[LLVMdev] [Debug Info PATCH] for support of ref_addr and removal of DIE duplication
Manman Ren
manman.ren at gmail.com
Mon Oct 14 11:44:56 PDT 2013
BTW, the worklist code could be used to decide among ref1, ref2, ref4 etc
if we want to reduce dwarf size.
There are some issues we need to fix before actually deciding among ref1,
ref2, and ref4:
Since the Abbreviation depends on the reference form, we can assign
Abbreviation for a DIE after the reference form is decided,
but we can decide on the reference form only after we know the offsets of
each DIE (the offset depends on the encoded size of AbbrevNumber, which is
encoded with ULEB128).
So it may not work out, just a thought,
Manman
On Fri, Oct 11, 2013 at 4:41 PM, David Blaikie <dblaikie at gmail.com> wrote:
> The first patch seems fine, though the comment on the modified addDIEEntry
> function is a bit confusing:
>
> -/// addDIEEntry - Add a DIE attribute data and value.
> +/// addDIEEntry - Add a DIE attribute data and value. The form should be
> +/// a reference form: ref1, ref2, ref4, ref8, ref_udata, ref_addr,
> +/// or ref_sig8. A form can be chosen inside addDIEEntry.
>
> When the comment says "The form should be" - it sounds like it /could/ be
> something else, etc. As though the caller would specify it and must meet
> some requirement. But the caller doesn't specify it at all. I'd probably
> leave the comment out entirely - as the form isn't specified at the caller,
> it must be chosen by the callee.
>
> As a comparison, "addFlag" doesn't take a form, but it doesn't document
> that the form may be _flag or _flag_present - that's just an implementation
> detail.
>
> So in short, I would suggest you not modify the comment at all (leave it
> as it is today) - with that, please commit this patch.
>
> Did you find a test case for the worklist code yet?
>
>
> On Fri, Oct 11, 2013 at 4:35 PM, Manman Ren <manman.ren at gmail.com> wrote:
>
>>
>> Ping :)
>>
>>
>>
>> On Wed, Oct 9, 2013 at 5:22 PM, Manman Ren <manman.ren at gmail.com> wrote:
>>
>>>
>>>
>>>
>>> On Wed, Oct 9, 2013 at 1:32 PM, Manman Ren <manman.ren at gmail.com> wrote:
>>>
>>>>
>>>> David,
>>>>
>>>> Thanks for reviewing!
>>>>
>>>> On Wed, Oct 9, 2013 at 11:36 AM, David Blaikie <dblaikie at gmail.com>wrote:
>>>>
>>>>> Might be easier if these were on Phabricator, but here are some
>>>>> thoughts:
>>>>>
>>>>> 0001:
>>>>> This patch generally, while separated for legibility, is untested &
>>>>> difficult to discuss in isolation.
>>>>>
>>>> I agree, this patch adds the functionality but does not use it, the 2nd
>>>> patch uses ref_addr.
>>>> If you think I should merge the two and commit as a single patch, let
>>>> me know.
>>>>
>>>>
>>>>> I may need to refer to the second patch in reviewing this first one.
>>>>> DwarfDebug.cpp:
>>>>> computeSizeAndOffsets:
>>>>> I believe this produces the wrong offset for the 3rd CU and
>>>>> onwards. computeSizeAndOffset returns the EndOffset which is absolute, not
>>>>> relative to the Offset passed in, so it should be assigned to SecOffset,
>>>>> not added to it. (eg: if you have CUs at 0, 42, and 57 - the first pass
>>>>> through SecOffset will be zero, then it'll be 0 + 42, then on the 3rd it'll
>>>>> be (0 + 42) + 57 which isn't right, it should just be 57). Please add more
>>>>> test coverage while fixing this issue.
>>>>>
>>>>
>>>> computeSizeAndOffset takes an offset that is relative to the start of
>>>> the CU and returns the offset relative to the CU after laying out the DIE.
>>>> The initial offset before laying out the CU DIE is the header size,
>>>> EndOffset will be the offset relative to the CU after laying out the whole
>>>> CU DIE.
>>>> We can think of EndOffset as the size of the whole CU DIE. SecOffset is
>>>> the offset from the Debug Info section, so we can update it by adding the
>>>> CU size.
>>>>
>>>> // Offset from the beginning of debug info section.
