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RFC: Add STO_COPY (Re: Copy relocation and protected symbol don't work together)


On Thu, Mar 27, 2003 at 04:37:53PM -0800, H. J. Lu wrote:
> On Wed, Mar 26, 2003 at 04:11:14PM -0800, H. J. Lu wrote:
> > On Wed, Mar 26, 2003 at 01:40:25PM -0800, H. J. Lu wrote:
> > > On Wed, Mar 26, 2003 at 12:29:09PM -0800, H. J. Lu wrote:
> > > > glibc/ld don't handle addresss of some protected symbols right. Here is
> > > > a testcase for glibc. I am not certain where the bug is. It could be
> > > > in glibc and/or ld.
> > > > 
> > > 
> > > Here is an update for my last patch. It turns out we aren't testing
> > > addresses of variables at all. We just test their values which happen
> > > to be addresses of some strings. This patch fixes the testcase. It
> > > is a glibc bug. I will post a patch later.
> > > 
> > 
> > The bug is quite tricky. Here is a testcase:
> > 
> > # make
> > gcc -O -c main.c
> > gcc -O -fPIC -c shared.c
> > gcc -shared -o libfoo.so  shared.o
> > gcc -o foo  main.o libfoo.so -Wl,-rpath,.
> > for f in foo; do echo "Running: $f"; ./$f; \
> >   if [ $? != 0 ]; then echo Failed; fi; done
> > Running: foo
> > Data address: 0x8049924 != Data address from DSO: 0x400187f4
> > Data: 100 != Data from DSO: 10
> > 
> > The problem is for a symbol with copy relocation, the main executable
> > has
> > 
> >      3: 08049924     4 OBJECT  GLOBAL DEFAULT   22 shared_data
> >     87: 08049924     4 OBJECT  GLOBAL DEFAULT   22 shared_data
> > 
> > in symbol table and
> > 
> > 08049924  00000305 R_386_COPY        08049924   shared_data
> > 
> > in relocation entries. When ld.so looks up for a protected shared_data
> > for libfoo.so, it doesn't know if the definition of shared_data in
> > executable comes from R_386_COPY by just looking at the symbol table.
> > I see we can do one of 2 things:
> > 
> > 1. ld.so checks all relocation entries for R_386_COPY.
> > 2. ld doesn't create R_386_COPY for protected definion, which will set
> > DT_TEXTREL in executable.
> > 
> > I don't like either one very much. If I have to choose, I will go with
> > #2. Is there anything else we can do? Can ld put shared_data in a
> > special .copy section so that ld.so can know it comes from R_386_COPY?
> > 
> 
> We can also add STT_COPY_OBJECT for this problem. Then the dynamic
> linker can check STT_COPY_OBJECT for definion from copy relocation.
> 
> H.J.
> ----
> bfd/
> 
> 2003-03-27  H.J. Lu <hjl at gnu dot org>
> 
> 	* elf32-i386.c (elf_i386_adjust_dynamic_symbol): Set type to
> 	STT_COPY_OBJECT for R_386_COPY relocation.
> 
> include/elf/
> 
> 2003-03-27  H.J. Lu <hjl at gnu dot org>
> 
> 	* i386.h (STT_COPY_OBJECT): New.
> 

Or we can use one bit in st_other for it.


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	0x20
 
 #define STN_UNDEF	0		/* Undefined symbol index */
 


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