[webkit-dev] want to port JIT to MIPS - patchImmediate
Zoltan Herczeg
zherczeg at inf.u-szeged.hu
Thu Feb 26 14:03:55 PST 2009
Hi,
jit GetByIdSelf methods caches the structure ID (see the line starting
with Jump structureCheck = ...) and the offset in the PropertyStorage (see
DataLabel32 displacementLabel = ...) in the jit code itself. StructureID-s
are required to check that the input JSValue is the same JSObject which
was used to set up the property offset.
Things are more complicated for structures, which have multiple structure
ID-s (called prototype chain). A separate stub function is generated for
each of those objects, and the head is called after the main
structureCheck fail.
get_by_id:
[...]
[structure check] -> on fail goto first_stub_function
label_ok:
load cached value
label_exit:
Somewhere else in the memory:
first_stub_function:
[structure or prototaype chain check] -> on fail goto second_stub_function
load cached value
goto label_exit
second_stub_function:
[same thing again]
Currently, the maximum number of extra stub functions is 4. If all of them
fails, a get_by_id_generic function is called. To insert a new stub
function, you need to keep the address of the first [structure check], and
repatch it after a new head is added. Implementing these features was much
more complicated for ARM. I hope mips is not so different compared to x86.
Cheers,
Zoltan
> Hi,
> in jitPropertyAccess.cpp:
> // Patch the offset into the propoerty map to load from, then patch the
> Structure to look for...
> stubInfo->hotPathBegin.dataLabel32AtOffset(patchOffsetGetByIdPropertyMapOffset).repatch(cachedOffset
> * sizeof(JSValuePtr));
>
> how propertyMap is used and why we need such patch? who will/how to use
> patched data?
> rgds
> joe
>
> --- On Sun, 2/22/09, x yz <lastguy at yahoo.com> wrote:
>
>> From: x yz <lastguy at yahoo.com>
>> Subject: Re: [webkit-dev] want to port JIT to MIPS
>> To: "WebKit Development" <webkit-dev at lists.webkit.org>, "Gavin
>> Barraclough" <barraclough at apple.com>
>> Date: Sunday, February 22, 2009, 4:34 PM
>> Thanks a lot otherwise I have misunderstanding. Yes I'll
>> do wrec first. I just want to clean up possible blocking
>> issues.
>>
>> I see wrec uses regparm(3) and jit always use fastcall for
>> X86?
>> In JIT.cpp ctiTrampoline put CallFrame in edi, but how
>> about other arguments - where are they be fetched/poped from
>> stack?
>>
>> when deal with caller/callee saved regs, gcc MIPS just
>> preserves them when necesasary. The problem is after JIT
>> used gcc may not have enough knowledge on
>> "necessary", do we have a way to force gcc always
>> preserve
>> them?
>>
>> how to identify a patch (patchimm/patchptr/patchaddr)
>> relates to a data field in an instruction or relates to an
>> element in a data array? In Mips the former means the 32bit
>> needs to be separated into two 16bits and patched into two
>> instructions. But if a 32bit is a pointer in a pointer
>> array, we can save it directly.
>>
>> rgds
>> joe
>>
>>
>> --- On Fri, 2/20/09, Gavin Barraclough
>> <barraclough at apple.com> wrote:
>>
>> > From: Gavin Barraclough <barraclough at apple.com>
>> > Subject: Re: [webkit-dev] want to port JIT to MIPS
>> > To: "WebKit Development"
>> <webkit-dev at lists.webkit.org>
>> > Date: Friday, February 20, 2009, 2:01 PM
>> > On Feb 19, 2009, at 8:27 PM, x yz wrote:
>> >
>> > > I'd appreaciate your help to clarify the
>> problem I
>> > faced:
>> > >
>> > > 1.In JIT.cpp I roughly understand ctiTrampoline()
>> > except for sp-0x1C, I guess the 1C includes 6 argument
>> yet
>> > the 7th or 1st may be the hidden C++ pointer? And the
>> > reserved 1C stack space seems not used? why esi is
>> forced to
>> > be 512 rather than use input argument?
>> >
>> > The JIT allocates a fixed frame on the stack which is
>> used
>> > to pass arguments into stub functions. The 0x1C
>> contains a
>> > spare word or two to maintain stack alignment. %esi
>> is used
>> > in the timeout check mechanism.
>> >
>> > > 2.How to understand the stack balance in
>> > ctiVMThrowTrampoline()? why after calling we still add
>> 1C
>> > w/o sub 1C before calling? where comes
>> > _ZN3JSC11Interpreter12cti_vm_throwEPPv and how do I
>> know
>> > which name for Mips? does this one relates to variable
>> > argument function call?
>> >
>> > ctiVMThrowTrampoline is never called as a function (it
>> is
>> > declared as a function only to provide a symbol that
>> can be
>> > manipulated from C code). ctiVMThrowTrampoline is
>> used in
>> > returning back from JIT generated code, in the case of
>> an
>> > exception.
