[llvm-dev] Function name

[David Blaikie via llvm-dev]

On Fri, Oct 26, 2018 at 8:28 AM via llvm-dev <llvm-dev at lists.llvm.org>
wrote:

> Hi Muhui,
>
>
>
> I believe the names in the callgraph are the "mangled" name, which DWARF
> refers to as the linkage name.  This would be recorded in the
> DW_AT_MIPS_linkage_name or DW_AT_linkage_name attribute, depending on the
> version of DWARF.
>
>
>
> DW_AT_specification is a way to associate two DWARF entries for the same
> entity.  You will see this most commonly for inlined functions, where the
> DWARF entry for the inlined instance has a DW_AT_specification pointing to
> the "abstract" instance for the same function.
>

Minor thing: DW_AT_specification is used for decl/def separations rather
than inline/concrete/abstract (that uses abstract_origin). But similar
stuff, for sure.


>   This is intended as a space-saving tactic, as many of the attributes for
> a function (including its linkage name) are the same across all inlined
> instances.  The abstract instance has the common attributes, while the
> concrete instances have the attributes specific to each inlined instance
> (e.g., code ranges).
>
>
>
> As for the PLT segment, I suspect that DWARF does not describe these
> because they are artifacts of the ABI and do not reflect anything in the
> source.  The callgraph describes them because they are explicit in the IR.
>
> --paulr
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Muhui
> Jiang via llvm-dev
> *Sent:* Thursday, October 25, 2018 4:16 PM
> *To:* llvm-dev
> *Subject:* [llvm-dev] Function name
>
>
>
> Hi
>
>
>
> I refer to the binary generated by C++ code.
>
>
>
> I am curious about the name inside the callgraph, which is generated by
> the tool
>
>
>
> opt -dot-callgraph target.bc
>
>
>
> I found the names inside the callgraph follow the C++ function name rule.
> Then I would like to check the name inside the debugging information, which
> is generated by the command
>
>
>
> llvm-dwarfdump -debug-info target.o
>
>
>
> I manually checked it, I found sometimes the name(label in the callgraph)
> is the attribute of `DW_AT_specification`, sometimes is
> `DW_AT_MIPS_linkage_name`. Can anyone explain these? What should be the
> right function name inside the dwarf debugging information?
>

Yeah, llvm-dwarfdump prints the mangled/linkage name next to
DW_AT_specification for ease of reading, but in reality the specification
doesn't have the linkage name (it's pulling it from the DIE the
specification refers to) - use '-v' with llvm-dwarfdump to see the details
of how that's all wired up.


>
>
> Another question is about the PLT segment. I found that the callgraph will
> contain the functions inside the ELF PLT segment while the dwarf debugging
> information does not contain them. Could anyone explain these? Many Thanks
>
>
>
> Regards
>
> Muhui
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