Hi again,
On Mon, 17 Apr 2023 at 10:30, Nadav Har'El <[email protected]> wrote:
[...]
>> > 6. Please verify the changes to clock_gettime() and nonsleep() to return
>> > EINVAL when given a null pointer is the same in Linux (i.e., that it
>> > doesn't return EFAULT) in that case. It's a bit sad we need to waste time
>> > on these checks :-(
>>
>> I just tested, and on Linux a program passing NULL to clock_gettime()
>> just segfaults...
>
>
> Interesting. Maybe even though clock_gettime() is in section 2 of the manual,
> it isn't a real system call
> and is a C wrapper - which segfaults? Real system calls are supposed to
> return EFAULT, not segfault.
I verified this happens because clock_gettime() is a vsyscall
implemented through the vDSO. This is the backtrace:
Program received signal SIGSEGV, Segmentation fault.
do_hres (ts=<optimized out>, clk=<optimized out>, vd=<optimized out>)
at
/build/linux-lowlatency-UVnJHF/linux-lowlatency-6.2.0/include/vdso/math64.h:21
Downloading source file
/build/linux-lowlatency-UVnJHF/linux-lowlatency-6.2.0/include/vdso/math64.h
21
/build/linux-lowlatency-UVnJHF/linux-lowlatency-6.2.0/include/vdso/math64.h:
Directory not empty.
(gdb) bt
#0 do_hres (ts=<optimized out>, clk=<optimized out>, vd=<optimized out>)
at
/build/linux-lowlatency-UVnJHF/linux-lowlatency-6.2.0/include/vdso/math64.h:21
#1 __cvdso_clock_gettime_common (ts=0x0, clock=1, vd=<optimized out>)
at
/build/linux-lowlatency-UVnJHF/linux-lowlatency-6.2.0/arch/x86/entry/vdso/../../../../lib/vdso/gettimeofday.c:251
#2 __cvdso_clock_gettime_data (clock=1, ts=0x0, vd=<optimized out>)
at
/build/linux-lowlatency-UVnJHF/linux-lowlatency-6.2.0/arch/x86/entry/vdso/../../../../lib/vdso/gettimeofday.c:258
#3 0x0000000000421f66 in clock_gettime ()
#4 0x0000000000401791 in test (ts=0x0) at gettime_test.c:11
#5 0x0000000000401802 in main () at gettime_test.c:23
And the kernel documentation explains that
"
...if you pass a bad pointer to a vDSO function, you might get SIGSEGV
instead of -EFAULT.
"
So, I guess we can remove the NULL check :)
Luca
--
You received this message because you are subscribed to the Google Groups "OSv
Development" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/osv-dev/CAJfkoWq7HqAv1drjf54vr0buwfavY3mLT%2BUQfFrfLTntNXcg5w%40mail.gmail.com.
