[llvm] r246406 - [dsymutil] Fix handling of inlined_subprogram low_pcs
David Blaikie via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 8 12:24:55 PDT 2015
On Mon, Aug 31, 2015 at 11:10 AM, Frédéric Riss <friss at apple.com> wrote:
>
> On Aug 31, 2015, at 9:07 AM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Mon, Aug 31, 2015 at 9:05 AM, David Blaikie <dblaikie at gmail.com> wrote:
>
>>
>>
>> On Sun, Aug 30, 2015 at 6:43 PM, Frederic Riss via llvm-commits <
>> llvm-commits at lists.llvm.org> wrote:
>>
>>> Author: friss
>>> Date: Sun Aug 30 20:43:14 2015
>>> New Revision: 246406
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=246406&view=rev
>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D246406-26view-3Drev&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=_sX2G1Du1KZyzi5BD4_ddw&m=FkrVlXa3-EdUHEUklJrpTIxLR2zDdr3ysgnj0hyNiNc&s=-yp_b9w-sonxhFICg6npPkz6_FLOw29qR_X8EIzjwWY&e=>
>>> Log:
>>> [dsymutil] Fix handling of inlined_subprogram low_pcs
>>>
>>> The value of an inlined subprogram low_pc attribute should not
>>> get relocated, but it can happen that it matches the enclosing
>>> function's start address and thus gets the generic treatment.
>>> Special case it to avoid applying the PC offset twice.
>>>
>>
>> I'm a tad confused - do you store the low_pcs as offsets relative to the
>> function
>>
>
> (sorry, bouncy shuttle to work & accidentally sent before I finished that
> sentence...)
>
> do you store the low_pcs as offsets relative to the function's low_pc?
> That's interesting - and perhaps something we should standardize/generalize
> to reduce relocations in all our DWARF output (but I don't think there's
> any standard for it yet in DWARF), but I'm not sure why that would require
> special casing the case where the two low_pcs are equal - wouldn't that
> just mean the low_pc of the inlined subroutine would be at zero offset from
> the subprogram's low_pc? (& still not relocated)
>
>
> dsymutil takes the debug map as input that only contains the function (and
> variables) start addresses. That’s the only thing we can count on being
> exact. We then do a pass over all the debug_info relocations to find the
> ones that correspond to those addresses (and the DIEs where we find the
> ‘interesting’ relocations are the ones that define which part of the DIE
> tree we keep). Then — once we decided what to keep — we go over the kept
> DIEs and we clone them, applying the relocations in the process. But note
> that the relocations we’ve chosen are only for the entry points, thus we
> need to have the code around to handle the
> lexical_block/inlined_subroutine, and this code doesn’t use the relocations
> (it applies an offset that we computed when handling the subprogram DIE).
>
> What happened here is that the generic code that applied the relocations
> would also patch the inlined_subroutine low_pc because the relocation was
> the same as the entry point. And then the code handling the low_pc
> attributes for the inlined_subroutine would apply the offset a second time.
>
OK - what I'm wondering is whether it would work better/as well to
generalize this code, rather than two distinct passes/processes. low_pc
should just be a zero-offset relocation, right?
Maybe I'm not understanding/explaining very well, though.
> We might be able to completely remove any specific handling and just
> ‘promote’ all the relocations that fall inside a linked function as
> interesting. At the point we do that triaging relocs, we are not exploring
> the DIE tree though, just looking at the relocation list, so it would
> require us to trust the size field of the debug map, and I’m not sure we
> can do that 100% of the time (I know that this field is not accurate, it’s
> usually too big because it factors in alignment, but that might not be an
> issue if nothing gets allocated in the alignment padding).
>
Hmm - not sure I follow this. You're suggesting that if a non-debug-aware
tool applied the relocations in the object file/debug info, it would
mangle/damage the debug info?
