-qa mort-ora-y 
>             http://mortoray.com/
>
>     Creator of the Leaf language
>             http://leaflang.org/
>
>     Streaming algorithms, AI, and design on Twitch
>             https://www.twitch.tv/mortoray
>
>     Twitter
>             edaqa
>
>
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>     <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>
>
-- 
edA-qa mort-ora-y  
	http://mortoray.com/

Creator of the Leaf language
	http://leaflang.org/

Streaming algorithms, AI, and design on Twitch
	https://www.twitch.tv/mortoray

Twitter
	edaqa
	

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