llvm dev - Oct 2013 - [LLVMdev] [Debug Info PATCH] for support of ref_addr and removal of DIE duplication

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 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.

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?

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.
    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?
  DIE.h:
    checkCompileUnit could probably be called "getCompileUnitOrNull",
the
name "check*" seems to imply that it does some checking, which
isn't true.
  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.
  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?
  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?



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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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;
  }

> 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".

>     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".

  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.

>   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.

>   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.

  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.

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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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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