- David
>
> Fred
>
>
>>
>>>
>>> Added:
>>> llvm/trunk/test/tools/dsymutil/ARM/dummy-debug-map-amr64.map
>>> llvm/trunk/test/tools/dsymutil/ARM/inlined-low_pc.c
>>> llvm/trunk/test/tools/dsymutil/Inputs/inlined-low_pc/
>>> llvm/trunk/test/tools/dsymutil/Inputs/inlined-low_pc/1.o
>>> Modified:
>>> llvm/trunk/test/tools/dsymutil/ARM/lit.local.cfg
>>> llvm/trunk/tools/dsymutil/DwarfLinker.cpp
>>>
>>> Added: llvm/trunk/test/tools/dsymutil/ARM/dummy-debug-map-amr64.map
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/dsymutil/ARM/dummy-debug-map-amr64.map?rev=246406&view=auto
>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_tools_dsymutil_ARM_dummy-2Ddebug-2Dmap-2Damr64.map-3Frev-3D246406-26view-3Dauto&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=_sX2G1Du1KZyzi5BD4_ddw&m=FkrVlXa3-EdUHEUklJrpTIxLR2zDdr3ysgnj0hyNiNc&s=Za5qJ6LsFqNTEnS7lR9nOUQu3xiakQs49dpO89XaJg0&e=>
>>>
>>> ==============================================================================
>>> --- llvm/trunk/test/tools/dsymutil/ARM/dummy-debug-map-amr64.map (added)
>>> +++ llvm/trunk/test/tools/dsymutil/ARM/dummy-debug-map-amr64.map Sun Aug
>>> 30 20:43:14 2015
>>> @@ -0,0 +1,15 @@
>>> +# This is a dummy debug map used for some tests where the contents of
>>> the
>>> +# map are just an implementation detail. The tests wanting to use that
>>> file
>>> +# should put all there object files in an explicitely named
>>> sub-directory
>>> +# of Inputs, and they should be named 1.o, 2.o, ...
>>> +# As not finding an object file or symbols isn't a fatal error for
>>> dsymutil,
>>> +# you can extend this file with as much object files and symbols as
>>> needed.
>>> +
>>> +---
>>> +triple: 'arm64-apple-darwin'
>>> +objects:
>>> + - filename: 1.o
>>> + symbols:
>>> + - { sym: _bar, objAddr: 0x0, binAddr: 0x10000, size: 0x10 }
>>> +...
>>> +
>>>
>>> Added: llvm/trunk/test/tools/dsymutil/ARM/inlined-low_pc.c
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/dsymutil/ARM/inlined-low_pc.c?rev=246406&view=auto
>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_tools_dsymutil_ARM_inlined-2Dlow-5Fpc.c-3Frev-3D246406-26view-3Dauto&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=_sX2G1Du1KZyzi5BD4_ddw&m=FkrVlXa3-EdUHEUklJrpTIxLR2zDdr3ysgnj0hyNiNc&s=Q8OeSlNX91218xjgr3aIrN1U1Bssvnu-Nu8WzoX_nlI&e=>
>>>
>>> ==============================================================================
>>> --- llvm/trunk/test/tools/dsymutil/ARM/inlined-low_pc.c (added)
>>> +++ llvm/trunk/test/tools/dsymutil/ARM/inlined-low_pc.c Sun Aug 30
>>> 20:43:14 2015
>>> @@ -0,0 +1,15 @@
>>> +/* Compiled with: clang -arch=arm64 -O2 -g -c inlined_low_pc.c */
>>> +
>>> +static int foo(int i) { return 42 + i; }
>>> +int bar(int a) { return foo(a); }
>>> +
>>> +// RUN: llvm-dsymutil -f -y %p/dummy-debug-map-amr64.map
>>> -oso-prepend-path %p/../Inputs/inlined-low_pc -o - | llvm-dwarfdump - |
>>> FileCheck %s
>>> +
>>> +// CHECK: DW_TAG_subprogram
>>> +// CHECK: DW_AT_low_pc{{.*}}0x0000000000010000
>>> +// CHECK: DW_AT_name{{.*}}"bar"
>>> +// CHECK-NOT: NULL
>>> +// CHECK: DW_TAG_inlined_subroutine
>>> +// CHECK-NEXT: DW_AT_abstract_origin{{.*}}"foo"
>>> +// CHECK-NEXT: DW_AT_low_pc{{.*}}0x0000000000010000
>>> +
>>>
>>> Modified: llvm/trunk/test/tools/dsymutil/ARM/lit.local.cfg
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/dsymutil/ARM/lit.local.cfg?rev=246406&r1=246405&r2=246406&view=diff
>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_tools_dsymutil_ARM_lit.local.cfg-3Frev-3D246406-26r1-3D246405-26r2-3D246406-26view-3Ddiff&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=_sX2G1Du1KZyzi5BD4_ddw&m=FkrVlXa3-EdUHEUklJrpTIxLR2zDdr3ysgnj0hyNiNc&s=zEAxxhhWFPrzEd5HWOml9qsDlLRCwN45LHyqj9f5wUc&e=>
>>>
>>> ==============================================================================
>>> --- llvm/trunk/test/tools/dsymutil/ARM/lit.local.cfg (original)
>>> +++ llvm/trunk/test/tools/dsymutil/ARM/lit.local.cfg Sun Aug 30 20:43:14
