Re: A patch for default version and archive

[Ian Lance Taylor <ian at zembu dot com>]

   Date: Mon, 20 Nov 2000 11:41:33 -0800
   From: "H . J . Lu" <hjl@valinux.com>

   On Mon, Nov 20, 2000 at 10:44:31AM -0800, Ian Lance Taylor wrote:
   >    Date: Sat, 18 Nov 2000 18:17:59 -0800
   >    From: "H . J . Lu" <hjl@valinux.com>
   > 
   >    Say you want to override "open" in libc.so:
   > 
   >    # objdump --dynamic-sym /lib/libc.so.6 | grep GLIBC| grep " open$"
   >    000d8d80  w   DF .text  00000040  GLIBC_2.0   open
   >    # objdump --dynamic-sym /usr/lib/lib*.so | grep GLIBC | grep " open$"
   >    .....
   >    00000000      DF *UND*  0000003d  GLIBC_2.0   open
   > 
   >    As you can see, many DSOs in /usr/lib have "open" bound to version
   >    "GLIBC_2.0". Since GLIBC_2.0 is the default version, by providing your
   >    own implementation of "open", all refereneces to "open" version
   >    "GLIBC_2.0" will be resolved to your "open" without version. That is
   >    exactly what happens if there is no symbol versioning.
   > 
   > Yes, but those references to open were written as references to open,
   > not as references to open version GLIBC_2.0.  The program linker added

   See

   00000000      DF *UND*  0000003d  GLIBC_2.0   open
				     ^^^^^^^^^

   "open" IS bound to "open" with vesion "GLIBC_2.0". That is how symbol
   versioning works. Later, if we want to introduce a new "open", say
   open () with O_LARGEFILE by default, we can make the new "open" with
   version "GLIBC_2.3". But the reference of

   00000000      DF *UND*  0000003d  GLIBC_2.0   open

   will be bound to "open" with vesion "GLIBC_2.0" if its definiton is
   available, not the new default definiton of "open" with version
   "GLIBC_2.3". Otherwise, you will get a run-time error.

   Basically, every glibc symbol reference in a shared library built with
   -lc is bound to a specific version. At the link time, some are bound to
   a default vesioned definiton and some are bound to non-default vesioned
   definiton. But at the run-time, they make no difference. They are all
   bound to a specific version.

I believe that what we are discussing here is whether users should be
permitted to write references to specific versions in object files.

Here is what I wrote, quoted above: ``Yes, but those references to
open were written as references to open, not as references to open
version GLIBC_2.0.''

I don't see anything in what you wrote that responds to what I said.
I agree that what you say is true.  But I don't see why it is
relevant.  If you find what I wrote to be unclear, please let me know
and I will try to clarify it.

Ian