> On Apr 19, 2018, at 9:44 AM, Greg Clayton via lldb-dev
> <[email protected]> wrote:
>
>
>
>> On Apr 19, 2018, at 6:51 AM, Zdenek Prikryl via lldb-dev
>> <[email protected]> wrote:
>>
>> Hi lldb developers,
>>
>> I've been researching using lldb + gdbserver stub that is based on Harvard
>> architecture with multiple address spaces (one program, multiple data). The
>> commonly adopted approach is that everything is mapped to a single "virtual"
>> address space. The stub reads/writes from/to the right memory based on the
>> "virtual" addresses. But I'd like to use real addresses with address space
>> id instead. So, I've started looking at what has to be changed.
>>
>> I've enhanced read/write commands (e.g. memory read --as <id> ...) and RSP
>> protocol (new packet) so that the stub can read/write properly. That wasn't
>> that complicated.
>
> It might be nice to add a new RSP protocol packet that asks for the address
> space names/values:
>
> qGetAddressSpaces
>
> which would return something like:
>
> 1:text;2:data1,3:data2
>
> or it would return not supported. If we get a valid return value from
> qGetAddressSpaces, then it enables the use of the new packet you added above.
> Else it defaults to using the old memory read functions.
>
>
>>
>> Now I've hit an issue with expressions (LLVMUserExpression.cpp) and local
>> variables (DWARFExpressions.cpp). There is a lot of memory read/write
>> functions that take just an address argument. Is the only way to go to patch
>> all these calls? Has anybody solved it differently?
>
> My quick take is that any APIs that take just a lldb::addr_t would need to
> take something like:
>
> struct SpaceAddress {
> static constexpr uint32_t kNoSpace = 0;
> lldb::addr_t addr;
> uint32_t space;
> };
>
I'm curious why you are suggesting another kind of address, rather than adding
this functionality to Address? When you actually go to resolve an Address in a
target with a process you should have everything you need to know to give it
the proper space. Then fixing the expression evaluator (and anything else that
needs fixing) would be a matter of consistently using Address rather than
lldb::addr_t. That seems general goodness, since converting to an lldb::addr_t
loses information.
Jim
> We would need a default value for "space" (feel free to rename) that
> indicates the default address space as most of our architectures would not
> need this support. If we added a constructor like:
>
> SpaceAddress(lldb::addr_t a) : addr(a), space(kNoSpace) {}
>
> Then all usages of the APIs that used to take just a "lldb::addr_t" would
> implicitly call this constructor and continue to act as needed. Then we would
> need to allow lldb_private::Address objects to resolve to a SpaceAddress:
>
> SpaceAddress lldb_private::Address::GetSpaceAddress(Target *target) const;
>
> Since each lldb_private::Address has a section and each section knows its
> address space. Then the tricky part is finding all locations in the
> expression parser and converting those to track and use SpaceAddress. We
> would probably need to modify the allocate memory packets in the RSP protocol
> to be able to allocate memory in any address space as well.
>
> I didn't spend much time think about correct names above, so feel free to
> suggest alternate naming.
>
> Best advice:
> - make things "just work" to keep changes to a minimum and allowing
> lldb::addr_t to implicitly convert to a SpaceAddress easily
> - when modifying RSP, make sure to check for existence of new feature before
> enabling it
> - query for address space names so when we dump SpaceAddress we can show
> something that means something to the user. This means we would need to query
> the address space names from the current lldb_private::Process for display.
>
> Submitting might go easier if we break it down into chunks:
> 1 - add SpaceAddress and modify all needed APIs to use it
> 2 - add ProcessGDBRemote changes that enable this support
>
> It will be great to support this as a first class citizen within LLDB. You
> might ask the Hexagon folks if they have done anything in case they already
> support this is some shape or form.
>
> Greg Clayton
>
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