[PATCH/RFA] elf64-alpha: Don't put DT_PLTGOT dynamic if no PLT

[PATCH/RFA] elf64-alpha: Don't put DT_PLTGOT dynamic if no PLT

[Jason R Thorpe]

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The following was found/fixed in NetBSD's 2.11.2-based binutils
by Charles Hannum.  The problem is still present in binutils CVS.

The problem occurs when a shared object contains no external references,
and thus has no PLT.  elf64_alpha_size_dynamic_sections() inserts a
DT_PLTGOT entry anyway, which confuses the dynamic linker, resulting in
a crash.  Here is a test case:

 --- a.c ---
fred () { }
 ---

 --- b.c ---
#include <stdio.h>
#include <dlfcn.h>

extern int      fred();

main()
{
        void           *handle;
        void           *symbol;

        handle = dlopen("./a.so", RTLD_NOW);
        if (handle == NULL) {
                printf("dlopen failed");
                exit(1);
        }
        dlclose(handle);
        exit(0);
}
 ---

% /usr/local/gnu/bin/gcc -shared -o a.so a.c
% /usr/local/gnu/bin/gcc -o b b.c
% ./b
pid 1969 (b): unaligned access: va=0x16001447c pc=0x1600144dc ra=0x160026a68 sp=0x1fffff368 op=ldq
Memory fault (core dumped) 
%

(FWIW, the test case was essentially extracted from autoconf tests performed
by perl and zsh.)

The following patch fixes the problem by only adding DT_PLTGOT if there
is a PLT.

OK for mainline?

OK for 2.13 branch?

OK for 2.12 branch?

	* elf64-alpha.c (elf64_alpha_size_dynamic_sections): Only insert
	DT_PLTGOT into the dynamic section if there is a PLT.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>

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Index: elf64-alpha.c
===================================================================
RCS file: /cvs/src/src/bfd/elf64-alpha.c,v
retrieving revision 1.77
diff -c -r1.77 elf64-alpha.c
*** elf64-alpha.c	7 Jul 2002 09:10:40 -0000	1.77
--- elf64-alpha.c	18 Jul 2002 20:49:40 -0000
***************
*** 4120,4131 ****
  	    return false;
  	}
  
-       if (!add_dynamic_entry (DT_PLTGOT, 0))
- 	return false;
- 
        if (relplt)
  	{
! 	  if (!add_dynamic_entry (DT_PLTRELSZ, 0)
  	      || !add_dynamic_entry (DT_PLTREL, DT_RELA)
  	      || !add_dynamic_entry (DT_JMPREL, 0))
  	    return false;
--- 4120,4129 ----
  	    return false;
  	}
  
        if (relplt)
  	{
! 	  if (!add_dynamic_entry (DT_PLTGOT, 0)
! 	      || !add_dynamic_entry (DT_PLTRELSZ, 0)
  	      || !add_dynamic_entry (DT_PLTREL, DT_RELA)
  	      || !add_dynamic_entry (DT_JMPREL, 0))
  	    return false;

Re: [PATCH/RFA] elf64-alpha: Don't put DT_PLTGOT dynamic if no PLT

[Alan Modra]

On Thu, Jul 18, 2002 at 01:57:11PM -0700, Jason R Thorpe wrote:
> The problem occurs when a shared object contains no external references,
> and thus has no PLT.  elf64_alpha_size_dynamic_sections() inserts a
> DT_PLTGOT entry anyway, which confuses the dynamic linker, resulting in
> a crash.

So, it's really a NetBSD dynamic linker bug?

> 	* elf64-alpha.c (elf64_alpha_size_dynamic_sections): Only insert
> 	DT_PLTGOT into the dynamic section if there is a PLT.

I'm fairly certain this won't cause any problem with glibc based
systems, so the patch is OK everywhere.  Give Richard Henderson
a day or two to nak it before committing though.  Hey Richard,
why aren't you listed as binutils alpha maintainer?

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre

Re: [PATCH/RFA] elf64-alpha: Don't put DT_PLTGOT dynamic if no PLT

[Jason R Thorpe]

On Fri, Jul 19, 2002 at 08:16:59PM +0930, Alan Modra wrote:

 > On Thu, Jul 18, 2002 at 01:57:11PM -0700, Jason R Thorpe wrote:
 > > The problem occurs when a shared object contains no external references,
 > > and thus has no PLT.  elf64_alpha_size_dynamic_sections() inserts a
 > > DT_PLTGOT entry anyway, which confuses the dynamic linker, resulting in
 > > a crash.
 > 
 > So, it's really a NetBSD dynamic linker bug?

It seems more like a BFD bug, to me; it told the dynamic linker there
was a PLT when in fact there was not.  How is this not a BFD bug?

A quick random sampling of a few other ELF back-ends shows that they
also do not add DT_PLTGOT if a PLT is not present... alpha was the
odd man out.

 > > 	* elf64-alpha.c (elf64_alpha_size_dynamic_sections): Only insert
 > > 	DT_PLTGOT into the dynamic section if there is a PLT.
 > 
 > I'm fairly certain this won't cause any problem with glibc based
 > systems, so the patch is OK everywhere.  Give Richard Henderson
 > a day or two to nak it before committing though.  Hey Richard,
 > why aren't you listed as binutils alpha maintainer?

Yah, I was hoping (expecting? :-) Richard would confirm this wouldn't be
a problem for Linux systems...

Once I hear an OK from Richard, it might be a couple of days before
I check it in, though, as I'm leaving for a short vacation tomorrow.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>

Re: [PATCH/RFA] elf64-alpha: Don't put DT_PLTGOT dynamic if no PLT

[Richard Henderson]

On Fri, Jul 19, 2002 at 09:06:26AM -0700, Jason R Thorpe wrote:
>  > So, it's really a NetBSD dynamic linker bug?
> 
> It seems more like a BFD bug, to me; it told the dynamic linker there
> was a PLT when in fact there was not.  How is this not a BFD bug?

*shrug* It told the dynamic linker the address of the zero
sized PLT section.  You still want to fix the dynamic linker.

The change won't hurt anything though.


r~