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Re: [PATCH 5/7] elf: Enable relro for static build


* Adhemerval Zanella:

> The code is similar to the one at rtld.c, where its check for the
> PT_GNU_RELRO header values from program headers and call
> _dl_protected_relro with the updated l_relro_{addr,size} values.

This is not the actual code that does RELRO in most cases, it's only
used with prelink.  _dl_relocate_object is what is used.

> diff --git a/elf/dl-support.c b/elf/dl-support.c
> index 5526d5ee6e..bdb5c2ae91 100644
> --- a/elf/dl-support.c
> +++ b/elf/dl-support.c
> @@ -367,14 +367,24 @@ _dl_non_dynamic_init (void)
>    if (_dl_platform != NULL)
>      _dl_platformlen = strlen (_dl_platform);
>  
> -  /* Scan for a program header telling us the stack is nonexecutable.  */
>    if (_dl_phdr != NULL)
> -    for (uint_fast16_t i = 0; i < _dl_phnum; ++i)
> -      if (_dl_phdr[i].p_type == PT_GNU_STACK)
> +    for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
> +      switch (ph->p_type)
>  	{
> -	  _dl_stack_flags = _dl_phdr[i].p_flags;
> +	/* Check if the stack is nonexecutable.  */
> +	case PT_GNU_STACK:
> +	  _dl_stack_flags = ph->p_flags;
> +	  break;
> +
> +	case PT_GNU_RELRO:
> +	  _dl_main_map.l_relro_addr = ph->p_vaddr;
> +	  _dl_main_map.l_relro_size = ph->p_memsz;
>  	  break;
>  	}
> +
> +  /* Setup relro on the binary itself.  */
> +  if (_dl_main_map.l_relro_size)
> +    _dl_protect_relro (&_dl_main_map);

Please use an explicit comparison with != 0.

I have a test case for this which I can post.  Somewhat bizarrely,
full RELRO for statically linked binaries requires linking with -z now.


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