Hello, On Sun, Mar 20, 2016 at 12:48:30PM +0900, Namhyung Kim wrote: > On Fri, Mar 11, 2016 at 10:21:59AM +0100, Uwe Kleine-König wrote: > > On Wed, Jan 13, 2016 at 09:51:28AM +0100, Marc Kleine-Budde wrote: > > > Hello, > > > > > > I'm on a ARMv5 (freescale mx25) and seeing this ftrace bug during bootup: > > > > > > > [ 0.059235] ------------[ cut here ]------------ > > > > [ 0.059449] WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:1938 > > > > ftrace_bug+0x210/0x2c8() > > > > [ 0.059645] Modules linked in: > > > > [ 0.059780] CPU: 0 PID: 0 Comm: swapper Not tainted > > > > 4.0.9-20151211-1-g45dbe7d2c077 #1 > > > > [ 0.059966] Hardware name: Freescale i.MX25 (Device Tree Support) > > > > [ 0.060157] [<8000f494>] (unwind_backtrace) from [<8000ce3c>] > > > > (show_stack+0x20/0x24) > > > > [ 0.060396] [<8000ce3c>] (show_stack) from [<8041ea68>] > > > > (dump_stack+0x20/0x28) > > > > [ 0.060630] [<8041ea68>] (dump_stack) from [<8001a74c>] > > > > (warn_slowpath_common+0x88/0xc0) > > > > [ 0.060853] [<8001a74c>] (warn_slowpath_common) from [<8001a840>] > > > > (warn_slowpath_null+0x2c/0x34) > > > > [ 0.061091] [<8001a840>] (warn_slowpath_null) from [<80083748>] > > > > (ftrace_bug+0x210/0x2c8) > > > > [ 0.061332] [<80083748>] (ftrace_bug) from [<80083bb8>] > > > > (ftrace_process_locs+0x330/0x6f0) > > > > [ 0.061576] [<80083bb8>] (ftrace_process_locs) from [<805bdc84>] > > > > (ftrace_init+0x8c/0x14c) > > > > [ 0.061815] [<805bdc84>] (ftrace_init) from [<805b0c80>] > > > > (start_kernel+0x33c/0x3b4) > > > > [ 0.062039] [<805b0c80>] (start_kernel) from [<80008040>] > > > > (0x80008040) > > > > [ 0.062238] ---[ end trace cb88537fdc8fa200 ]--- > > > > [ 0.062364] ftrace failed to modify [<8000c7d8>] > > > > walk_stackframe+0x24/0x44 > > > > [ 0.062544] actual: 16:ff:2f:e1 > > > > [ 0.062702] ftrace record flags: 0 > > > > [ 0.062803] (0) expected tramp: 8000e864 > > > > > > The problem is that walk_stackframe ends up in the __mcount_loc section, > > > although it has a "notrace" attribute: > > > > Not having much clue about elf and stuff, but being hit by this problem > > I added some debug output to recordmcount.c and found that > > sift_rel_mcount (aka sift32_rel_mcount) loops over .rel.text which looks > > as follows for me: > > > > $ readelf -R .rel.text arch/arm/kernel/stacktrace.o > > ... > > Relocation section '.rel.text' at offset 0xb5c contains 15 entries: > > Offset Info Type Sym.Value Sym. Name > > 0000001c 00000028 R_ARM_V4BX > > 0000002c 00001d1c R_ARM_CALL 00000000 unwind_frame > > 00000044 00001f1c R_ARM_CALL 00000000 __gnu_mcount_nc > > 00000104 0000201c R_ARM_CALL 00000000 in_sched_functions > > 00000118 00002102 R_ARM_ABS32 00000000 __exception_text_start > > 0000011c 00002202 R_ARM_ABS32 00000000 __exception_text_end > > 00000130 00001f1c R_ARM_CALL 00000000 __gnu_mcount_nc > > 00000194 00001c1c R_ARM_CALL 00000000 walk_stackframe > > 000001e0 00000902 R_ARM_ABS32 0000003c save_trace > > 000001e4 00000c02 R_ARM_ABS32 00000120 __save_stack_trace > > 000001ec 00001f1c R_ARM_CALL 00000000 __gnu_mcount_nc > > 00000218 00001f1c R_ARM_CALL 00000000 __gnu_mcount_nc > > 00000260 00001c1c R_ARM_CALL 00000000 walk_stackframe > > 0000028c 00000902 R_ARM_ABS32 0000003c save_trace > > 00000294 00001f1c R_ARM_CALL 00000000 __gnu_mcount_nc > > ... > > > > and the unwanted entry in __mcount_loc is generated from the first line > > which isn't a call, but just the information that there is a bx call > > that needs a fixup for ARMv4 machines (that don't support the bx > > instruction). > > > > For this entry get_mcountsym returns 0. > > > > recordmcount.pl only operates on R_ARM_(CALL|PC24|THM_CALL) types for > > ARM and so does it right. > > Hmm.. that means we need to check the reloc types? It seems the > binutils treats R_ARM_THM_PC22 as R_ARM_THM_CALL. > > in /usr/include/elf.h: > #define R_ARM_SBREL32 9 > #define R_ARM_THM_PC22 10 /* PC relative 24 bit (Thumb32 BL). */ > #define R_ARM_THM_PC8 11 /* PC relative & 0x3FC > > in binutils-gdb/include/elf/arm.h: > RELOC_NUMBER (R_ARM_SBREL32, 9) > RELOC_NUMBER (R_ARM_THM_CALL, 10) > RELOC_NUMBER (R_ARM_THM_PC8, 11) > > > So following patch (untested) works for you?
Yes, it changes the output of $(readelf -R __mcount_loc arch/arm/kernel/stacktrace.o) from Hex dump of section '__mcount_loc': 0x00000000 24000000 54000000 6c010000 34020000 $...T...l...4... 0x00000010 6c020000 f4020000 l....... to Hex dump of section '__mcount_loc': 0x00000000 54000000 6c010000 34020000 6c020000 T...l...4...l... 0x00000010 f4020000 .... on top of 4.5. I don't have the machine handy where I saw the problem, so I cannot test at the moment, but I assume your change is fine. Thanks Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |
