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SubjectRe: [PATCH] recordmcount: Fix spurious mcount entries on powerpc
Date
On Wed, 2019-06-26 at 18:38:01 UTC, "Naveen N. Rao" wrote:
> The recent change enabling HAVE_C_RECORDMCOUNT on powerpc started
> showing the following issue:
>
> # modprobe kprobe_example
> ftrace-powerpc: Not expected bl: opcode is 3c4c0001
> WARNING: CPU: 0 PID: 227 at kernel/trace/ftrace.c:2001 ftrace_bug+0x90/0x318
> Modules linked in:
> CPU: 0 PID: 227 Comm: modprobe Not tainted 5.2.0-rc6-00678-g1c329100b942 #2
> NIP: c000000000264318 LR: c00000000025d694 CTR: c000000000f5cd30
> REGS: c000000001f2b7b0 TRAP: 0700 Not tainted (5.2.0-rc6-00678-g1c329100b942)
> MSR: 900000010282b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]> CR: 28228222 XER: 00000000
> CFAR: c0000000002642fc IRQMASK: 0
> <snip>
> NIP [c000000000264318] ftrace_bug+0x90/0x318
> LR [c00000000025d694] ftrace_process_locs+0x4f4/0x5e0
> Call Trace:
> [c000000001f2ba40] [0000000000000004] 0x4 (unreliable)
> [c000000001f2bad0] [c00000000025d694] ftrace_process_locs+0x4f4/0x5e0
> [c000000001f2bb90] [c00000000020ff10] load_module+0x25b0/0x30c0
> [c000000001f2bd00] [c000000000210cb0] sys_finit_module+0xc0/0x130
> [c000000001f2be20] [c00000000000bda4] system_call+0x5c/0x70
> Instruction dump:
> 419e0018 2f83ffff 419e00bc 2f83ffea 409e00cc 4800001c 0fe00000 3c62ff96
> 39000001 39400000 386386d0 480000c4 <0fe00000> 3ce20003 39000001 3c62ff96
> ---[ end trace 4c438d5cebf78381 ]---
> ftrace failed to modify
> [<c0080000012a0008>] 0xc0080000012a0008
> actual: 01:00:4c:3c
> Initializing ftrace call sites
> ftrace record flags: 2000000
> (0)
> expected tramp: c00000000006af4c
>
> Looking at the relocation records in __mcount_loc showed a few spurious
> entries:
> RELOCATION RECORDS FOR [__mcount_loc]:
> OFFSET TYPE VALUE
> 0000000000000000 R_PPC64_ADDR64 .text.unlikely+0x0000000000000008
> 0000000000000008 R_PPC64_ADDR64 .text.unlikely+0x0000000000000014
> 0000000000000010 R_PPC64_ADDR64 .text.unlikely+0x0000000000000060
> 0000000000000018 R_PPC64_ADDR64 .text.unlikely+0x00000000000000b4
> 0000000000000020 R_PPC64_ADDR64 .init.text+0x0000000000000008
> 0000000000000028 R_PPC64_ADDR64 .init.text+0x0000000000000014
>
> The first entry in each section is incorrect. Looking at the relocation
> records, the spurious entries correspond to the R_PPC64_ENTRY records:
> RELOCATION RECORDS FOR [.text.unlikely]:
> OFFSET TYPE VALUE
> 0000000000000000 R_PPC64_REL64 .TOC.-0x0000000000000008
> 0000000000000008 R_PPC64_ENTRY *ABS*
> 0000000000000014 R_PPC64_REL24 _mcount
> <snip>
>
> The problem is that we are not validating the return value from
> get_mcountsym() in sift_rel_mcount(). With this entry, mcountsym is 0,
> but Elf_r_sym(relp) also ends up being 0. Fix this by ensuring mcountsym
> is valid before processing the entry.
>
> Fixes: c7d64b560ce80 ("powerpc/ftrace: Enable C Version of recordmcount")
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> Tested-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/80e5302e4bc85a6b685b7668c36c6487b5f90e9a

cheers

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