----- Original Message ----- > Hi Dave, > > When tring to debug a kernel core file generated from Debian 9.2 + 4.9 kernel > with base address randomized (this core is create for a qemu vm), it gives > the error as: > > WARNING: cannot determine physical base address: defaulting to 0 > > GNU gdb (GDB) 7.6 > Copyright (C) 2013 Free Software Foundation, Inc. > License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> > This is free software: you are free to change and redistribute it. > There is NO WARRANTY, to the extent permitted by law. Type "show copying" > and "show warranty" for details. > This GDB was configured as "x86_64-unknown-linux-gnu"... > > WARNING: failed to init kexec backup region > WARNING: cannot read linux_banner string > > Taking a look at the code around x86_64_virt_phys_base(), it determines > phys_base by searching around machdep->machspec->phys_base(in my case it's > 0) +/-16MB for banner string at banner string offset (get from symbol). > However, with base address randomized, the real physical address could be > far from 0 (or virtual address 0xffffffff80000000). Therefore, -16MB/+16MB > is not enough especially for machine with large ram . I increased it to > 0xFFFFF00000 for my 256g core file and it works. > > - for (phys = (ulong)(-MEGABYTES(16)); phys != MEGABYTES(16+1); > + for (phys = (ulong)(-MEGABYTES(32)); phys != 0xFFFFF00000; > phys += MEGABYTES(1)) { > if (readmem(linux_banner_phys + phys, PHYSADDR, buf, > strlen("Linux version"), "linux_banner search", > QUIET|RETURN_ON_ERROR) && STRNEQ(buf, "Linux version")) { > if (CRASHDEBUG(1)) > fprintf(fp, > "virtual dump phys_base: %lx %s\n", phys, > machdep->machspec->phys_base != phys ? > "override" : ""); > machdep->machspec->phys_base = phys; > return TRUE; > } > } > > Please feel free to let me know if you need sample dumps to verify. Thx. > > Regards, > Ran Hello Ran, The patch is fine, especially given that the x86_64_virt_phys_base() is a last-ditch effort to determine phys_base. Queued for crash-7.2.6: https://github.com/crash-utility/crash/commit/5aa3c1da3e22037aeeca8d745cec1481137c79fe Thanks, Dave -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
