[llvm] r246406 - [dsymutil] Fix handling of inlined_subprogram low_pcs

Mon Aug 31 09:07:37 PDT 2015

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
>> 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)

>
>
>>
>> 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
>>
>> ==============================================================================
>> --- 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
>>
>> ==============================================================================
>> --- 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
>>
>> ==============================================================================
>> --- 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
>>
>> ==============================================================================
>> 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
>>
>> ==============================================================================
>> --- 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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