two more objtool warnings: lib/ubsan.o and fs/fs_pin.o

two more objtool warnings: lib/ubsan.o and fs/fs_pin.o

[Arnd Bergmann]

Hi Josh,

I ran into two more warnings with the two patches you sent me in private,
using gcc-7.1.1:

lib/ubsan.o: warning: objtool: val_to_string.constprop.7()+0x97: leave
instruction with modified stack frame
.config: https://pastebin.com/dl/g04Dwdwx

fs/fs_pin.o: warning: objtool: pin_kill()+0x139: stack state mismatch:
cfa1=7+88 cfa2=7+96
.config: https://pastebin.com/dl/6gK6MadB

I assume you are faster at analysing than me, so I have not tried to get
to the bottom of these at all. Let me know if you need help reproducing
the warnings. It's also possible that they are fixed by some other patches
that you already sent but that are not in linux-next yet.

       Arnd

Re: two more objtool warnings: lib/ubsan.o and fs/fs_pin.o

[Josh Poimboeuf]

On Fri, Jul 28, 2017 at 01:25:27PM +0200, Arnd Bergmann wrote:
> Hi Josh,
> 
> I ran into two more warnings with the two patches you sent me in private,
> using gcc-7.1.1:
> 
> lib/ubsan.o: warning: objtool: val_to_string.constprop.7()+0x97: leave
> instruction with modified stack frame
> .config: https://pastebin.com/dl/g04Dwdwx
> 
> fs/fs_pin.o: warning: objtool: pin_kill()+0x139: stack state mismatch:
> cfa1=7+88 cfa2=7+96
> .config: https://pastebin.com/dl/6gK6MadB
> 
> I assume you are faster at analysing than me, so I have not tried to get
> to the bottom of these at all. Let me know if you need help reproducing
> the warnings. It's also possible that they are fixed by some other patches
> that you already sent but that are not in linux-next yet.

Thanks.  The first one is a relatively easy fix in objtool's drap
register handling.  I have a working patch for it.

The second one is a little trickier.

Instead of:

  lea	0x8(%rsp), %rsp

GCC is doing:

  lea    0x8(%rsp), %rcx
  mov    %rcx, %rsp

I don't see why GCC would do that.  We should probably ask some GCC
folks.  Objtool isn't built to track register values, so it may be a
little tricky to deal with that pattern correctly if we can't convince
GCC to fix it.

Anyway, I'm going to be on vacation next week, but I'll investigate
further when I get back.

-- 
Josh

Re: two more objtool warnings: lib/ubsan.o and fs/fs_pin.o

[Josh Poimboeuf]

On Fri, Jul 28, 2017 at 12:04:47PM -0500, Josh Poimboeuf wrote:
> On Fri, Jul 28, 2017 at 01:25:27PM +0200, Arnd Bergmann wrote:
> > Hi Josh,
> > 
> > I ran into two more warnings with the two patches you sent me in private,
> > using gcc-7.1.1:
> > 
> > lib/ubsan.o: warning: objtool: val_to_string.constprop.7()+0x97: leave
> > instruction with modified stack frame
> > .config: https://pastebin.com/dl/g04Dwdwx
> > 
> > fs/fs_pin.o: warning: objtool: pin_kill()+0x139: stack state mismatch:
> > cfa1=7+88 cfa2=7+96
> > .config: https://pastebin.com/dl/6gK6MadB
> > 
> > I assume you are faster at analysing than me, so I have not tried to get
> > to the bottom of these at all. Let me know if you need help reproducing
> > the warnings. It's also possible that they are fixed by some other patches
> > that you already sent but that are not in linux-next yet.
> 
> Thanks.  The first one is a relatively easy fix in objtool's drap
> register handling.  I have a working patch for it.
> 
> The second one is a little trickier.
> 
> Instead of:
> 
>   lea	0x8(%rsp), %rsp
> 
> GCC is doing:
> 
>   lea    0x8(%rsp), %rcx
>   mov    %rcx, %rsp
> 
> I don't see why GCC would do that.  We should probably ask some GCC
> folks.  Objtool isn't built to track register values, so it may be a
> little tricky to deal with that pattern correctly if we can't convince
> GCC to fix it.
> 
> Anyway, I'm going to be on vacation next week, but I'll investigate
> further when I get back.

I posted a patch for the first issue and I'll open a GCC bug for the
second issue.

-- 
Josh