Re: 2.6.11-rc3: Kylix application no longer works?

[Andrew Morton <akpm@osdl.org>]

Stephen Hemminger <shemminger@osdl.org> wrote:
>
> On Tue, 8 Feb 2005 18:51:06 +0100
> Pavel Machek <pavel@ucw.cz> wrote:
> 
> > Hi!
> > 
> > > I wonder if reverting the patch will restore the old behaviour?
> > 
> > This seems to be minimal fix to get Kylix application back to the
> > working state... Maybe it is good idea for 2.6.11?
> > 
> > Signed-off-by: Pavel Machek <pavel@suse.cz>
> > 								Pavel
> > 
> > --- clean/fs/binfmt_elf.c	2005-02-03 22:27:19.000000000 +0100
> > +++ linux/fs/binfmt_elf.c	2005-02-08 18:46:38.000000000 +0100
> > @@ -803,11 +803,8 @@
> >  				nbyte = ELF_MIN_ALIGN - nbyte;
> >  				if (nbyte > elf_brk - elf_bss)
> >  					nbyte = elf_brk - elf_bss;
> > -				if (clear_user((void __user *) elf_bss + load_bias, nbyte)) {
> > -					retval = -EFAULT;
> > -					send_sig(SIGKILL, current, 0);
> > -					goto out_free_dentry;
> > -				}
> > +				if (clear_user((void __user *) elf_bss + load_bias, nbyte))
> > +					printk(KERN_ERR "Error clearing BSS, wrong ELF executable? (Kylix?!)\n");
> 
> do once or rate limit rather than log spamming.

We could just remove the printk and stick a comment over it.  If the
application later tries to access the not-there pages then it'll just
fault.

However I worry if there is some way in which we can leave unzeroed memory
accessible to the application, although it's hard to see how that could
happen.

Daniel, Pavel cruelly chopped you off the Cc when replying.  What's your
diagnosis on the below?



Begin forwarded message:

Date: Tue, 8 Feb 2005 23:27:59 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: 2.6.11-rc3: Kylix application no longer works?


Hi!

> > > I wonder if reverting the patch will restore the old behaviour?
> > 
> > This seems to be minimal fix to get Kylix application back to the
> > working state... Maybe it is good idea for 2.6.11?
> 
> Why does clearing the BSS fail?  Are the program headers bogus?
> (readelf -l).

No idea, probably yes. Here's readelf -l result:

								Pavel

Elf file type is EXEC (Executable file)
Entry point 0x80614b4
There are 5 program headers, starting at offset 52

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  PHDR           0x000034 0x08048034 0x08048034 0x000a0 0x000a0 R E 0x4
  INTERP         0x0000d4 0x080480d4 0x080480d4 0x00013 0x00013 R   0x1
      [Requesting program interpreter: /lib/ld-linux.so.2]
  LOAD           0x000000 0x08048000 0x08048000 0xb7354 0x1b7354 R E 0x1000
  LOAD           0x0b7354 0x08200354 0x08200354 0x1e3e4 0x1f648 RW  0x1000
  DYNAMIC        0x0d56a0 0x0821e6a0 0x0821e6a0 0x00098 0x00098 RW  0x4

 Section to Segment mapping:
  Segment Sections...
   00     
   01     .interp 
   02     .interp .dynsym .dynstr .hash .rel.plt .plt .text borland.ressym borland.resstr borland.reshash borland.resdata borland.resspare 
   03     .data .rodata .got .dynamic .bss 
   04     .dynamic 


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