Re: [Crash-utility] [PATCH] cmdline: Add a new "--machdep stacksize=<value>".

----- 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(a)gmail.com&gt; > > > --- > > > 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 > > > > > > >