On Thu, Jun 27, 2019 at 12:08:01AM +0530, 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....@linux.vnet.ibm.com> > --- > scripts/recordmcount.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) Hi,
linuxppc/merge branch latest commit 850f6274c5b5 was failing to boot IBM Power8 Box, and the failure got resolved with this patch. https://github.com/linuxppc/issues/issues/254 # git log -2 --oneline 0e0f55b31ea8 (HEAD -> issue_254) recordmcount: Fix spurious mcount entries on powerpc 850f6274c5b5 (origin/merge, merge) Automatic merge of branches 'master', 'next' and 'fixes' into merge # uname -r 5.2.0-rc6-00123-g0e0f55b31ea8 Tested-by: Satheesh Rajendran <sathn...@linux.vnet.ibm.com> Regards, -Satheesh > > diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h > index 13c5e6c8829c..47fca2c69a73 100644 > --- a/scripts/recordmcount.h > +++ b/scripts/recordmcount.h > @@ -325,7 +325,8 @@ static uint_t *sift_rel_mcount(uint_t *mlocp, > if (!mcountsym) > mcountsym = get_mcountsym(sym0, relp, str0); > > - if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp)) { > + if (mcountsym && mcountsym == Elf_r_sym(relp) && > + !is_fake_mcount(relp)) { > uint_t const addend = > _w(_w(relp->r_offset) - recval + mcount_adjust); > mrelp->r_offset = _w(offbase > -- > 2.22.0 >