counter intuitive remote target behavior in GDB 7.7
David Taylor <[email protected]>
| Newsgroups | gmane.comp.gdb.devel |
|---|---|
| Message-ID | <3354.1398977622@usendtaylorx2l> |
I'm seeing some counter intuitive remote target behavior in GDB 7.7. We're writing a new GDB stub to replace our old GDB stub and there are some behaviors by GDB that seem counter intuitive when talking to the remote target. I start GDB with an ELF file, I set debug packet (so I can see the behavior I'm describing here), target-async, non-stop, turn off paging (set height 0) and then I do a target remote with appropriate arguments. NOTE: remote, not extended-remote. We might support extended-remote in the future, but not yet. GDB sends a qSupported packet; we respond saying what we support; GDB is happy with the response. GDB sends Hg0 (select any thread), we say OK. GDB sends QNonStop:1, we say OK, GDB sends qfThreadInfo, we respond with a list of 50+ thread ids (the example in front of me has 65 thread ids). qAttached -- we respond '1' (yes, we support qAttached, no you didn't create the process / thread that you are attached to). vCont? -- we respond with vCont;c;C;s;S;t Everything is fine so far; *BUT*, notably, GDB has NOT asked what thread it got when it did the Hg0 -- no qC packet has been seen. GDB now does a vCont;t:1 To which I want to say WTF? It *IS* okay for the user to explicitly and intentionally stop thread 1 or *MOST* threads on the system. If you explicitly stop a thread and you screw yourself, well it's your fault -- be more careful next time. It is *NOT* okay for GDB to 'randomly' decide to stop thread 1 (or any other thread for that matter). When Hg0 was received the stub selected a good thread for GDB to stop (in fact, the thread is likely already stopped). GDB now does qsThreadInfo to get the rest of the thread list. Then a qTStatus (T0;tnotrun:0 for the example in front of me), qTfV (empty -- no thread state variables yet in the new stub). Then '?' and a sequence of vStopped packets to get the list of currently stopped threads. *FINALLY* GDB issues a qC to which, in this instance we respond with QC41 -- thread 65. Then it's qOffsets, qSymbol, another qTStatus, and a qTfP. Next it does a Hg1 (the first stopped thread -- stopped only because GDB decided to stop it!); reads the thread's registers, and reads memory at the current pc location. Then 4 qTStatus messages within nothing in between. Then it goes through each of the remaining stopped threads, reads the registers and the memory at the stopped pc location. To summarize -- It asked the stub to pick a current thread; which the stub did. It eventually asked the stub which thread it picked -- never using the result; but not until after first stopping a thread of its own choosing. It then changed the current thread several times -- throwing away the thread selection that was done initially. And it did a total of 6 qTStatus messages -- 4 of them without any other messages in between. Comments anyone?