On 01/13/2016 09:51 AM, 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: > >> $ grep notrace arch/arm/kernel/stacktrace.c | grep walk_stackframe >> void notrace walk_stackframe(struct stackframe *frame, > > > To reproduce: > > - use the arm compiler from kernel.org: >> https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.9.0/x86_64-gcc-4.9.0-nolibc_arm-unknown-linux-gnueabi.tar.xz > > - linus master > (67990608c8b9 Merge tag 'pm+acpi-4.5-rc1-1' of > git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm) > > - a ARMv5 config >> make imx_v4_v5_defconfig > > - switch on the function tracer and dynamic ftrace >> CONFIG_HAVE_FUNCTION_TRACER=y >> CONFIG_HAVE_FUNCTION_GRAPH_TRACER=y >> CONFIG_HAVE_DYNAMIC_FTRACE=y > > - build the object file that contains walk_stackframe: >> $ make arch/arm/kernel/stacktrace.o > > > Observations: > > - There is no branch to the mcount function ("bl 0 <__gnu_mcount_nc>"), > which is good: >> $ objdump -d arch/arm/kernel/stacktrace.o |grep "<walk_stackframe>:" -A12 >> 00000000 <walk_stackframe>: >> 0: e1a0c00d mov ip, sp >> 4: e92dd878 push {r3, r4, r5, r6, fp, ip, lr, pc} >> 8: e24cb004 sub fp, ip, #4 >> c: e1a04000 mov r4, r0 >> 10: e1a06001 mov r6, r1 >> 14: e1a05002 mov r5, r2 >> 18: e1a00004 mov r0, r4 >> 1c: e1a01005 mov r1, r5 >> 20: e1a0e00f mov lr, pc >> 24: e12fff16 bx r6 >> 28: e3500000 cmp r0, #0 >> 2c: 189da878 ldmne sp, {r3, r4, r5, r6, fp, sp, pc} > > There are 5 calls to __gnu_mcount_nc in the object file: >> $ objdump -x arch/arm/kernel/stacktrace.o | grep R_ARM_CALL | grep >> __gnu_mcount_nc >> 00000054 R_ARM_CALL __gnu_mcount_nc >> 0000016c R_ARM_CALL __gnu_mcount_nc >> 00000234 R_ARM_CALL __gnu_mcount_nc >> 0000026c R_ARM_CALL __gnu_mcount_nc >> 000002f4 R_ARM_CALL __gnu_mcount_nc > > However there are 6 references in the __mcount_loc section: >> $ readelf -R __mcount_loc arch/arm/kernel/stacktrace.o >> >> >> Hex dump of section '__mcount_loc': >> 0x00000000 24000000 54000000 6c010000 34020000 $...T...l...4... >> 0x00000010 6c020000 f4020000 l....... > > Note: The first and wrong offset is 0x24, which is a "bx r6" (see above > objdump of stacktrace.o): >> 24: e12fff16 bx r6 > > I hacked scripts/Makefile.build to use the perl version of recordmcount, > that works without problems.
Has anyone looked at this issue? regards, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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