>>>> unsigned SecOffset = 0;
>>>> for (SmallVectorImpl<CompileUnit *>::iterator I = CUs.begin(),
>>>> E = CUs.end(); I != E; ++I) {
>>>> (*I)->setDebugInfoOffset(SecOffset);
>>>> unsigned Offset =
>>>> sizeof(int32_t) + // Length of Compilation Unit Info
>>>> sizeof(int16_t) + // DWARF version number
>>>> sizeof(int32_t) + // Offset Into Abbrev. Section
>>>> sizeof(int8_t); // Pointer Size (in bytes)
>>>>
>>>> unsigned EndOffset = computeSizeAndOffset((*I)->getCUDie(), Offset);
>>>> SecOffset += EndOffset;
>>>> }
>>>>
>>>
>>> Added more comments in attached patch.
>>>
>>>
>>>>
>>>>
>>>>> Eric/Manman: rough design question: compute the absolute offset of
>>>>> each CU within the debug_info section and describe them all relative to a
>>>>> single symbol at the start of the debug_info section, or should we put a
>>>>> label at the start of each CU?
>>>>>
>>>>
>>>> Either way should work. But since we already have the section offset
>>>> for each CU, describing relative to the start of debug_info section saves
>>>> us a few symbols :)
>>>>
>>>>
>>>>>
>>>>> 0002:
>>>>> ref_addr_relocation.ll:
>>>>> seems a bit vague in terms of how you test for the relocation. I
>>>>> think it'd make more sense to test the assembly, than the reafobj output,
>>>>> that way you can test that the correct bytes have the relocation rather
>>>>> than just that there's "some" .debug_info relocation in the file. For an
>>>>> example, see test/DebugInfo/X86/tls.ll I wrote - it has some "unannotated"
>>>>> bytes because we still don't have a nice way to annotate location bytes
>>>>> that are DWARF expressions, but it's close - I guess those should be
>>>>> CHECK-NEXTs, though. In any case, you should be able to check a few lines
>>>>> of assembly with the # DW_AT/DW_TAG annotation comments.
>>>>>
>>>>
>>>> I can check for ".quad .Lsection_info+38 #DW_AT_type".
>>>>
>>> Done in attached patch.
>>>
>>>>
>>>>
>>>>> You'd need to add the tu3.cpp from my example if you want to
>>>>> demonstrate that the relocation is actually working as intended and
>>>>> avoiding the bogus result I showed.
>>>>> type-unique-simple-a.ll
>>>>> While I agree that having common test cases helps reduce the
>>>>> number of separate invocations we have, this test case seems like it might
>>>>> be becoming a little hard to follow what's under test. Just going from the
>>>>> diff I'm not sure what's what. Could you give a brief description of the
>>>>> state of type-unique-simple2 files? What's involved? What's it meant to
>>>>> test? What's it actually testing?
>>>>>
>>>> I can add more comments. The source files are included in the testing
>>>> case. I am checking that llvm-link only generates a single copy of the
>>>> struct and the backend generates a single DIE and uses ref_addr.
>>>> The changes are to check "the backend generates a single DIE and uses
>>>> ref_addr".
>>>>
>>> Done in attached patch.
>>>
>>>>
>>>> DIE.h:
>>>>> checkCompileUnit could probably be called "getCompileUnitOrNull",
>>>>> the name "check*" seems to imply that it does some checking, which isn't
>>>>> true.
>>>>>
>>>> Will do.
>>>>
>>> Done in attached patch.
>>>
>>>>
>>>>
>>>>> DwarfCompileUnit.cpp:
>>>>> the "istype || issubprogram" check should probably be pulled out
>>>>> into a separate function, something like "isShareableAcrossCUs" or
>>>>> something like that (please, that's not the best name, let's discuss it
>>>>> further before we settle on a name) so that getDIE and insertDIE are sure
>>>>> to use the same test at all times.
>>>>>
>>>> Yes, the condition is shared between getDIE and insertDIE. I like
>>>> isSharableAcrossCUs, because that is why the map is in DwarfDebug instead
>>>> of CompileUnit.
>>>>
>>> Done in attached patch.
>>>
>>>>
>>>>
>>>>> Why does addDIEEntry take a form? When does the caller get to
>>>>> choose the form rather than the callee deciding between ref4 and ref_addr
>>>>> based on context?
