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Xu Yang

2009-Nov-18 05:02 UTC

[LLVMdev] lli -force-interpreter complains about external function

Hi Nick:

Thanks for pointing me to libffi.
Recompile LLVM with libffi does solve the problem of printf.
But it still has other problems:
1) sinf() returns 0 in the interpreter, but returns correct value in JIT
(see hellosin.c)
2) calling pthread_create cause lli to crash in the interpreter mode, but no
problem in JIT (see phello.c).

My questions are:
i) can I call any arbitrary external function in the interpreter?
ii) how do I specify the dynamic library (where the external function is
implemented), when I call the interpreter?

Thanks
Xu

hellosin.c
======================#include <stdio.h>
#include <math.h>


int main(int argc, char** argv){
  float f = sinf(0.5235988f);
  printf("hello sin: %10.2f\n", f);
  return 0;
}
=======================$ llvm-gcc -o hellosin.bc -emit-llvm -c hellosin.c
$ lli -force-interpreter=true hellosin.bc
hello sin:       0.00
$ lli hellosin.bc
hello sin:       0.50

phello.c
=======================#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS     4

void *PrintHello(void *threadid)
{
   long tid;
   tid = (long)threadid;
   printf("Hello from %ld.\n", tid);
   pthread_exit(NULL);
}

int main (int argc, char *argv[])
{
   pthread_t threads[NUM_THREADS];
   int ret;
   long t;
   for(t=0; t<NUM_THREADS; t++){
#ifdef DEBUG
      printf("creating thread %ld\n", t);
#endif
      ret = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
      if (ret){
         printf("pthread_create ERROR: %d\n", ret);
         return(-1);
      }
   }
   pthread_exit(NULL);
}
=======================$ llvm-gcc -o phello.bc -emit-llvm -c phello.c
$ lli -force-interpreter=true phello.bc
0   lli 0x08796bf8
Segmentation fault
$ lli phello.bc
Hello from 0.
Hello from 1.
Hello from 2.
Hello from 3.


On Tue, Nov 17, 2009 at 2:52 AM, Nick Lewycky <nicholas at mxc.ca> wrote:
> Timo Juhani Lindfors wrote:
>
>> Nick Lewycky<nicholas at mxc.ca>  writes:
>>
>>> The interpreter uses libffi to make external function calls.
However, it
>>> needs to be detected at LLVM's compile time. If you're
using the
>>> released packages, we disabled that because we were worried about
users
>>> who don't have libffi installed.
>>>
>>
>> This seems to be quite a common problem (I too hit it once, thought it
>> was a bug and reported it at
>> http://llvm.org/bugs/show_bug.cgi?id=5466) how about making lli inform
>> the user that LLVM was built without FFI support?
>>
>
> Thanks for the reminder. I recall looking at the patch but I didn't
apply
> it at the time because I couldn't figure out why the code above it used
> errs() in one case and llvm_report_error in another.
>
> Nick
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Xu Yang

2009-Nov-18 05:29 UTC

head link

[LLVMdev] lli -force-interpreter complains about external function

Hi Nick:

The first problem have been solved by calling llvm-ld:

$ llvm-ld -o hellosin.llvm hellosin.bc -lm
$ lli -force-interpreter=true -load=/usr/lib/libm.so hellosin.llvm.bc
hello sin:       0.50

The pthread problem remains after llvm-ld:

$ lli -force-interpreter=true -load=/lib/libpthread.so.0 phello.llvm.bc
0   lli 0x08796bf8
Segmentation fault


For those who are getting "invalid ELF header" error when calling
llvm-ld
with -lpthread,
please change the load module from /usr/lib/pthread.a to
/lib/libpthread.so.0.

