On 03/14/2018 02:43 AM, Nicolas Pitre wrote:
> Now, what's the date of include/generated/autoksyms.h compared to
> arch/x86/lib/usercopy_64.o?
>
> If include/generated/autoksyms.h is older than
> arch/x86/lib/usercopy_64.o then the presence of __KSYM_clear_user in the
> former should have instanciated the corresponding EXPORT_SYMBOL() in the
> later.
>
> If it is the other way around then you should compare the time for
> arch/x86/lib/usercopy_64.o against include/config/ksym///clear/user.h.
> If the later is newer than the former then something failed to notice
> that usercopy_64.o wasn't up to date, in which case the makefile or make
> itself might need some investigation.
>
> If not then we'd have to look in the full build log to figure out if
> __KSYM_clear_user existed in the previous version of
> include/generated/autoksyms.h before it was refreshed by
> adjust_autoksyms.sh. If it was then we're back to if #1 above. If not
> then the timestamp for include/config/ksym///clear/user.h hasn't been
> updated as it should.
Here are the timestamps for the fail case:
-rw-r--r-- 1 cocobo cocobo 66424 2018-03-13 17:20:18.000000000 +0100 linux-fail/include/generated/autoksyms.h
-rw-r--r-- 1 cocobo cocobo 121064 2018-03-13 17:16:53.000000000 +0100 linux-fail/arch/x86/lib/usercopy_64.o
-rw-r--r-- 1 cocobo cocobo 0 2018-03-13 17:16:53.000000000 +0100 linux-fail/include/config/ksym///clear/user.h
It's suspicious that usercopy_64.o and ksym///clear/user.h got the same timestamp.
My gut feeling says that ksym///clear/user.h was touched after usercopy_64.o was
built but less than 1 sec had passed so they got the same timestamps due to the
poor timestamp resolution on my old ext4 filesystem. Since the timestamps on
ksym///clear/user.h wasn't newer than usercopy_64.o the rebuild was skipped.
AS arch/x86/lib/putuser.o
AS arch/x86/lib/retpoline.o <---
AS arch/x86/lib/rwsem.o
CC arch/x86/lib/usercopy.o
CC arch/x86/lib/usercopy_64.o <---
AR arch/x86/lib/lib.a
EXPORTS arch/x86/lib/lib-ksyms.o
AR arch/x86/lib/built-in.o
CC virt/lib/irqbypass.o
AR virt/lib/built-in.o
AR virt/built-in.o
CHK include/generated/autoksyms.h
KSYMS symbols: before=0, after=1871, changed=1871
The problematic usercopy_64.o and retpoline.o are built just before ksym. The build
and ksym generation probably happens in less than 1 sec.
Here are the timestamps for the success case:
-rw-r--r-- 1 cocobo cocobo 66424 2018-03-13 16:58:02.000000000 +0100 linux-success/include/generated/autoksyms.h
-rw-r--r-- 1 cocobo cocobo 126912 2018-03-13 16:58:01.000000000 +0100 linux-success/arch/x86/lib/usercopy_64.o
-rw-r--r-- 1 cocobo cocobo 0 2018-03-13 16:54:38.000000000 +0100 linux-success/include/config/ksym///clear/user.h
usercopy_64.o was rebuilt here so it has a more recent timestamp than ksym///clear/user.h.
To test this a bit more I copied the 4.14.23 source to tmpfs and ran the build there.
Tmpfs supports nanosecond timestamps. The build succeeded 16 times in a row. Usually
there is around 50/50 chance of success/failure on ext4.
>>> Also... is the build always failing because of symbols starting with one
>>> or more underscores?
>>
>> The type of failures I've seen so far are:
>>
>> ERROR: "clear_user" [drivers/media/v4l2-core/videodev.ko] undefined!
>> ERROR: "__clear_user" [arch/x86/kvm/kvm.ko] undefined!
>>
>> ERROR: "__fill_rsb" [arch/x86/kvm/kvm-intel.ko] undefined!
>>
>> ERROR: "__put_user_2" [net/ipv4/netfilter/ip_tables.ko] undefined!
>> ERROR: "__put_user_2" [net/ipv4/netfilter/arp_tables.ko] undefined!
>> ERROR: "__put_user_8" [fs/udf/udf.ko] undefined!
>> ERROR: "__put_user_4" [fs/udf/udf.ko] undefined!
>> ERROR: "__put_user_8" [fs/fat/fat.ko] undefined!
>> ERROR: "__put_user_1" [fs/fat/fat.ko] undefined!
>> ERROR: "__put_user_4" [fs/fat/fat.ko] undefined!
