Re: [Crash-utility] [PATCH] crash/symbols: Error out earlier in case _stext_vmlinux is NULL or UNINITIALIZED

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