8:43 p.m.
Hi Dave,
Here's my answers, I saw your other post and it looks like you are
seeing the same concept as I am anyway.
On 06/13/2014 07:59 AM, Dave Anderson wrote:
----- Original Message -----
> When the crash command line includes two filenames where one is a
> compressed kernel and the other is a debuginfo file and they appear in
> that order then if the uncompressed temporary version of the kernel is
> actually larger than the debuginfo then crash will end with an error but
> will also unlink the debuginfo file and will not clean up the (intended
> temporary) uncompressed copy of the kernel.
Hi Dave,
It's taken me awhile to wrap my head around this, but my first question is:
how is it possible that the uncompressed stripped kernel can possibly be
larger than the debuginfo file?
It took an accidental kernel build outcome where vmlinux.gz was built
with code+text+debuginfo included and a debuginfo was created from it
anyway then the command line had something like:
crash vmlinux.gz vmlinux.debug vmdump
but crash had no authority to unlink vmlinux.debug and fail to unlink
the uncompressed vmlinux temporary regardless of the unexpectedly
unnecessary command-line elements.
I only have old RHEL3 kernels as examples, but the .debug versions
of the kernel are 5 to 6 times larger than the stripped kernel.
That is normal in the cases I see most of the time so the symptoms were
unexpected (and uncommon to be fair).
> This patch at least fixes the unintended unlink and leaving the
> temporary present. It doesn't fix the failure to start but that's
> because the wrong files are assumed the debuginfo and kernel. The size
> case that led to this discovery is probably rare.
Is the unintended unlink() done in the first display_sys_stats() or
in clean_exit()?
clean_exit() at this:
if ((pc->namelist_orig) && file_exists(pc->namelist, NULL))
unlink(pc->namelist);
pc->namelist_orig is vmlinux.gz
pc->namelist is vmlinux.debug
pc->namelist_debug is vmlinux_XXXXXX
where _XXXXXX is replaced with the unique name element. namelist_orig is
associated with what's currently in namelist_debug and the actual unlink
used should have been this:
if ((pc->namelist_debug_orig) && file_exists(pc->namelist_debug, NULL))
unlink(pc->namelist_debug);
pc->namelist_debug_orig is NULL at the point of failure.
And then with your fix applied, why does the crash session still
fail?
Because for the case described crash used the uncompressed vmlinux.gz as
namelist_debug for gdb and vmlinux.debug as namelist. The method of
detection of which file is debug info for gdb is safe most of the time
but you can create a kernel where the vmlinux is larger than the
vmlinux.debug and it causes crash to fail to start because the namelist
that gets used has no code.
--
David.
> The cause is that evidence of a temporary file to unlink is that there
> is a value in pc->namelist and pc->namelist_orig (or pc->namelist_debug
> and pc->namelist_orig_debug) but when the file size test in
> select_namelist() results in the pc->namelist copy to pc->namelist_debug
> the _orig is not copied as well so the implied file to unlink is the one
> set in pc->namelist (the debuginfo filename now).
>
> The patch causes a populated namelist_orig value to be swapped with
> namelist_debug_orig if the namelist value is copied to namelist_debug.
>
> Signed-off-by: David Mair <dmair(a)suse.com>
> ---
> symbols.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/symbols.c b/symbols.c
> index 4c6fbf4..e1ed719 100644
> --- a/symbols.c
> +++ b/symbols.c
> @@ -3520,6 +3520,7 @@ int
> select_namelist(char *new)
> {
> struct stat stat1, stat2;
> + char *namecp;
>
> if (pc->server_namelist) {
> pc->namelist_debug = new;
> @@ -3533,6 +3534,12 @@ select_namelist(char *new)
>
> if (stat1.st_size > stat2.st_size) {
> pc->namelist_debug = pc->namelist;
> + if (pc->namelist_orig)
> + {
> + namecp = pc->namelist_debug_orig;
> + pc->namelist_debug_orig = pc->namelist_orig;
> + pc->namelist_orig = namecp;
> + }
> pc->namelist = new;
> } else if (stat2.st_size > stat1.st_size)
> pc->namelist_debug = new;
>
> --
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--
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