From: Jiri Slaby <jslaby@suse.cz>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Vegard Nossum <vegard.nossum@gmail.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>,
Ming Lei <ming.lei@canonical.com>,
LKML <linux-kernel@vger.kernel.org>,
Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH] firmware: declare __{start,end}_builtin_fw as pointers
Date: Fri, 14 Oct 2016 07:52:53 +0200 [thread overview]
Message-ID: <2d5d3a4d-5b9c-2968-df93-6a8369d06634@suse.cz> (raw)
In-Reply-To: <CA+55aFzGXmDX5hBcUoBKuUtja0XXZcOGVvmnwK5LgLnSO6oqKg@mail.gmail.com>
On 06/26/2016, 07:17 PM, Linus Torvalds wrote:
> On Sun, Jun 26, 2016 at 2:24 AM, Vegard Nossum <vegard.nossum@gmail.com> wrote:
>>
>> This is the best I could come up with: assuming gcc is not allowed to
>> reason about what's inside the asm(), this is the only way I could
>> think of to lose the array information without incurring unnecessary
>> overheads. It should also be relatively safe as there is no way to
>> accidentally use the underlying arrays without explicitly declaring
>> them.
>
> Ugh. I worry about the other places where we do things like this,
> depending on the linker just assigning the addresses and us being able
> to compare them.
>
> If there is a compiler option to disable this optimization, I would
> almost prefer that.. Because we really do have a whole slew of these
> things.
Any update on this? Couple months later and I still hit this.
Quick checking shows, that a lot code depends on comparing two arrays
(undefined behaviour):
ftrace_init
count = __stop_mcount_loc - __start_mcount_loc;
tracer_alloc_buffers
if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt)
FWIW this indeed fixes the get_builtin_firmware case for me:
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -97,9 +97,11 @@ extern struct builtin_fw __end_builtin_fw[];
bool get_builtin_firmware(struct cpio_data *cd, const char *name)
{
#ifdef CONFIG_FW_LOADER
- struct builtin_fw *b_fw;
+ struct builtin_fw *b_fw = __start_builtin_fw;
- for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
+ OPTIMIZER_HIDE_VAR(b_fw);
+
+ for (; b_fw != __end_builtin_fw; b_fw++) {
if (!strcmp(name, b_fw->name)) {
cd->size = b_fw->size;
cd->data = b_fw->data;
What about adding:
#define for_each_vmlinux_symbol(sym, start, stop) \
for (sym = start, OPTIMIZER_HIDE_VAR(sym); sym != stop; sym++)
and converting at least the iterators?
What to do with the array subtractions and comparisons (like tracing), I
don't know (yet).
thanks,
--
js
suse labs
next prev parent reply other threads:[~2016-10-14 5:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-25 15:04 [PATCH] firmware: declare __{start,end}_builtin_fw as pointers Vegard Nossum
2016-06-25 21:06 ` Vegard Nossum
2016-06-26 9:24 ` Vegard Nossum
2016-06-26 17:17 ` Linus Torvalds
2016-10-14 5:52 ` Jiri Slaby [this message]
2016-10-14 6:25 ` Vegard Nossum
2016-10-14 6:30 ` Jiri Slaby
2016-06-28 12:23 George Spelvin
2016-06-28 20:08 ` Linus Torvalds
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