Thanks for the feedback, Enrico, I’m relying on the fact that when the wstring is larger than the default size (1GB in your example), we won’t get a ptrace error like EIO or EFAULT. So, there will be no search for a null terminator.
If we can’t rely on the null terminator, it’s hard to know if a different error occurred. The trouble is that there is inconsistency in the PTRACE_PEEK implementation on Linux that is more or less arbitrary (sigh), so the out-of-bounds read can generate EIO or EFAULT. In particular, EIO can mean a number of things: “request is invalid, or an attempt was made to read from or write to an invalid area in the parent's or child's memory, or there was a word-alignment violation, or an invalid signal was specified during a restart request.” – http://linux.die.net/man/2/ptrace In addition, the Linux ProcessMonitor reads in 8-byte chunks, so ReadUTFBufferAndDumpToStream will probably fail (for the right reasons) in the case where at least part of the null terminator was in that block. I see that as an implementation detail that can be resolved in ProcessMonitor by reading smaller chunks until PTRACE_PEEK succeeds (i.e. a good follow-up patch). Do let me know if you feel this is okay to commit as is. Cheers, - Ashok From: Enrico Granata [mailto:[email protected]] Sent: Wednesday, March 27, 2013 6:18 PM To: Thirumurthi, Ashok Cc: [email protected] Subject: Re: [lldb-dev] PATCH for REVIEW - Fix [Bug 15038] LLDB does not support printing wide-character variables on Linux Hi Ashok, thanks for submitting an LLDB patch :) I have looked at the code and while I see where the patch is coming from, I see a potential issue with it. The code in ReadUTFBufferAndDumpToStream, which is what you are editing, is meant to work on a partial string (i.e. one that does not have a NULL terminator at the end). The reason for that is that you might have a wstring that is 1GB long and we would not want to try and read all of it and then display it. What we do is pick a size and only extract that much data. For obvious reasons, your string might be longer than our upper boundary, so you would get a chunk of valid bytes and then no end-of-buffer marker. It looks like your code would fail in that case and produce no summary for a string if an EIO was received before \0. Is there any reason why you can’t just check if (error == EIO and data_read > 0) and if so treat this as a “partial string” condition and keep going? Would that break/crash anything? Best, Enrico Granata ✉ egranata@.com<mailto:egranata@.com> ✆ 27683 On Mar 27, 2013, at 2:52 PM, "Thirumurthi, Ashok" <[email protected]<mailto:[email protected]>> wrote: The root cause for Bug 15038 is a ptrace EIO that can occur because we don't know the size of a (UTF) string and so read a fixed number of characters for strings. The attached fix accepts EIO in the case where data has been read and a null terminator of the correct size and alignment was found. - Ashok -----Original Message----- From: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf [email protected]<mailto:[email protected]> Sent: Tuesday, January 22, 2013 10:13 AM To: [email protected]<mailto:[email protected]> Subject: [lldb-dev] [Bug 15038] New: LLDB does not support printing wide-character variables on Linux http://llvm.org/bugs/show_bug.cgi?id=15038 Bug #: 15038 Summary: LLDB does not support printing wide-character variables on Linux Product: lldb Version: unspecified Platform: PC OS/Version: Linux Status: NEW Severity: enhancement Priority: P Component: All Bugs AssignedTo: [email protected]<mailto:[email protected]> ReportedBy: [email protected]<mailto:[email protected]> Classification: Unclassified Printing a variable of wchar_t type does not behave as expected and results in garbage being printed on the screen. To reproduce, remove the @expectedFailureLinux decorator from TestChar1632T.py and TestCxxWCharT.py and run: python dotest.py --executable <path-to-lldb> lang/cpp/char1632_t lang/cpp/wchar_t -- Configure bugmail: http://llvm.org/bugs/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug. _______________________________________________ lldb-dev mailing list [email protected]<mailto:[email protected]> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev <read-strings.diff>_______________________________________________ lldb-dev mailing list [email protected]<mailto:[email protected]> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
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