[Crash-utility] [RFC v2] gcore: process core dump feature for crash utility

Hello. This is the RFC version 2 of gcore sub-command that provides a process core dump feature for crash utility. During the period from RFC v1, I had investigated how to restore user-mode register values. The patch reflects the investigation. Any comments or suggestions are welcome. Changes in short ================ The changes include: 1) implement a collection of user-space register values more appropriately, but not ideally. 2) re-design gcore sub-command as an extension module By (1), GDB's bt command displays backtrace normally. diffstat ouput Makefile | 6 +- defs.h | 2 + extensions/gcore.c | 21 + extensions/gcore.mk | 48 + extensions/libgcore/2.6.34/x86_64/gcore.c | 2033 +++++++++++++++++++++++++++++ extensions/libgcore/2.6.34/x86_64/gcore.h | 651 +++++++++ netdump.c | 27 + tools.c | 1 - 8 files changed, 2787 insertions(+), 2 deletions(-) Current Status ============== I've continued to develop gcore sub-command, but this version is still under development. Ultimately, I'm going to implement gcore as I described in RFC v1 and as I will explain in ``Detailed Changes and Issues'' below. How to build and use ==================== I've attached the patchset to this mail. - crash-gcore-RFCv2.patch Please use crash version 5.0.5 on x86_64. Follow the next instructions: $ tar xf crash-5.0.5.tar.gz $ cd crash-5.0.5/ $ patch -p 1 < crash-gcore-v2.patch $ make $ make extensions $ crash <debuginfo> <vmcore> .... (*) crash> extend gcore.so In (*), gcore.so is generated under the extensions/ directory. Detailed Changes and Issues =========================== 1) implement collection of user-space register values more appropriately, but not ideally The previous version doesn't retrieve appropriate register values because it doesn't consider save/restore operations at interrupts on kernel at all. I've added restore operations according to which kinds of interrupts the target task entered kernel-mode. See fill_pr_reg() in gcore.c. But unfortunately, the current version is still not ideal, since it would take some time to do. More precisely, all part of user-mode registers are not always restored. The full part is saved only at exceptions, NMI and some kinds of system calls. At other kinds of interrupts, saved are register values except for 6 callee-saved registers: rbp, rbx, r12, r13, r14, r15. In theory, these can be restored using Call Frame Information generated by a compiler as part of debugging information, whose section name is .debug_frame, which tells us offsets of respective callee-saved registers. But currently, I don't do this yet, since I don't find any useful library to do this. Yes, I think I can implement it manually, but it would take some time. I've of course found unwind_x86_32_64.c providing related library but it looks to me unfinished. On the other hand, a frame pointer, rbp, can be restored by unwinding it repeatedly until its address value reaches any user-space address. 2) re-design gcore sub-command as an extension module In respond to my previous post, Dave gave me a suggestion that gcore subcommand should be provided as an extension module per kernel versions and type of architecutes, since process core dump feature inherently depends on kernel data structures. I agreed the suggestion and have tried to redesign the patchset. Although the current patchset merely moved gcore files into ./extensions directory, I've also considered better design. That is, (1) architecture- or kernel-version independent part is provided just under ./extensions (2) only architecture- or kernel-version specific part is provided as certain extension module. The next directory structure depicts this shortly: crash-5.0.5/ extensions/ gcore.mk gcore.c ... (1) libgcore/ ... (2) 2.6.34/ x86_64/ gcore_note.h gcore_note.c I think it relatively easily feasible by porting regset interface in kernel, which is used to implement ptrace feature, hiding implementation details on many architectures. Also, it helps port kernel codes in gcore and maintain source codes ranging over a variety of kernel versions on multiple architectures uniformly. I'm going to re-implement this way in the next version. From that version, I won't change gcore source code dramatically, change only when adding newly extension modules. Thanks -- HATAYAMA Daisuke