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Scenario 1, ARMv7
=================
If code in arch/arm/kernel/ftrace.c would operate on mcount() pointer
the following may be generated:
00000230 <prealloc_fixed_plts>:
230: b5f8 push {r3, r4, r5, r6, r7, lr}
232: b500 push {lr}
234: f7ff fffe bl 0 <__gnu_mcount_nc>
234: R_ARM_THM_CALL __gnu_mcount_nc
238: f240 0600 movw r6, #0
238: R_ARM_THM_MOVW_ABS_NC __gnu_mcount_nc
23c: f8d0 1180 ldr.w r1, [r0, #384] ; 0x180
FTRACE currently is not able to deal with it:
WARNING: CPU: 0 PID: 0 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1ad/0x230()
...
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.116-... #1
...
[<c0314e3d>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c051a7f1>] (dump_stack+0x81/0xa8)
[<c051a7f1>] (dump_stack) from [<c0321c5d>] (warn_slowpath_common+0x69/0x90)
[<c0321c5d>] (warn_slowpath_common) from [<c0321cf3>] (warn_slowpath_null+0x17/0x1c)
[<c0321cf3>] (warn_slowpath_null) from [<c038ee9d>] (ftrace_bug+0x1ad/0x230)
[<c038ee9d>] (ftrace_bug) from [<c038f1f9>] (ftrace_process_locs+0x27d/0x444)
[<c038f1f9>] (ftrace_process_locs) from [<c08915bd>] (ftrace_init+0x91/0xe8)
[<c08915bd>] (ftrace_init) from [<c0885a67>] (start_kernel+0x34b/0x358)
[<c0885a67>] (start_kernel) from [<00308095>] (0x308095)
---[ end trace cb88537fdc8fa200 ]---
ftrace failed to modify [<c031266c>] prealloc_fixed_plts+0x8/0x60
actual: 44:f2:e1:36
ftrace record flags: 0
(0) expected tramp: c03143e9
Scenario 2, ARMv4T
==================
ftrace: allocating 14435 entries in 43 pages
------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:2029 ftrace_bug+0x204/0x310
CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.5 #1
Hardware name: Cirrus Logic EDB9302 Evaluation Board
[<c0010a24>] (unwind_backtrace) from [<c000ecb0>] (show_stack+0x20/0x2c)
[<c000ecb0>] (show_stack) from [<c03c72e8>] (dump_stack+0x20/0x30)
[<c03c72e8>] (dump_stack) from [<c0021c18>] (__warn+0xdc/0x104)
[<c0021c18>] (__warn) from [<c0021d7c>] (warn_slowpath_null+0x4c/0x5c)
[<c0021d7c>] (warn_slowpath_null) from [<c0095360>] (ftrace_bug+0x204/0x310)
[<c0095360>] (ftrace_bug) from [<c04dabac>] (ftrace_init+0x3b4/0x4d4)
[<c04dabac>] (ftrace_init) from [<c04cef4c>] (start_kernel+0x20c/0x410)
[<c04cef4c>] (start_kernel) from [<00000000>] ( (null))
---[ end trace 0506a2f5dae6b341 ]---
ftrace failed to modify
[<c000c350>] perf_trace_sys_exit+0x5c/0xe8
actual: 1e:ff:2f:e1
Initializing ftrace call sites
ftrace record flags: 0
(0)
expected tramp: c000fb24
The analysis for this problem has been already performed previously,
refer to the link below.
Fix the above problems by allowing only selected reloc types in
__mcount_loc. The list itself comes from the legacy recordmcount.pl
script.
Link: https://lore.kernel.org/lkml/56961010.6000806@pengutronix.de/
Cc: stable@vger.kernel.org
Fixes: ed60453fa8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
927d780ee3