linux-kernel - libelf-0.175 breaks objtool

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Date:   Tue, 5 Feb 2019 13:38:21 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: libelf-0.175 breaks objtool

Just a FYI.

After a recent upgrade in debian testing, I was not able to build the
kernel. I have a custom build of gcc, so I thought it was strange that
I was getting something like this (took this from the web, as I don't
have the error anymore with the work around, and currently doing a full
build):

objdump: kernel/.tmp_signal.o: unable to initialize decompress status for section .debug_info                       
objdump: kernel/.tmp_signal.o: unable to initialize decompress status for section .debug_info                       
objdump: kernel/.tmp_signal.o: file format not recognized                                                           
  CC      arch/x86/kernel/platform-quirks.o                                                                         
objdump: arch/x86/kernel/.tmp_ebda.o: unable to initialize decompress status for section .debug_info                
objdump: arch/x86/kernel/.tmp_ebda.o: unable to initialize decompress status for section .debug_info                
objdump: arch/x86/kernel/.tmp_ebda.o: file format not recognized                                                    
objdump: mm/.tmp_swap_slots.o: unable to initialize decompress status for section .debug_info                       
objdump: mm/.tmp_swap_slots.o: unable to initialize decompress status for section .debug_info                       
objdump: mm/.tmp_swap_slots.o: file format not recognized                                   

The web showed this was an error in Arch Linux, with the latest
libelf-0.175. I was confused to why an upgrade broke my build since I
don't even use the distro gcc to build my kernel. But then realized it
was objtool (after doing a make V=1).

To make sure that this was the case, I used the gcc command (leaving it
out here as it was very long) from a make V=1 to get an object file to
play with. Then tried out:

$ objdump -dr arch/x86/events/intel/.tmp_rapl.o

Which dumped the contents of .tmp_rapl.o nicely.

Then performed:

$ ./tools/objtool/objtool orc generate  --module --no-fp --retpoline "arch/x86/events/intel/.tmp_rapl.o";

And then tried again the objdump, but this time I got:

$ objdump -dr arch/x86/events/intel/.tmp_rapl.o
objdump: arch/x86/events/intel/.tmp_rapl.o: unable to initialize decompress status for section .debug_info
objdump: arch/x86/events/intel/.tmp_rapl.o: unable to initialize decompress status for section .debug_info
objdump: arch/x86/events/intel/.tmp_rapl.o: file format not recognized

The work around I did was that I found an older libelf on another box,
copied it to this box and made the symlink point to it. Low and behold,
objtool worked again.

Anyone else stumble across this?

-- Steve