DavidSpickett added inline comments.
================ Comment at: lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp:1357 + + if (error.Fail()) + return error; ---------------- omjavaid wrote: > DavidSpickett wrote: > > omjavaid wrote: > > > DavidSpickett wrote: > > > > DavidSpickett wrote: > > > > > DavidSpickett wrote: > > > > > > omjavaid wrote: > > > > > > > ptrace request is a success if number of tags requested is not > > > > > > > equal to no of tags read? If not then this and following > > > > > > > condition may be redundant. > > > > > > Well ptracewrapper doesn't check the iovec, but I'll check the > > > > > > kernel source to see if it's actually possible for it to fail that > > > > > > way. > > > > > In `linux/arch/arm64/kernel/mte.c` `__access_remote_tags` there is a > > > > > comment: > > > > > ``` > > > > > +/* > > > > > + * Access MTE tags in another process' address space as given in mm. > > > > > Update > > > > > + * the number of tags copied. Return 0 if any tags copied, error > > > > > otherwise. > > > > > + * Inspired by __access_remote_vm(). > > > > > + */ > > > > > ``` > > > > > > > > > > *any tags* being the key words. > > > > > > > > > > So the scenario is: > > > > > * ask to read from addr X in page 0, with length of pagesize+some so > > > > > the range spills into page 1 > > > > > * kernel can access page 0, reads tags until the end of the page > > > > > * tries to access page 1 to read the rest, fails, returns 0 (success) > > > > > since *some* tags were read > > > > > * we see the ptrace call succeeded but with less tags than we expected > > > > > > > > > > I don't see it's worth dealing with this corner case here since lldb > > > > > will look before it leaps. It would have errored much earlier here > > > > > because either page 1 isn't in the tracee's memory regions or it > > > > > wasn't MTE enabled. > > > > > > > > > > > > > > Added a comment in the code too. > > > This means emitting less than requested number of tags is legit. However > > > we have set tags vector size equal to whatever we have requested. We set > > > error string which is actually not being used anywhere and can be removed > > > in favor of a log message to help with debugging if needed. > > > > > > Also we need to resize the vector after ptrace request so we use this > > > size in gdb remote reply. > > I'll log that error in in GDBRemoteCommunicationServerLLGS.cpp. > > > > I'll do what you suggested to support partial read on the server side. Then > > lldb client can error if it doesn't get what it expected. > > (testing partial reads on the lldb side is going to be very difficult > > anyway since we'd need a valid smaps entry to even issue one) > If we are following an approach similar to m/M gdb remote packets for tags > then its ok to read partial data in case a part memory in requested address > range was inaccessible. May be make appropriate adjustment for command output > I dont recall what currently emit out for partial memory reads but should be > something like <tags not available> > > I did some digging and lldb-server does not return partial data when a read fails. ``` for (bytes_read = 0; bytes_read < size; bytes_read += remainder) { Status error = NativeProcessLinux::PtraceWrapper( PTRACE_PEEKDATA, GetID(), (void *)addr, nullptr, 0, &data); if (error.Fail()) return error; remainder = size - bytes_read; <...> dst += k_ptrace_word_size; } return Status(); ``` I was able to test partial writes too. There too we don't attempt to restore if we only wrote a smaller amount, writing less than the total is a failure. However, it is true that I'm not handling the syscall properly. I need to loop like readmemory does. So I'm going to do that. Loop until we've read all tags, or return the error we get. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D95601/new/ https://reviews.llvm.org/D95601 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits