> On Mar 23, 2021, at 1:36 PM, Greg Clayton <clayb...@gmail.com> wrote:
>
>
>
>> On Mar 22, 2021, at 11:01 PM, Jason Molenda <jmole...@apple.com> wrote:
>>
>> Hi, I'm working with an Apple team that has a gdb RSP server for JTAG
>> debugging, and we're working to add the ability for it to tell lldb about
>> the UUID and possibly address of a no-dynamic-linker standalone binary, or
>> firmware binary. Discovery of these today is ad-hoc and each different
>> processor has a different way of locating the main binary (and possibly
>> sliding it to the correct load address).
>>
>> We have two main ways of asking the remote stub about binary images today:
>> jGetLoadedDynamicLibrariesInfos on Darwin systems with debugserver, and
>> qXfer:libraries-svr4: on Linux.
>>
>> jGetLoadedDynamicLibrariesInfos has two modes: "tell me about all libraries"
>> and "tell me about libraries at these load addresses" (we get notified about
>> libraries being loaded/unloaded as a list of load addresses of the binary
>> images; binaries are loaded in waves on a Darwin system). The returned JSON
>> packet is heavily tailored to include everything lldb needs to know about
>> the binary image so it can match a file it finds on the local disk to the
>> description and not read any memory at debug time -- we get the mach-o
>> header, the UUID, the deployment target OS version, the load address of all
>> the segments. The packets lldb sends to debugserver look like
>> jGetLoadedDynamicLibrariesInfos:{"fetch_all_solibs":true}
>> or
>> jGetLoadedDynamicLibrariesInfos:{"solib_addresses":[4294967296,140733735313408,..]}
>>
>>
>> qXfer:libraries-svr4: returns an XML description of all binary images
>> loaded, tailored towards an ELF view of binaries from a brief skim of
>> ProcessGDBRemote. I chose not to use this because we'd have an entirely
>> different set of values returned in our xml reply for Mach-O binaries and to
>> eliminate extraneous read packets from lldb, plus we needed a way of asking
>> for a subset of all binary images. A rich UI app these days can link to
>> five hundred binary images, so fetching the full list when only a couple of
>> binaries was just loaded would be unfortunate.
>>
>>
>> I'm trying to decide whether to (1) add a new qStandaloneBinaryInfo packet
>> which returns the simple gdb RSP style "uuid:<UUID>;address:0xADDR;"
>> response, or (2) if we add a third mode to jGetLoadedDynamicLibrariesInfos
>> (jGetLoadedDynamicLibrariesInfos:{"standalone_binary_image_info":true}) or
>> (3) have the JTAG stub support a qXfer XML request (I wouldn't want to reuse
>> the libraries-svr4 name and return an XML completely different, but it could
>> have a qXfer:standalone-binary-image-info: or whatever).
>>
>>
>> I figured folks might have opinions on this so I wanted to see if anyone
>> cares before I pick one and get everyone to implement it. For me, I'm
>> inclined towards adding a qStandaloneBinaryInfo packet - the jtag stub
>> already knows how to construct these traditional gdb RSP style responses -
>> but it would be trivially easy for the stub to also assemble a fake XML
>> response as raw text with the two fields.
>
>
> Any reason to not just return any stand alone binary image information along
> with the dynamic libraries from the
> "jGetLoadedDynamicLibrariesInfos:{"fetch_all_solibs":true}" or
> "qXfer:libraries-svr4" packet? If all of the information is the same anyway,
> no need to treat them any differently. We already return the main
> executable's info in those packets and that isn't a shared library.
My preference for an entirely different packet (or different qXfer request) is
that it simplifies the ProcessGDBRemote decision of whether there is a
user-process DynamicLoader in effect, or and it simplifies the parsing of the
returned values because we can't expect the stub to provide everything that
lldb-server/debugserver return in jGetLoadedDynamicLibrariesInfos and
libraries-svr4; it's a lot of stuff. At the beginning of the debug session
when we're sniffing out what type of connection this is, we can try a dedicated
packet for getting the standalone binary information and that tells us what it
is. Or we can send the "tell me about all the libraries" darwin/elf packet and
get back a result which has two possible formats -- the ones from
debugserver/lldb-server with all of the information they include, or the
minimal response that this JTAG stub can supply.
It may just be laziness on my part, which is why I wanted to raise this here --
whether to create a new packet or to have
jGetLoadedDynamicLibrariesInfos/libraries-svr4 return a new style of result and
have the parsing code detect which style it is, and decide the dynamic linker
based on that. I think the implementation of the former approach, adding a
qStandaloneBinaryInfo packet (or whatever), would be easier than reusing one of
the existing packets for really different purpose.
>
> I would vote to stay with the jGetLoadedDynamicLibrariesInfos packet unless
> you are going to return enough info in the "qXfer:libraries-svr4" packet to
> allow another debugger to just work when connecting with it. So if you have
> to add custom mach-o stuff that another debugger wouldn't be able to use
> anyway to the XML from "qXfer:libraries-svr4", then I don't see the point in
> using it.
>
> Greg
>
>
_______________________________________________
lldb-dev mailing list
lldb-dev@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