>> ERROR: "__put_user_2" [fs/fat/fat.ko] undefined!
>> ERROR: "__put_user_4" [drivers/net/tap.ko] undefined!
>> ERROR: "__put_user_2" [drivers/net/tap.ko] undefined!
>> ERROR: "__put_user_8" [drivers/media/v4l2-core/videodev.ko] undefined!
>> ERROR: "__put_user_1" [drivers/media/v4l2-core/videodev.ko] undefined!
>> ERROR: "__put_user_4" [drivers/media/v4l2-core/videodev.ko] undefined!
>> ERROR: "__put_user_8" [drivers/input/joydev.ko] undefined!
>> ERROR: "__put_user_1" [drivers/input/joydev.ko] undefined!
>> ERROR: "__put_user_4" [drivers/input/joydev.ko] undefined!
>> ERROR: "__fill_rsb" [arch/x86/kvm/kvm-intel.ko] undefined!
>>
>> There might have been others but I didn't save every error message.
>
> Maybe it is just a coincidence, but there is a lot of underscore
> prefixed symbols in that list, except for one case. This translates to
> successive / in the path for the timestamp file. And that one case that
> doesn't fit the pattern does actually aliases a path that does. I wonder
> if the filesystem cache could get confused by successive / in paths
> here, given the non deterministic nature of the build failure you get.
>
> Could you please test with the following patch to validate this
> hypothesis:
>
> diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh
> index 513da1a4a2..2205114add 100755
> --- a/scripts/adjust_autoksyms.sh
> +++ b/scripts/adjust_autoksyms.sh
> @@ -79,6 +79,7 @@ changed=$(
> count=0
> sort "$cur_ksyms_file" "$new_ksyms_file" | uniq -u |
> sed -n 's/^#define __KSYM_\(.*\) 1/\1/p' | tr "A-Z_" "a-z/" |
> +sed -e 's|//*|/|g' -e 's|^/||' |
> while read sympath; do
> if [ -z "$sympath" ]; then continue; fi
> depfile="include/config/ksym/${sympath}.h"
> diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
> index 449b68c4c9..57ae789f91 100644
> --- a/scripts/basic/fixdep.c
> +++ b/scripts/basic/fixdep.c
> @@ -115,7 +115,7 @@ static void usage(void)
> */
> static void print_config(const char *m, int slen)
> {
> - int c, i;
> + int c, prev_c = '/', i;
>
> printf(" $(wildcard include/config/");
> for (i = 0; i < slen; i++) {
> @@ -124,7 +124,9 @@ static void print_config(const char *m, int slen)
> c = '/';
> else
> c = tolower(c);
> - putchar(c);
> + if (c != '/' || prev_c != '/')
> + putchar(c);
> + prev_c = c;
> }
> printf(".h) \\\n");
> }
>
> That would be very interesting if this patch fixed your build failures.
The patch applied with some fuzz to 4.14.23. Using the patch the first two
builds I did succeeded and the third failed like:
Kernel: arch/x86/boot/bzImage is ready (#2)
Building modules, stage 2.
MODPOST 146 modules
ERROR: "__put_user_2" [net/ipv4/netfilter/ip_tables.ko] undefined!
ERROR: "__put_user_2" [net/ipv4/netfilter/arp_tables.ko] undefined!
ERROR: "__put_user_8" [fs/udf/udf.ko] undefined!
ERROR: "__put_user_4" [fs/udf/udf.ko] undefined!
ERROR: "__put_user_8" [fs/fat/fat.ko] undefined!
ERROR: "__put_user_1" [fs/fat/fat.ko] undefined!
ERROR: "__put_user_4" [fs/fat/fat.ko] undefined!
ERROR: "__put_user_2" [fs/fat/fat.ko] undefined!
ERROR: "__put_user_4" [drivers/net/tap.ko] undefined!
ERROR: "__put_user_2" [drivers/net/tap.ko] undefined!
ERROR: "__put_user_8" [drivers/media/v4l2-core/videodev.ko] undefined!
ERROR: "__put_user_1" [drivers/media/v4l2-core/videodev.ko] undefined!
ERROR: "__put_user_4" [drivers/media/v4l2-core/videodev.ko] undefined!
ERROR: "__put_user_8" [drivers/input/joydev.ko] undefined!
ERROR: "__put_user_1" [drivers/input/joydev.ko] undefined!
ERROR: "__put_user_4" [drivers/input/joydev.ko] undefined!
ERROR: "__fill_rsb" [arch/x86/kvm/kvm-intel.ko] undefined!
make[1]: *** [scripts/Makefile.modpost:92: __modpost] Error 1
make: *** [Makefile:1218: modules] Error 2
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