> On Apr 19, 2018, at 10:35 AM, Jim Ingham <jing...@apple.com> wrote:
>
>
>
>> On Apr 19, 2018, at 9:44 AM, Greg Clayton via lldb-dev
>> <lldb-dev@lists.llvm.org> wrote:
>>
>>
>>
>>> On Apr 19, 2018, at 6:51 AM, Zdenek Prikryl via lldb-dev
>>> <lldb-dev@lists.llvm.org> 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.
If we accept lldb_private::Address in all APIs that take a lldb::addr_t
currently, then we need to always be able to get to the target in case we need
to add code to resolve the address everywhere. I am thinking of SpaceAddress as
an augmented lldb::addr_t instead of a section + offset style address. Also,
there will be addresses in the code and data that do not exist in actual
sections. Not saying that you couldn't use lldb_private::Address. I am open to
suggestions though. So your though it remove all API that take lldb::addr_t and
use lldb_private::Address everywhere all the time?
>
> 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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