>>>>>
>>>>
>>>> addDIEEntry took a form before my change and I didn't check why it did.
>>>> I will check if all callers always use ref4, if it it true, I will
>>>> submit a cleanup patch first.
>>>>
>>> Done in attached patch.
>>>
>>>>
>>>> I'm still unsure about this worklist thing - do your current tests
>>>>> cover the need for the worklist? ie: if we removed that logic, would tests
>>>>> fail? Can you describe a specific sequence where the worklist is necessary?
>>>>>
>>>>
>>>> If we are sure that DIEs are always added to an owner before calling
>>>> addDIEEntry, we don't need the worklist.
>>>> But I saw cases where that was not true, I will get a reduced testing
>>>> case.
>>>>
>>>
>>> If we try to assert both DIEs have owner in addDIEEntry, the following
>>> testing cases will fail:
>>> LLVM :: DebugInfo/X86/multiple-aranges.ll
>>> LLVM :: DebugInfo/X86/ref_addr_relocation.ll
>>> LLVM :: DebugInfo/X86/stmt-list-multiple-compile-units.ll
>>> LLVM :: DebugInfo/two-cus-from-same-file.ll
>>> LLVM :: Linker/type-unique-simple-a.ll
>>> LLVM :: Linker/type-unique-simple2.ll
>>>
>>> For ref_addr_relocation, it failed in
>>> #5 0x0000000100b169ba in llvm::DwarfDebug::addDIEEntry
>>> (this=0x103023600, Die=0x102e14090, Attribute=73, Entry=0x10302a9d0) at
>>> /Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp:3071
>>> #6 0x0000000100b040e0 in llvm::CompileUnit::addType (this=0x102e13ec0,
>>> Entity=0x102e14090, Ty={<llvm::DIScope> = {<llvm::DIDescriptor> = {DbgNode
>>> = 0x102e05f30}, <No data fields>}, <No data fields>}, Attribute=73) at
>>> /Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:910
>>> #7 0x0000000100b05bff in llvm::CompileUnit::createGlobalVariableDIE
>>> (this=0x102e13ec0, N=0x102e068c0) at
>>> /Users/manmanren/llvm_git/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:1505
>>>
>>> If we look at DwarfCompileUnit.cpp:
>>> VariableDIE = new DIE(GV.getTag());
>>> // Add to map.
>>> insertDIE(N, VariableDIE);
>>>
>>> // Add name and type.
>>> addString(VariableDIE, dwarf::DW_AT_name, GV.getDisplayName());
>>> addType(VariableDIE, GTy);
>>>
>>> The VariableDIE is not added to an owner yet when calling addType.
>>>
>>> Thanks,
>>> Manman
>>>
>>>
>>>
>>>
>>>> Manman
>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Oct 9, 2013 at 10:45 AM, Manman Ren <manman.ren at gmail.com>wrote:
>>>>>
>>>>>>
>>>>>> Ping
>>>>>>
>>>>>> -Manman
>>>>>>
>>>>>>
>>>>>> On Fri, Oct 4, 2013 at 7:00 PM, Manman Ren <manman.ren at gmail.com>wrote:
>>>>>>
>>>>>>>
>>>>>>> Hi All,
>>>>>>>
>>>>>>> The first patch adds support for ref_addr.
>>>>>>> Most of it is from r176882, but instead of always using an integer
>>>>>>> for ref_addr, we use label + offset for relocation on non-darwin platforms.
>>>>>>>
>>>>>>> The second patch is a modified version of r191792.
>>>>>>> The main change is to use a single map instead of 3 maps in
>>>>>>> DwarfDebug and instead of calling DwarfDebug::getDIE|insertDIE directly, we
>>>>>>> delegate the function calls to DwarfDebug from CompileUnit.
>>>>>>>
>>>>>>> No testing case is added in the 1st patch, since the compiler does
>>>>>>> not use ref_addr yet.
>>>>>>>
>>>>>>> For the 2nd patch, testing cases are updated to make sure we remove
>>>>>>> duplicated DIEs and use ref_addr to refer to the type DIE. A testing case
>>>>>>> is also added to make sure we generate a relocation entry for ref_addr on
>>>>>>> linux platform.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Manman
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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