Thanks
Xu

On Wed, Nov 18, 2009 at 12:02 AM, Xu Yang <yangx2000 at gmail.com> wrote:
> Hi Nick:
>
> Thanks for pointing me to libffi.
> Recompile LLVM with libffi does solve the problem of printf.
> But it still has other problems:
> 1) sinf() returns 0 in the interpreter, but returns correct value in JIT
> (see hellosin.c)
> 2) calling pthread_create cause lli to crash in the interpreter mode, but
> no problem in JIT (see phello.c).
>
> My questions are:
> i) can I call any arbitrary external function in the interpreter?
> ii) how do I specify the dynamic library (where the external function is
> implemented), when I call the interpreter?
>
> Thanks
> Xu
>
> hellosin.c
> ======================> #include <stdio.h>
> #include <math.h>
>
>
> int main(int argc, char** argv){
>   float f = sinf(0.5235988f);
>   printf("hello sin: %10.2f\n", f);
>   return 0;
> }
> =======================> $ llvm-gcc -o hellosin.bc -emit-llvm -c
hellosin.c
> $ lli -force-interpreter=true hellosin.bc
> hello sin:       0.00
> $ lli hellosin.bc
> hello sin:       0.50
>
> phello.c
> =======================> #include <pthread.h>
> #include <stdio.h>
> #define NUM_THREADS     4
>
> void *PrintHello(void *threadid)
> {
>    long tid;
>    tid = (long)threadid;
>    printf("Hello from %ld.\n", tid);
>    pthread_exit(NULL);
> }
>
> int main (int argc, char *argv[])
> {
>    pthread_t threads[NUM_THREADS];
>    int ret;
>    long t;
>    for(t=0; t<NUM_THREADS; t++){
> #ifdef DEBUG
>       printf("creating thread %ld\n", t);
> #endif
>       ret = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
>       if (ret){
>          printf("pthread_create ERROR: %d\n", ret);
>          return(-1);
>       }
>    }
>    pthread_exit(NULL);
> }
> =======================> $ llvm-gcc -o phello.bc -emit-llvm -c phello.c
> $ lli -force-interpreter=true phello.bc
> 0   lli 0x08796bf8
> Segmentation fault
> $ lli phello.bc
> Hello from 0.
> Hello from 1.
> Hello from 2.
> Hello from 3.
>
>
> On Tue, Nov 17, 2009 at 2:52 AM, Nick Lewycky <nicholas at mxc.ca>
wrote:
>
>> Timo Juhani Lindfors wrote:
>>
>>> Nick Lewycky<nicholas at mxc.ca>  writes:
>>>
>>>> The interpreter uses libffi to make external function calls.
However, it
>>>> needs to be detected at LLVM's compile time. If you're
using the
>>>> released packages, we disabled that because we were worried
about users
>>>> who don't have libffi installed.
>>>>
>>>
>>> This seems to be quite a common problem (I too hit it once, thought
it
>>> was a bug and reported it at
>>> http://llvm.org/bugs/show_bug.cgi?id=5466) how about making lli
inform
>>> the user that LLVM was built without FFI support?
>>>
>>
>> Thanks for the reminder. I recall looking at the patch but I didn't
apply
>> it at the time because I couldn't figure out why the code above it
used
>> errs() in one case and llvm_report_error in another.
>>
>> Nick
>>
>
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Nick Lewycky

2009-Nov-18 05:40 UTC

head link

[LLVMdev] lli -force-interpreter complains about external function

Xu Yang wrote:> Hi Nick:
>
> The first problem have been solved by calling llvm-ld:
>
> $ llvm-ld -o hellosin.llvm hellosin.bc -lm
> $ lli -force-interpreter=true -load=/usr/lib/libm.so hellosin.llvm.bc
> hello sin:       0.50
Only because the optimizer saw sin(constant) and folded it away. The 
entire program became 'print constant string'. There is certainly a bug 
calling sinf() from the interpreter but I don't know what it is yet.
> The pthread problem remains after llvm-ld:
>
> $ lli -force-interpreter=true -load=/lib/libpthread.so.0 phello.llvm.bc
> 0   lli 0x08796bf8
> Segmentation fault
I don't expect this to work at all. Unlike the JIT, I don't know of any 
work having been done to make the interpreter thread-safe.

