----- Original Message -----
> On Mon, Oct 01, 2018 at 09:37:10AM -0400, Dave Anderson wrote:
> >
> >
> > ----- Original Message -----
> > > Implemented support for 16k stack size that was introduced by commit
> > > 6538b8ea886e472f4431db8ca1d60478f838d14b titled "x86_64: expand kernel
> > > stack to 16K".
> > > Without the patch, kernels has 16k stack, leading to errors in commands
> > > such as "bt" and any command regarding 8K stack.
> > > Add a new "--machdep stacksize=<value>" option that can be used to
> > > override the default machdep->stacksize value which is 8k.
> >
> > The x86_64 default value of 8K is basically a leftover value that each of
> > the architectures originally used for setting machdep->stacksize. But for
> > quite some time now, those values should get overridden later on here
> > in task_init():
> >
> > STRUCT_SIZE_INIT(task_union, "task_union");
> > STRUCT_SIZE_INIT(thread_union, "thread_union");
> >
> > if (VALID_SIZE(task_union) && (SIZE(task_union) != STACKSIZE())) {
> > error(WARNING, "\nnon-standard stack size: %ld\n",
> > len = SIZE(task_union));
> > machdep->stacksize = len;
> > } else if (VALID_SIZE(thread_union) &&
> > ((len = SIZE(thread_union)) != STACKSIZE())) {
> > machdep->stacksize = len;
> > } else if (!VALID_SIZE(thread_union) && !VALID_SIZE(task_union)) {
> > if (kernel_symbol_exists("__start_init_task") &&
> > kernel_symbol_exists("__end_init_task")) {
> > len = symbol_value("__end_init_task");
> > len -= symbol_value("__start_init_task");
> > ASSIGN_SIZE(thread_union) = len;
> > machdep->stacksize = len;
> > }
> > }
> >
> I compiled latest kernel and latest crash and run a qemu guest machine with
> the latest compliled kernel
> image.
> In this case, STRUCT_SIZE_INIT initialized size_table.task_union and
> size_table.thread_union with -1. So machdep->stacksize did NOT get
> overridden.
> > As of Linux 4.18 at least, x86_64 still uses the thread_union declaration.
> > For example:
> >
> > crash> thread_union
> > union thread_union {
> > struct task_struct task;
> > unsigned long stack[2048];
> > }
> > SIZE: 16384
> > crash>
> >
> > On what kernel version are you seeing the obsolete 8k stacksize being used?
> > What does the command above show on your system?
> kernel version is upstream Linux 4.18
> (commit#94710cac0ef4ee177a63b5227664b38c95bbf703)
> (git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git).
>
> "bt" command in crash shows "bt: invalid RSP: ffffc9000069bc08
> bt->stackbase/stacktop: ffffc90000698000/ffffc9000069a000 cpu: 0".
>
> BestRegards
> Sean
Ok, the most recent 4.18 kernel I have on hand is this one:
crash> sys | grep RELEASE
RELEASE: 4.18.0-20.el8.x86_64
crash>
and its debuginfo data contains the "thread_union" information:
crash> thread_union
union thread_union {
struct task_struct task;
unsigned long stack[2048];
}
SIZE: 16384
crash>
but if it did not, then code should then calculate the stack
size from the difference between the "__start_init_task" and
"__end_init_task" symbols:
crash> sym __start_init_task
ffffffffa7800000 (D) __start_init_task
crash> sym __end_init_task
ffffffffa7804000 (D) __end_init_task
crash>
Does your kernel not show/contain those 2 symbols?
Dave
> >
> > Thanks,
> > Dave
> >
> >
> >
> >
> > >
> > > Signed-off-by: Sean Fu <fxinrong@xxxxxxxxx>
> > > ---
> > > x86_64.c | 9 +++++++++
> > > 1 file changed, 9 insertions(+)
> > >
> > > diff --git a/x86_64.c b/x86_64.c
> > > index 7d01140..1798f05 100644
> > > --- a/x86_64.c
> > > +++ b/x86_64.c
> > > @@ -5716,6 +5716,15 @@ parse_cmdline_args(void)
> > > continue;
> > > }
> > > }
> > > + } else if (STRNEQ(arglist[i], "stacksize=")) {
> > > + p = arglist[i] + strlen("stacksize=");
> > > + if (strlen(p)) {
> > > + value = stol(p, RETURN_ON_ERROR|QUIET, &errflag);
> > > + if (!errflag) {
> > > + machdep->stacksize = value;
> > > + continue;
> > > + }
> > > + }
> > > }
> > >
> > > error(WARNING, "ignoring --machdep option: %s\n", arglist[i]);
> > > --
> > > 2.6.2
> > >
> > >
>
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