On 03/06/2018 10:37 AM, Roman Popov wrote:
Hi everyone,
I'm working on a dynamic analysis tool that needs runtime reflection in
C++. Since C++ has no standardized runtime reflection, I'm using DWARF
as a source of reflection metadata.
Is it a legitimate use-case from DWARF standard point of view?
It is certainly an interesting use case. I haven't see this done
before, but since DWARF gives descriptions of classes, it seems
reasonable.
It has been working great for me until I've upgraded to latest g++ and
clang compilers. Those compilers produce ambiguous names for some
template instantiations, so my tools no longer work. So I start to
wonder: whether it me misusing DWARF, or it is compilers that are buggy.
In particular, what is the DWARF answer for these questions:
1. Does DWARF guarantees that:
typeid(T1) == typeid(T2) ==> DW_AT_name(T1) == DW_AT_name(T2)
typeid(T1) != typeid(T2) ==> DW_AT_name(T1) != DW_AT_name(T2)
i.e. Is DW_AT_name an unique identifier for type?
The AT_name is the declared name of the type in the source, not the name
of an underlying type. For example, if your source is
typedef int int_name_1;
typedef int int_name_2;
int_name_1 name_1;
int_name_2 name_2;
The (edited) DWARF for this
<1d>: (DW_TAG_typedef)
<1e> DW_AT_name : int_name_1
<24> DW_AT_type : <0x28>
<28>: (DW_TAG_base_type)
<2b> DW_AT_name : int
<2f>: (DW_TAG_typedef)
<30> DW_AT_name : int_name_2
<36> DW_AT_type : <0x28>
<3a>: (DW_TAG_variable)
<3b> DW_AT_name : name_1
<41> DW_AT_type : <0x1d>
<4f>: (DW_TAG_variable)
<50> DW_AT_name : name_2
<56> DW_AT_type : <0x2f>
typeid(name_1) == typeid(name_2) == "int" which is different from
AT_name(name_1) or AT_name(name_2).
2. Does DWARF guarantees that DW_AT_name(T) is a valid source language
name?
Yes, assuming that the compiler generates a valid source type. In some
cases, particularly with template classes, this may not be the case.
i.e. If I copy string from DW_AT_name to source code, and compile it
with the same compiler that produced DWARF, will it produce the same type?
T var1;
DW_AT_name(T) var2;
typeid(var1) == typeid (var2) ?
I expect that it would.
--
Michael Eager ea...@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306
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