[Vm-dev] __builtin_extract_return_addr

Fri Sep 18 10:47:58 UTC 2020

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I don't know whether the following comment makes sense,
but shouldn't this code be in:

cogitX64SysV.c or cogitIA32.c

in the directory spur64src/vm/ and spursrc/vm ?

Basically it seems cointerp.c in spur64src/vm/cointerp.c is using
getReturnAddress()

And this is ABI specific so should be in spur64src/vm/cogitX64SysV.c ??
(or cogitIA32.c?) right ?

Anyway I tried your code (it is after all your choice), even if I don't
quite like the idea of the assembly language inline.

The code seems to compile and work for i386 (the easy case I think,
since my understanding is the IA32 ABI makes this easier).

I can open the Cog VM and run Squeak6.0alpha-19547-32bit.zip (image 32bit).

However the X64 case is harder.  That did not compile at first.

It's been a long time that I've looked at assembly language,
but the movl instruction is probably not the right one for %rax.

I changed it to "movq" instead of "movl" and that seems to work.

So good news is that with your suggested code, it works for
32bit and 64bit again on Solaris 11.4 .

I say again because COG was already working on Solaris 11.4 until you
made the change for the getReturnAddress.

I tried on 64bit on Solaris 11.4 with Squeak6.0alpha-19793-64bit.image.

David Stes

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----- Op 18 sep 2020 om 6:20 schreef Eliot Miranda eliot.miranda at gmail.com:

> Hi David,
> 
> On Thu, Sep 17, 2020 at 9:58 AM stes at PANDORA.BE <stes at telenet.be> wrote:
> 
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>>
>> Hi,
>>
>> Originally when I compiled on Solaris, I had both the "Cog" and "Stack" VM
>> working.
>>
>> Unfortunately there was a change in april which breaks the "Cog" build.
>>
>> The "Stack" build continues to work fine for me.
>>
>> Since early april there is in the following file the following definition :
>>
>> platforms/Cross/vm/sq.h
>>
>> #       define getReturnAddress()
>> __builtin_extract_return_addr(__builtin_return_address(0))
>>
>> Eliot Miranda wrote in the thread:
>>
>> http://forum.world.st/Broken-5-3-downloads-need-fixing-td5115132.html
>>
>> "Things are pretty stable. There was one major change to how the VM moves
>> from machine code into the interpreter, replacing a setjmp/longjmp pair
>> with a much lighter-weight "jump-call with substituted return address". But
>> this "just works".  We're able to perform experments without disturbinf=g
>> trunk.  SO for example, adding makefiles to allow building of the VM under
>> clang-cl.exe on Windows was done without affecting the other builds at all."
>>
>> Is there a compiler flag (#define) to re-enable the old code with
>> setjmp/longjmp ?
>>
>> Or is there code in the 'platforms/Cross/vm/sqCog*' files
>> that could help to implement the required function for 'return address',
>> if that is not provided by the compiler ... ?
>>
>> I am hoping to re-enable the old setjmp/longjmp code.
>>
>> Also note that this may be useful for other users as well,
>> to be able to 'revert' to the legacy old code.
>>
> 
> Nah, it's trivial to implement.  The new scheme is much cheaper and hence
> faster than setjmp/longjmp.  So I'd much rather spread it further than
> support two versions.  The compiler supports gcc's inline extended
> assembler right?  In a normal frame on x86/x86_64 the frame pointer points
> to the word below the return address, so would look like this:
> 
> #if __GNUC__ || __clang__
> # if defined(_X86_) || defined(i386) || defined(__i386) || defined(__i386__)
> #   define getretaddr() ({ register usqIntptr_t retpc;                  \
>                      asm volatile ("movl 4(%%ebp),%0" : "=r"(retpc) : ); \
>                      retpc; })
> # elif defined(x86_64) || defined(__x86_64) || defined(__x86_64__) ||
> defined(__amd64) || defined(__amd64__) || defined(x64) || defined(_M_AMD64)
>|| defined(_M_X64) || defined(_M_IA64)
> #   define getretaddr() ({ register usqIntptr_t retpc;                  \
>                      asm volatile ("movl 8(%%rbp),%0" : "=r"(retpc) : ); \
>                      retpc; })
> #endif
> 
> To make this convenient we need to decide whether to put it in
> sqPlatformSpecific.h (easy) or to perhaps
> rename platforms/Cross/vm/sqCogStackAlignment.h
> to platforms/Cross/vm/sqCogStackAccess.h and put it there.  That feels
> better than putting it in sq.h.  But in any case can you try adding the
> above definitions to the relevant sqPlatformSpecific.h?
> 
> 
> 
>> Regards,
>> David Stes
>>
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> 
> 
> --
> _,,,^..^,,,_
> best, Eliot