>>> 2015
>>> @@ -2,3 +2,6 @@ if not 'ARM' in config.root.targets:
>>> config.unsupported = True
>>> if not 'AArch64' in config.root.targets:
>>> config.unsupported = True
>>> +
>>> +config.suffixes = ['.test', '.cpp', '.c']
>>> +
>>>
>>> Added: llvm/trunk/test/tools/dsymutil/Inputs/inlined-low_pc/1.o
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/dsymutil/Inputs/inlined-low_pc/1.o?rev=246406&view=auto
>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_tools_dsymutil_Inputs_inlined-2Dlow-5Fpc_1.o-3Frev-3D246406-26view-3Dauto&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=_sX2G1Du1KZyzi5BD4_ddw&m=FkrVlXa3-EdUHEUklJrpTIxLR2zDdr3ysgnj0hyNiNc&s=lY2aOkTZ45aHfHwE3xL8Amnff5hUDIrveaBrWrrNdnI&e=>
>>>
>>> ==============================================================================
>>> Binary files llvm/trunk/test/tools/dsymutil/Inputs/inlined-low_pc/1.o
>>> (added) and llvm/trunk/test/tools/dsymutil/Inputs/inlined-low_pc/1.o Sun
>>> Aug 30 20:43:14 2015 differ
>>>
>>> Modified: llvm/trunk/tools/dsymutil/DwarfLinker.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/dsymutil/DwarfLinker.cpp?rev=246406&r1=246405&r2=246406&view=diff
>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_tools_dsymutil_DwarfLinker.cpp-3Frev-3D246406-26r1-3D246405-26r2-3D246406-26view-3Ddiff&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=_sX2G1Du1KZyzi5BD4_ddw&m=FkrVlXa3-EdUHEUklJrpTIxLR2zDdr3ysgnj0hyNiNc&s=6xjIRngxynhJS54wLMKfMmHyjNR49UDteCNLX-SlUxI&e=>
>>>
>>> ==============================================================================
>>> --- llvm/trunk/tools/dsymutil/DwarfLinker.cpp (original)
>>> +++ llvm/trunk/tools/dsymutil/DwarfLinker.cpp Sun Aug 30 20:43:14 2015
>>> @@ -1206,6 +1206,7 @@ private:
>>> const char *Name, *MangledName; ///< Names.
>>> uint32_t NameOffset, MangledNameOffset; ///< Offsets in the string
>>> pool.
>>>
>>> + uint64_t OrigLowPc; ///< Value of AT_low_pc in the input DIE
>>> uint64_t OrigHighPc; ///< Value of AT_high_pc in the input DIE
>>> int64_t PCOffset; ///< Offset to apply to PC addresses inside a
>>> function.
>>>
>>> @@ -1214,8 +1215,8 @@ private:
>>>
>>> AttributesInfo()
>>> : Name(nullptr), MangledName(nullptr), NameOffset(0),
>>> - MangledNameOffset(0), OrigHighPc(0), PCOffset(0),
>>> HasLowPc(false),
>>> - IsDeclaration(false) {}
>>> + MangledNameOffset(0), OrigLowPc(UINT64_MAX), OrigHighPc(0),
>>> + PCOffset(0), HasLowPc(false), IsDeclaration(false) {}
>>> };
>>>
>>> /// \brief Helper for cloneDIE.
>>> @@ -2274,7 +2275,12 @@ unsigned DwarfLinker::cloneAddressAttrib
>>> if (AttrSpec.Attr == dwarf::DW_AT_low_pc) {
>>> if (Die.getTag() == dwarf::DW_TAG_inlined_subroutine ||
>>> Die.getTag() == dwarf::DW_TAG_lexical_block)
>>> - Addr += Info.PCOffset;
>>> + // The low_pc of a block or inline subroutine might get
>>> + // relocated because it happens to match the low_pc of the
>>> + // enclosing subprogram. To prevent issues with that, always use
>>> + // the low_pc from the input DIE if relocations have been applied.
>>> + Addr = (Info.OrigLowPc != UINT64_MAX ? Info.OrigLowPc : Addr) +
>>> + Info.PCOffset;
>>> else if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
>>> Addr = Unit.getLowPc();
>>> if (Addr == UINT64_MAX)
>>> @@ -2522,6 +2528,11 @@ DIE *DwarfLinker::cloneDIE(const DWARFDe
>>> // high_pc value is done in cloneAddressAttribute().
>>> AttrInfo.OrigHighPc =
>>> InputDIE.getAttributeValueAsAddress(&U, dwarf::DW_AT_high_pc,
>>> 0);
>>> + // Also store the low_pc. It might get relocated in an
>>> + // inline_subprogram that happens at the beginning of its
>>> + // inlining function.
>>> + AttrInfo.OrigLowPc =
>>> + InputDIE.getAttributeValueAsAddress(&U, dwarf::DW_AT_low_pc,
>>> UINT64_MAX);
>>> }
>>>
>>> // Reset the Offset to 0 as we will be working on the local copy of
>>>
>>>
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>>>
>>
>>
>
>
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