On 2015年07月17日 12:07, Michael Ellerman wrote:
On Fri, 2015-07-17 at 09:27 +0800, Zumeng Chen wrote:
On 2015年07月16日 17:04, Michael Ellerman wrote:
On Thu, 2015-07-16 at 13:57 +0800, Zumeng Chen wrote:
Hi All,
1028ccf5 did a change for sys_call_table from a pointer to an array of
unsigned long, I think it's not proper, here is my reason:
sys_call_table defined as a label in assembler should be pointer array
rather than an array as described in 1028ccf5. If we defined it as an
array, then arch_syscall_addr will return the address of sys_call_table[],
actually the content of sys_call_table[] is demanded by arch_syscall_addr.
so 'perf list' will ignore all syscalls since find_syscall_meta will
return null
in init_ftrace_syscalls because of the wrong arch_syscall_addr.
Did I miss something, or Gcc compiler has done something newer ?
Hi Zumeng,
It works for me with the code as it is in mainline.
I don't quite follow your explanation, so if you're seeing a bug please send
some information about what you're actually seeing. And include the disassembly
of arch_syscall_addr() and your compiler version etc.
Hi Michael,
Hi Zumeng,
Yeah, it seems it was not a good explanation, I'll explain more this time:
1. Whatever we exclaim sys_call_table in C level, actually it is a pointer
to sys_call_table rather than sys_call_table self in assemble level.
No it's not a pointer.
Then what is the second one in the following:
zchen@pek-yocto-build2:$ cat System.map |grep sys_call_table
c000000000009590 T .sys_call_table <-----this is a real sys_call_table.
c0000000014e1b48 D sys_call_table <-----this should be referred by
arch_syscall_addr
The c0000000014e1b48[0] = c000000000009590
A pointer is a location in memory that contains the address of another location
in memory.
Yeah, this definition is right.
arch/powerpc/kernel/systbl.S
47 .globl sys_call_table <--- see here
48 sys_call_table:
Which gives us a .o that looks like:
0000000000000000 <sys_call_table>:
0: R_PPC64_ADDR64 sys_restart_syscall
8: R_PPC64_ADDR64 sys_restart_syscall
10: R_PPC64_ADDR64 sys_exit
18: R_PPC64_ADDR64 sys_exit
ie. at the location in memory called sys_call_table we have *the contents of
the syscall table*.
We do not have *the address* of the syscall table.
You can also see in the System.map:
c000000000bb0798 R sys_call_table
c000000000bb1e58 r cache_type_info
Please refer to `cat System.map` above
ie. sys_call_table occupies 5824 bytes. If it was a pointer it would only
occupy 8 bytes.
Compare to SYS_CALL_TABLE, which *is* a pointer.
c000000001172bf8 d SYS_CALL_TABLE
c000000001172c00 d exception_marker
Note, 8 bytes.
Finally if you look at a running system using xmon:
0:mon> d $sys_call_table
c0000000008f0798 c0000000000a85a0 c0000000000a85a0 |................|
c0000000008f07a8 c000000000099b40 c000000000099b40 |.......@.......@|
This is right sys_call_table. but not what I'm talking about. What I'm
talking about
is that the definition of sys_call_table by that commit will incur the
following result:
sys_call_table[0]= 0xc0000000014e1b48[0] = c000000000009590 <----Only
this one is right the head address of sys_call_table
sys_call_table[1]= 0xc0000000014e1b48[1] = c0000000015b0da8
sys_call_table[2]= 0xc0000000014e1b48[2] = 0
sys_call_table[3]= 0xc0000000014e1b48[3] = c000000000de0984
sys_call_table[4]= 0xc0000000014e1b48[4] = c0000000015b0da8
sys_call_table[5]= 0xc0000000014e1b48[5] = 0
This is definitely not what we want, is that right?
0:mon> la c0000000000a85a0
c0000000000a85a0: .sys_restart_syscall+0x0/0x40
0:mon> la c000000000099b40
c000000000099b40: .SyS_exit+0x0/0x20
0:mon> d $SYS_CALL_TABLE
c000000000ec68f8 c0000000008f0798 7265677368657265 |........regshere|
^
this is the address of sys_call_table
As another example, see hcall_real_table, which is basically identical, and is
also declared as an array in C.
3. What I have seen in 3.14.x kernel,
======================
And so far, no more difference to 4.x kernel from me about this part if
I'm right.
*) With 1028ccf5
perf list|grep -i syscall got me nothing.
*) Without 1028ccf5
root@localhost:~# perf list|grep -i syscall
syscalls:sys_enter_socket [Tracepoint event]
syscalls:sys_exit_socket [Tracepoint event]
syscalls:sys_enter_socketpair [Tracepoint event]
syscalls:sys_exit_socketpair [Tracepoint event]
syscalls:sys_enter_bind [Tracepoint event]
syscalls:sys_exit_bind [Tracepoint event]
syscalls:sys_enter_listen [Tracepoint event]
syscalls:sys_exit_listen [Tracepoint event]
... ...
I don't know why that's happening.
Please just test 4.2-rc2 for now, so that there are not too many variables.
Yeah, maybe right.
Assuming you have CONFIG_FTRACE_SYSCALLS=y, you can see the tracepoints in
Absolutely
Cheers,
Zumeng
debugfs with:
$ ls -la /sys/kernel/debug/tracing/events/syscalls
total 0
drwxr-xr-x 596 root root 0 Jul 17 13:11 .
drwxr-xr-x 45 root root 0 Jul 17 13:11 ..
-rw-r--r-- 1 root root 0 Jul 17 13:33 enable
-rw-r--r-- 1 root root 0 Jul 17 13:11 filter
drwxr-xr-x 2 root root 0 Jul 17 13:11 sys_enter_accept
drwxr-xr-x 2 root root 0 Jul 17 13:11 sys_enter_accept4
drwxr-xr-x 2 root root 0 Jul 17 13:11 sys_enter_access
drwxr-xr-x 2 root root 0 Jul 17 13:11 sys_enter_add_key
...
cheers
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