By the way, the interpreter can't support many more things, such as 
qsort() or any method which expects to call a function pointer. Is there 
a reason you need to use the interpreter? It's been largely 
undermaintained because it's pretty much useless when you've got a 
working JIT.

Nick
> For those who are getting "invalid ELF header" error when calling
> llvm-ld with -lpthread,
> please change the load module from /usr/lib/pthread.a to
> /lib/libpthread.so.0.
>
> Thanks
> Xu
>
> On Wed, Nov 18, 2009 at 12:02 AM, Xu Yang <yangx2000 at gmail.com
> <mailto:yangx2000 at gmail.com>> wrote:
>
>     Hi Nick:
>
>     Thanks for pointing me to libffi.
>     Recompile LLVM with libffi does solve the problem of printf.
>     But it still has other problems:
>     1) sinf() returns 0 in the interpreter, but returns correct value in
>     JIT (see hellosin.c)
>     2) calling pthread_create cause lli to crash in the interpreter
>     mode, but no problem in JIT (see phello.c).
>
>     My questions are:
>     i) can I call any arbitrary external function in the interpreter?
>     ii) how do I specify the dynamic library (where the external
>     function is implemented), when I call the interpreter?
>
>     Thanks
>     Xu
>
>     hellosin.c
>     ======================>     #include <stdio.h>
>     #include <math.h>
>
>
>     int main(int argc, char** argv){
>        float f = sinf(0.5235988f);
>        printf("hello sin: %10.2f\n", f);
>        return 0;
>     }
>     =======================>     $ llvm-gcc -o hellosin.bc -emit-llvm -c
hellosin.c
>     $ lli -force-interpreter=true hellosin.bc
>     hello sin:       0.00
>     $ lli hellosin.bc
>     hello sin:       0.50
>
>     phello.c
>     =======================>     #include <pthread.h>
>     #include <stdio.h>
>     #define NUM_THREADS     4
>
>     void *PrintHello(void *threadid)
>     {
>         long tid;
>         tid = (long)threadid;
>         printf("Hello from %ld.\n", tid);
>         pthread_exit(NULL);
>     }
>
>     int main (int argc, char *argv[])
>     {
>         pthread_t threads[NUM_THREADS];
>         int ret;
>         long t;
>         for(t=0; t<NUM_THREADS; t++){
>     #ifdef DEBUG
>            printf("creating thread %ld\n", t);
>     #endif
>            ret = pthread_create(&threads[t], NULL, PrintHello, (void
*)t);
>            if (ret){
>               printf("pthread_create ERROR: %d\n", ret);
>               return(-1);
>            }
>         }
>         pthread_exit(NULL);
>     }
>     =======================>     $ llvm-gcc -o phello.bc -emit-llvm -c
phello.c
>     $ lli -force-interpreter=true phello.bc
>     0   lli 0x08796bf8
>     Segmentation fault
>     $ lli phello.bc
>     Hello from 0.
>     Hello from 1.
>     Hello from 2.
>     Hello from 3.
>
>
>     On Tue, Nov 17, 2009 at 2:52 AM, Nick Lewycky <nicholas at mxc.ca
>     <mailto:nicholas at mxc.ca>> wrote:
>
>         Timo Juhani Lindfors wrote:
>
>             Nick Lewycky<nicholas at mxc.ca <mailto:nicholas at
mxc.ca>>  writes:
>
>                 The interpreter uses libffi to make external function
>                 calls. However, it
>                 needs to be detected at LLVM's compile time. If
you're
>                 using the
>                 released packages, we disabled that because we were
>                 worried about users
>                 who don't have libffi installed.
>
>
>             This seems to be quite a common problem (I too hit it once,
>             thought it
>             was a bug and reported it at
>             http://llvm.org/bugs/show_bug.cgi?id=5466) how about making
>             lli inform
>             the user that LLVM was built without FFI support?
>
>
>         Thanks for the reminder. I recall looking at the patch but I
>         didn't apply it at the time because I couldn't figure out
why
>         the code above it used errs() in one case and llvm_report_error
>         in another.
>
>         Nick
>
>
>

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