>> >
>> > > 3.I know how to handle jump in Mips, but not sure
>> > how/when to handle patchAddress/patchImm/patchPointer
>> > because I'm not sure the instructions related. I
>> guess
>> > all patches are for last 32bit IMM field of
>> instructions.
>> > > Mips can't load 32bit in one instruction,
>> thus I
>> > need to know the instruction before I can patch/add in
>> the
>> > 32bit data.
>> > >
>> > > 4.I'm kind of want no asm code outside
>> > <assembler> folder, any plan for that?
>> >
>> > No. The assembler is intended to be independent of
>> > JavaScript types - it's just an assembler. The
>> asm
>> > trampolines are specific to the JIT. It is currently
>> the
>> > intention that architecture specific parts of the JIT
>> > implementation will remain in the jit folder.
>> >
>> > I'd suggest that in attempting to port the jit,
>> WREC
>> > would be a good place to start.
>> >
>> > cheers,
>> > G.
>> >
>> > >
>> > > rgds
>> > > joe
>> > >
>> > > --- On Mon, 2/16/09, x yz
>> <lastguy at yahoo.com>
>> > wrote:
>> > >
>> > >> From: x yz <lastguy at yahoo.com>
>> > >> Subject: Re: [webkit-dev] want to port JIT to
>> MIPS
>> > - when WREC/JIT enabled?
>> > >> To: "Gavin Barraclough"
>> > <barraclough at apple.com>
>> > >> Cc: "WebKit Development"
>> > <webkit-dev at lists.webkit.org>
>> > >> Date: Monday, February 16, 2009, 5:25 AM
>> > >> Hi,
>> > >> from paltform.h it is enabled only on X86
>> MAC/WIN;
>> > from
>> > >> javaScriptCore.pri it is also enabled for
>> > (QT_ARCH,i386).
>> > >> But, from config.log I see them are enabled!
>> > >>
>> > >> how can I run WREC/JIT test so I can trace in
>> X86
>> > asm coce
>> > >> generated?
>> > >> thanks a lot.
>> > >> joe
>> > >>
>> > >>
>> > >>
>> > >> --- On Sat, 2/7/09, Gavin Barraclough
>> > >> <barraclough at apple.com> wrote:
>> > >>
>> > >>> From: Gavin Barraclough
>> > <barraclough at apple.com>
>> > >>> Subject: Re: [webkit-dev] want to port
>> JIT to
>> > MIPS -
>> > >> using X86::ecx as base
>> > >>> To: lastguy at yahoo.com
>> > >>> Cc: "WebKit Development"
>> > >> <webkit-dev at lists.webkit.org>
>> > >>> Date: Saturday, February 7, 2009, 7:08 AM
>> > >>> On Feb 6, 2009, at 2:52 PM, x yz wrote:
>> > >>>
>> > >>>> 1.what's the meaning of
>> > ALTERNATE_JSIMMEDIATE
>> > >> and
>> > >>> slow case?
>> > >>>
>> > >>> On x86-64 we use a different
>> implementation of
>> > the
>> > >> class
>> > >>> JSImmediate. See JSImmediate.h.
>> > >>> Re 'slow case', in the JIT code
>> > generation is
>> > >>> performed as two passes over the bytecode
>> –
>> > see
>> > >>> JIT::privateCompileMainPass and
>> > >>> JIT::privateCompileSlowCases.
>> > >>>
>> > >>>> 2.how come the following code can use
>> ECX
>> > as base
>> > >>> register?
>> > >>>> load32(Address(X86::ecx,
>> > FIELD_OFFSET(Structure,
>> > >>> m_typeInfo.m_flags)), X86::ecx);
>> > >>>> if the X86::ecx just means its value
>> 1 in
>> > ModR/M,
>> > >> does
>> > >>> it means [BX+DI]?
>> > >>>
>> > >>> I think you're looking at the old
>> 16-bit
>> > >> addressing
>> > >>> mode tables; 32/64-bit x86 can happily
>> encode
>> > ecx as a
>> > >> base
>> > >>> register. If you're looking at the
>> Intel
>> > IA-32
>> > >> manual
>> > >>> volume 2, see table 2-2 on the next page.
>> > >>>
>> > >>>> 3. can anybody help me on my previous
>> > questions?
>> > >> does
>> > >>> JIT support floating point?
>> > >>>
>> > >>> Yes, some. See JITArithmetic.cpp.
>> > >>>
>> > >>> cheers,
>> > >>> G.
>> > >>
>> > >>
>> > >>
>> > >>
>> _______________________________________________
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>> > >> webkit-dev at lists.webkit.org
>> > >>
>> >
>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>> > >
>> > >
>> > >
>> >
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>> >
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