linux-kernel - Re: linux-next: Tree for Apr 14 (objtool crazy)

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Message-ID: <20200414221914.hbvp4dvh47at4nlg@treble>
Date:   Tue, 14 Apr 2020 17:19:14 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: linux-next: Tree for Apr 14 (objtool crazy)

On Tue, Apr 14, 2020 at 06:50:15AM -0700, Randy Dunlap wrote:
> On 4/13/20 7:39 PM, Stephen Rothwell wrote:
> > Hi all,
> > 
> > Changes since 20200413:
> > 
> 
> 
> I killed objtool after 49 minutes of CPU time:
> 
>   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND    
>  6159 rdunlap   30  10   42756   8028      0 R 100.0 0.099  49:19.02 objtool 
> 
> 
> /bin/sh: line 1:  6159 Terminated              ./tools/objtool/objtool orc generate --no-fp --no-unreachable --uaccess drivers/i2c/busses/i2c-parport.o

I took an initial look at this one.  I can dig more tomorrow unless
Peter beats me to it.

(gdb) bt
#0  0x000000000040df55 in sec_offset_hash (sec=0xc30930, offset=4334561216) at elf.h:104
#1  0x000000000040e907 in find_rela_by_dest_range (elf=0x7ffff64a4010, sec=0xc30930, offset=18446744073709551608, len=1) at elf.c:227
#2  0x000000000040ea67 in find_rela_by_dest (elf=0x7ffff64a4010, sec=0xc30710, offset=18446744073709551608) at elf.c:246
#3  0x0000000000408038 in find_jump_table (file=0x427620 <file>, func=0xc32bf0, insn=0xc4f840) at check.c:1118
#4  0x0000000000408242 in mark_func_jump_tables (file=0x427620 <file>, func=0xc32bf0) at check.c:1170
#5  0x00000000004083b6 in add_jump_table_alts (file=0x427620 <file>) at check.c:1215
#6  0x0000000000408b95 in decode_sections (file=0x427620 <file>) at check.c:1413
#7  0x000000000040bf44 in check (_objname=0x7fffffffceff "drivers/i2c/busses/i2c-parport.o", orc=true) at check.c:2508
#8  0x0000000000405580 in cmd_orc (argc=1, argv=0x7fffffffc9d8) at builtin-orc.c:41
#9  0x0000000000411297 in handle_internal_command (argc=6, argv=0x7fffffffc9d0) at objtool.c:96
#10 0x0000000000411349 in main (argc=6, argv=0x7fffffffc9d0) at objtool.c:119

It's an infinite loop in find_rela_by_dest_range() because offset is -8.
That comes from find_jump_table():

  table_offset = text_rela->addend;
  table_sec = text_rela->sym->sec;
  ...
  table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);

which comes from this gem:

00000000000001fd <line_set>:
 1fd:	48 b8 00 00 00 00 00 	movabs $0x0,%rax
 204:	00 00 00 
			1ff: R_X86_64_64	.rodata-0x8

So objtool is getting confused by that -0x8 rela addend.

-- 
Josh