RFC: STO_COPY again: Re: Copy relocation and protected symbol don't work together

["H. J. Lu" <hjl at lucon dot org>]

On Fri, Mar 28, 2003 at 06:32:23PM -0800, Roland McGrath wrote:
> I think either prohibiting such references or producing text relocs is the
> only workable answer.  If a variable is marked protected, the compiler may

Since ld doesn't know if protected symbols will be involved or
not at the run-time, are you suggesting ld should disallow copy
relocation or DT_TEXTREL for all dynamic executables in order to
properly support protected symbols? I don't think it is a good idea.

> produce GOT-relative or PC-relative references that won't have any external
> reference when linked into a DSO.  So even if the copy relocs are treated
> specially, there may be no relocation in the DSO to be pointed at the
> executable's copy.

Since it is a run-time thing, we have to always use PIC like ia64.
I don't think people will like that for x86.

> 
> I think it's also arguable that the spec says it must behave as it does
> now.  The gABI doesn't say anything about copy relocs in the specification
> of the STV_PROTECTED behavior.  I have not seen a version of a psABI that
> is as recent as the gABI that I can read; I think the old i386 one I've
> found predates the visibility additions and so obviously doesn't mention
> the issue in the specification of copy relocs.  The specification is in
> terms of the symbol table, and doesn't allow any special case in which a
> DSO's protected symbols are searched for elsewhere.

That is true. How about this patch? 0x80 in st_other has already
been used by alpha. It is like we reuse a bit in st_other. Compared
with STT_COPY_OBJECT, it doesn't have binary compatibility problem.


H.J.
---
bfd/

2003-03-28  H.J. Lu <hjl at gnu dot org>

	* elf32-i386.c (elf_i386_adjust_dynamic_symbol): Set STO_COPY
	for R_386_COPY relocation.

include/elf/

2003-03-28  H.J. Lu <hjl at gnu dot org>

	* common.h  (STO_COPY): New.

--- binutils/bfd/elf32-i386.c.copy	2003-03-07 16:44:56.000000000 -0800
+++ binutils/bfd/elf32-i386.c	2003-03-28 11:21:26.000000000 -0800
@@ -1493,6 +1493,7 @@ elf_i386_adjust_dynamic_symbol (info, h)
     {
       htab->srelbss->_raw_size += sizeof (Elf32_External_Rel);
       h->elf_link_hash_flags |= ELF_LINK_HASH_NEEDS_COPY;
+      h->other |= STO_COPY;
     }
 
   /* We need to figure out the alignment required for this symbol.  I
--- binutils/include/elf/common.h.copy	2003-01-17 09:49:09.000000000 -0800
+++ binutils/include/elf/common.h	2003-03-28 11:08:29.000000000 -0800
@@ -427,6 +427,10 @@ Foundation, Inc., 59 Temple Place - Suit
 #define ELF32_ST_VISIBILITY  ELF_ST_VISIBILITY
 #define ELF64_ST_VISIBILITY  ELF_ST_VISIBILITY
 
+/* Use one bit in the st_other field to indicate if a definition comes
+   from a copy relocation. It is used by a copy relocation against a
+   protected symbol.  */
+#define STO_COPY	0x80
 
 #define STN_UNDEF	0		/* Undefined symbol index */