Hi Bhupesh, I'm confused. If the vmlinux cannot be found, then the crash session should bail out after printing the standard error message in find_booted_kernel(): error(INFO, "cannot find booted kernel -- please enter namelist argument\n\n"); If derive_kaslr_offset() is called, then it must have gotten past find_booted_kernel() with a vmlinux file. What am I missing?

----- Original Message ----- > While running crash on KASLR enabled live arm64 kernels I noticed > that the crash would fail after printing the following error messages > if it cannot find vmlinux for the boot'ed system: > > crash: invalid kernel virtual address: 8470 type: "possible" > WARNING: cannot read cpu_possible_map > crash: invalid kernel virtual address: 8270 type: "present" > WARNING: cannot read cpu_present_map > crash: invalid kernel virtual address: 8070 type: "online" > WARNING: cannot read cpu_online_map > crash: invalid kernel virtual address: 8670 type: "active" > WARNING: cannot read cpu_active_map > > crash: cannot resolve "_stext" > > Since vmlinux is not available at the standard expected location, i.e > '/usr/lib/debug/lib/modules/<kernel-version>' directory, so > _stext_vmlinux stays UNINITIALIZED inside 'derive_kaslr_offset()' > and 'relocate' becomes 0. > > Later-on this can lead to 'cannot resolve "_stext"' error in > 'symbol_value()' function. > > We can go ahead and fix the same, but ideally since we are running > on a live system, we should be finding the vmlinux at the standard > location, otherwise we should do proper error handling. > > So this patch errors out earlier, if we don't find a valid value for > '_stext_vmlinux' and prompts the user to refer to the 'usage' > banner. > > Signed-off-by: Bhupesh Sharma <bhsharma(a)redhat.com&gt; > --- > symbols.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/symbols.c b/symbols.c > index 4db9af7bf044..30669950635d 100644 > --- a/symbols.c > +++ b/symbols.c > @@ -663,6 +663,24 @@ derive_kaslr_offset(bfd *abfd, int dynamic, bfd_byte > *start, bfd_byte *end, > return; > } > > + /* For KASLR enabled live kernels, if vmlinux is not available > + * at the standard expected location, i.e > + * '/usr/lib/debug/lib/modules/<kernel-version>' directory, > + * then _stext_vmlinux will be set to NULL or UNINITIALIZED. > + * > + * Later-on this may lead to "_stext" symbol not being resolved > + * properly (which may lead to an ambiguous error message). > + * > + * So, error out earlier here itself, in case _stext_vmlinux > + * is NULL or UNINITIALIZED. > + */ > + if (!st->_stext_vmlinux || (st->_stext_vmlinux == UNINITIALIZED)) { > + error(INFO, "_stext not found in vmlinux :\n" > + " if running a live system -- please provide a suitable vmlinux,\n" > + " otherwise -- please enter namelist argument.\n"); > + program_usage(SHORT_FORM); > + } > + > /* > * To avoid mistaking an mismatched kernel version with > * a kaslr offset, we make sure that the offset is > -- > 2.7.4 > >