On Tue, Apr 17, 2018 at 10:20:08AM +0530, Bhupesh Sharma wrote: > Hi, > > I was working on improving documentation/structure of the upstream > kexec-tools and I was wondering what is the purpose of the 'kdump' > directory inside the kexec-tools. > > This kdump utility seems to cause confusion with the 'kdump' utility > present inside some distributions (for e.g. '/usr/sbin/kdump' present > inside fedora) due to the same naming convention and so we should > populate/modify the kdump man page to indicate the same, so as to > avoid confusion. > > Presently here are the contents of this directory: > > # ls kdump/ > kdump.8 kdump.c Makefile > > - Out of these the kdump man documentation (kdump.8) is just a > placeholder as suggested by the man page documentation: "kdump - This > is just a placeholder until real man page has been written" > > - Looking at kdump.c : > > 1. I understand that this code is mainly used to read a crashdump from > memory. One can run the same using: > > # kdump <start_addr> > > where start_addr is basically the start address of the core dump > (which can also be represented via the 'elfcorehdr' environment > variable being passed to the crash kernel which represents the > physical address of the start of the ELF header) > > 2. This tool needs READ_ONLY access to /dev/mem (so we need to set > CONFIG_STRICT_DEVMEM configuration option accordingly). > > 3. The code thereafter reads (via mmap) and verifies the ELF header. > Subsequently it reads (via mmap) the program header. > > 4. Then we collect all the notes and write on STDOUT all the headers > and notes found in the crashdump collected from memory. > > So, as per my understanding even in absence of (more powerful) tools > like crash (or gdb), we can still go ahead and read the crashdump from > memory and display all the headers and notes present in the same on > standard serial out interface using this kdump utility. > > This is probably a good to have feature for systems which have very > simple/minimal rootfs (and I see that a few arm32 systems seem to use > the same as well) or are low on memory availability. > > Now, I wanted to confirm if the 'kdump' utility for reading crashdump > collected from memory is still needed (as the last commit is dated > back to 2016 and was done for arm32 systems). If yes, I can go ahead > and enhance the kdump man page to include the description given above > - so that it helps users understand how to run the tool. > > Please share your opinions. Firstly, please use: git://git.armlinux.org.uk/~rmk/kexec-tools.git for ARM systems - this has some important fixes that aren't in the mainline repository. I think the kdump tool is dead. It only supports the 64-bit ELF format, and 32-bit ARM can either be 32-bit ELF or 64-bit ELF format coredumps, depending whether LPAE is enabled. I've asked questions about this, and not got anywhere, so I now recommend not using that tool. Have you checked whether objcopy can copy the coredump from /proc/vmcore to the filesystem? That would permit saving of the coredump image for later inspection by gdb. -- Russell King _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
