[lkml]   [2018]   [Nov]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] btrfs: avoid link error with CONFIG_NO_AUTO_INLINE
On 11/4/18, Qu Wenruo <> wrote:
> On 2018/11/3 下午11:39, Arnd Bergmann wrote:
>> On 32-bit ARM with gcc-8, I see a link error with the addition of the
>> fs/btrfs/super.o: In function `btrfs_statfs':
>> super.c:(.text+0x67b8): undefined reference to `__aeabi_uldivmod'
>> super.c:(.text+0x67fc): undefined reference to `__aeabi_uldivmod'
>> super.c:(.text+0x6858): undefined reference to `__aeabi_uldivmod'
>> super.c:(.text+0x6920): undefined reference to `__aeabi_uldivmod'
>> super.c:(.text+0x693c): undefined reference to `__aeabi_uldivmod'
>> fs/btrfs/super.o:super.c:(.text+0x6958): more undefined references to
>> `__aeabi_uldivmod' follow
>> So far this is the only file that shows the behavior, so I'd propose
>> to just work around it by marking the functions as 'static inline'
>> that normally get inlined here.
> As a workaround it looks OK, but it's definitely not the root cause.
>> The reference to __aeabi_uldivmod comes from a div_u64() which has an
>> optimization for a constant division that uses a straight '/' operator
>> when the result should be known to the compiler. My interpretation is
>> that as we turn off inlining, gcc still expects the result to be constant
>> but fails to use that constant value.
> It looks more like a bug in div_u64() optimization.
> Despite this file in btrfs, did you hit the same problem for any other
> file?

Not this time. I've done a creduce on the file and got to this code

struct kstatfs {
u64 f_bfree;
btrfs_calc_avail_data_space(p1) {}
btrfs_statfs(struct kstatfs *p1) {
u64 d = 0;
unsigned e = 1;
for (; a;)
e = btrfs_bg_type_to_factor();
p1->f_bfree = div_u64(0, e) >> c;
div_u64(d, e);
b = btrfs_calc_avail_data_space(&d);

Looking at the assembler code produced by this, it seems to be
the same thing that we dealt with in

>> Cc: Changbin Du <>
>> Fixes: 943b8435c3bd ("kernel hacking: add a config option to disable
>> compiler auto-inlining")
> I can't find it in the mainline kernel, is the commit hash correct?
> If not merged, we should still has a chance to further polish that patch.

It's in linux-next.


 \ /
  Last update: 2018-11-04 23:33    [W:0.145 / U:0.192 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site