Re: ftrace bug

From: Arend van Spriel
Date: Tue Mar 08 2022 - 05:53:44 EST

On 3/7/2022 2:24 PM, Steven Rostedt wrote:
On Mon, 7 Mar 2022 12:26:45 +0100
Arend van Spriel <arend.vanspriel@xxxxxxxxxxxx> wrote:

Hi Steven,

I wanted to use FTRACE on an ARM platform and I hit the following
warning which results in ftrace bug. This happens upon loading a module.
Looking up the warning I suspect the branch target is too far off. The
module is quite large and therefor not loaded in the modules section. Is
there a way to exclude a module. In ftrace_module_init I see a check for
!mod->num_ftrace_callsites. Is there a way to avoid creating ftrace
callsites in a module?

Are you sure it's the size. Just want to make sure that's the reason before
going with different solutions.

Interpreting the warning statement in insn.c and given the fact that the module is loaded at 0xe3xxxxxx instead of kernel module space at 0xbfxxxxxx I made this assumption, but ....


Regards,
Arend

------------[ cut here ]------------

WARNING: CPU: 2 PID: 1525 at arch/arm/kernel/insn.c:47
__arm_gen_branch+0x70/0x78

CPU: 2 PID: 1525 Comm: insmod Tainted: P 4.19.183 #2

Hardware name: Generic DT based system

[<c02139e4>] (unwind_backtrace) from [<c020d4f8>] (show_stack+0x20/0x24)

[<c020d4f8>] (show_stack) from [<c0922aec>] (dump_stack+0x98/0xac)

[<c0922aec>] (dump_stack) from [<c0919b98>] (__warn.part.0+0xcc/0xe8)

[<c0919b98>] (__warn.part.0) from [<c0919d4c>]
(warn_slowpath_null+0x54/0x74)
[<c0919d4c>] (warn_slowpath_null) from [<c021225c>]
(__arm_gen_branch+0x70/0x78)
[<c021225c>] (__arm_gen_branch) from [<c02120e4>]
(ftrace_make_nop+0x64/0xec)
[<c02120e4>] (ftrace_make_nop) from [<c02ac2b0>]
(ftrace_process_locs+0x370/0x4b4)

[<c02ac2b0>] (ftrace_process_locs) from [<c02af538>]
(ftrace_module_init+0x38/0x3c)

[<c02af538>] (ftrace_module_init) from [<c02a47d8>]
(load_module+0x18d0/0x2570)
[<c02a47d8>] (load_module) from [<c02a56f8>]
(sys_finit_module+0xe0/0xf8)
[<c02a56f8>] (sys_finit_module) from [<c0201000>]
(ret_fast_syscall+0x0/0x58)
Exception stack(0xd9b1bfa8 to 0xd9b1bff0)

bfa0: 01170228 00000000 00000003 01170228 00000000
beb7ceb3
bfc0: 01170228 00000000 beb7cdc4 0000017b 00127010 00000000 00000000
00000000
bfe0: beb7cc38 beb7cc28 0001a0dc 00012890

---[ end trace f48808a851a4544a ]---

------------[ cut here ]------------

WARNING: CPU: 2 PID: 1525 at kernel/trace/ftrace.c:2034
ftrace_bug+0xfc/0x394

Three should be more content after the "cut here" that is very relevant (I
hate that cut here, because I constantly need to tell people to show me
more :-p I need to add a "ftrace bug cut here" line.)


Could you show me the output right after that.

... here is the output I think you were looking for:

ftrace failed to modify
[<a82ca82d>] (suspected corrupt symbol)
actual: 63:17:16:eb
Initializing ftrace call sites
ftrace record flags: 2000000
(0)
expected tramp: c0211b88
ftrace failed to modify
[<6c88ec64>] (suspected corrupt symbol)
actual: 72:ab:08:eb
Initializing ftrace call sites
ftrace record flags: 2000000
(0)
expected tramp: c0211b88
ftrace failed to modify
[<b1ed303a>] (suspected corrupt symbol)
actual: 04:12:04:eb
Initializing ftrace call sites
ftrace record flags: 2000000
(0)
expected tramp: c0211b88
ftrace failed to modify
[<eb2fee66>] (suspected corrupt symbol)
actual: d6:7e:00:eb
Initializing ftrace call sites
ftrace record flags: 2000000
(0)
expected tramp: c0211b88

Regards,
Arend

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