I've figured out what the problem is. The problem in my code was caused by
the fact that this ELF/DWARF file has so many compile units, whereas my
other examples have far fewer compile units. I'll try to explain what my
mistake was:
Task: Looking for the function declaration file/line, for an executable
address
Original Solution (pseudocode):
new DWARF Reader
for every ENTRY
if ENTRY is compile unit
initialise new LINEREADER
if ENTRY is SUBPROGRAM or INLINEDSUBROUTINE
if ADDRESS is in range of ENTRY
if has ABSTRACT ORIGIN tag
seek ABSTRACT offset <--- this is where the bug is
look up DECL FILE and DECL LINE using LINEREADER
The issue was caused when following the abstract origin. In this ELF/DWARF
file, it is likely that the entry is in a different compile unit, meaning
that the line reader is referring to the wrong line table.
With a bit more care, I'm now using the correct line reader and the problem
no longer occurs.
Thanks for the help.
On Sunday, February 13, 2022 at 10:59:44 PM UTC stephen.t....@gmail.com
wrote:
> Okay. I've attached a text file showing the results of "readelf --debug".
> The ELF file itself was produced by GCC 10.3.1, part of the toolchain
> distributed by ARM.
>
> These are the dwarf.Entry instances as output from my Go program, that are
> out of range for the result of LineReader.Files()
>
> &dwarf.Entry{Offset:0x37a1, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName, Val:"clearBuffer",
> Class:dwarf.ClassString}, dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclLine, Val:426,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrPrototyped,
> Val:true, Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrSibling,
> Val:0x37c9, Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x3767, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName,
> Val:"ColourConvert", Class:dwarf.ClassString},
> dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclLine, Val:462, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:15, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrPrototyped, Val:true, Class:dwarf.ClassFlag},
> dwarf.Field{Attr:dwarf.AttrType, Val:0x230f, Class:dwarf.ClassReference},
> dwarf.Field{Attr:dwarf.AttrSibling, Val:0x3786,
> Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x3228, Tag:dwarf.TagSubprogram, Children:false,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName,
> Val:"processAnimationCommand", Class:dwarf.ClassString},
> dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclLine, Val:1492, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6, Class:dwarf.ClassConstant}}}
>
> &dwarf.Entry{Offset:0x3690, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName, Val:"InitGameX",
> Class:dwarf.ClassString}, dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclLine, Val:567,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrSibling, Val:0x36f4,
> Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x3786, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName,
> Val:"setVideoBufferPointers", Class:dwarf.ClassString},
> dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclLine, Val:437, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrSibling, Val:0x37a1,
> Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x3204, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName,
> Val:"setAnimation", Class:dwarf.ClassString},
> dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclLine, Val:1544, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrPrototyped, Val:true, Class:dwarf.ClassFlag},
> dwarf.Field{Attr:dwarf.AttrSibling, Val:0x321f,
> Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x3664, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName, Val:"Initialize",
> Class:dwarf.ClassString}, dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclLine, Val:688,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrSibling, Val:0x3690,
> Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x375a, Tag:dwarf.TagSubprogram, Children:false,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName, Val:"main",
> Class:dwarf.ClassString}, dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclLine, Val:490,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:5,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrType, Val:0x2327,
> Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x35f8, Tag:dwarf.TagSubprogram, Children:false,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName,
> Val:"InitGameDatastreams", Class:dwarf.ClassString},
> dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclLine, Val:797, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6, Class:dwarf.ClassConstant}}}
>
> &dwarf.Entry{Offset:0x34f4, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName,
> Val:"GameScheduleAnimate", Class:dwarf.ClassString},
> dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclLine, Val:1077, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6, Class:dwarf.ClassConstant},
> dwarf.Field{Attr:dwarf.AttrSibling, Val:0x352d,
> Class:dwarf.ClassReference}}}
>
> &dwarf.Entry{Offset:0x3601, Tag:dwarf.TagSubprogram, Children:true,
> Field:[]dwarf.Field{dwarf.Field{Attr:dwarf.AttrExternal, Val:true,
> Class:dwarf.ClassFlag}, dwarf.Field{Attr:dwarf.AttrName, Val:"Scheduler",
> Class:dwarf.ClassString}, dwarf.Field{Attr:dwarf.AttrDeclFile, Val:10,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclLine, Val:753,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrDeclColumn, Val:6,
> Class:dwarf.ClassConstant}, dwarf.Field{Attr:dwarf.AttrSibling, Val:0x3629,
> Class:dwarf.ClassReference}}}
>
>
>
>
> On Sun, Feb 13, 2022 at 10:26 PM Ian Lance Taylor <ia...@golang.org>
> wrote:
>
>> On Sun, Feb 13, 2022 at 1:43 PM stephen.t....@gmail.com
>> <stephen.t....@gmail.com> wrote:
>> >
>> > I've encountered something else that I don't understand. This time
>> regarding dwarf.AttrDeclFile and how the value of that field relates to the
>> list of source files in the project
>> >
>> > From what I can understand, the value of AttrDeclFile is an index into
>> an array of filenames. If the number is zero then the indicates that no
>> source file has been specified.
>> >
>> > The dwarf package allows retrieval of the file list with
>> LineReader.Files() function - the LineReader being created with reference
>> to the current compilation unit.
>> >
>> > For most ELF/DWARF examples I have, my understanding seems correct.
>> However, in one example I have, the value of AttrDeclFile can exceed the
>> length of the file array returned by LineReader.Files(). An invalid
>> reference in other words.
>> >
>> > Moreover, for AttrDeclFiles values that are within range of the array,
>> they are most definitely referencing the wrong file.
>> >
>> > I'm I misunderstanding the relationship between AttrDeclFile and
>> LineReader.Files(), is there some other way of accessing the file array, or
>> has something gone horribly wrong?
>>
>> What you write sounds correct. Can you show us the output "readelf
>> --debug" on the file in question, and point out the problematic case?
>> Thanks.
>>
>> Ian
>>
>
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