[gold patch] Add --no-gnu-unique option to disable STB_GNU_UNIQUE

[gold patch] Add --no-gnu-unique option to disable STB_GNU_UNIQUE

[Cary Coutant]

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The use of STB_GNU_UNIQUE breaks a bunch of applications that expect
dlopen("lib", RTLD_LOCAL) to load "lib" in a local namespace. The
loader makes the subset of symbols that have STB_GNU_UNIQUE binding
global, regardless of the option to dlopen(), and the apps break
because of the unexpected sharing across namespaces. The attached
patch adds --[no-]gnu-unique options to control conversion of
STB_GNU_UNIQUE symbols into regular STB_GLOBAL symbols in the output
file.

OK?

-cary


	* options.h (class General_options): Add --[no-]gnu-unique options.
	* symtab.cc (Symbol_table::sized_write_globals): Convert
	STB_GNU_UNIQUE to STB_GLOBAL if --no-gnu-unique.

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2011-10-27  Cary Coutant  <ccoutant@google.com>

	* options.h (class General_options): Add --[no-]gnu-unique options.
	* symtab.cc (Symbol_table::sized_write_globals): Convert
	STB_GNU_UNIQUE to STB_GLOBAL if --no-gnu-unique.


commit 80d88be500f6328258f58e8217bd38c4e18a069f
Author: Cary Coutant <ccoutant@google.com>
Date:   Thu Oct 27 14:37:16 2011 -0700

    Add --no-gnu-unique option.

diff --git a/gold/options.h b/gold/options.h
index 2837790..9909483 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -787,6 +787,10 @@ class General_options
   DEFINE_bool(g, options::EXACTLY_ONE_DASH, '\0', false,
 	      N_("Ignored"), NULL);
 
+  DEFINE_bool(gnu_unique, options::TWO_DASHES, '\0', true,
+	      N_("Enable STB_GNU_UNIQUE symbol binding (default)"),
+	      N_("Disable STB_GNU_UNIQUE symbol binding"));
+
   DEFINE_string(soname, options::ONE_DASH, 'h', NULL,
                 N_("Set shared library name"), N_("FILENAME"));
 
diff --git a/gold/symtab.cc b/gold/symtab.cc
index a90fee4..a5ea374 100644
--- a/gold/symtab.cc
+++ b/gold/symtab.cc
@@ -2822,6 +2822,12 @@ Symbol_table::sized_write_globals(const Stringpool* sympool,
       typename elfcpp::Elf_types<size>::Elf_Addr sym_value = sym->value();
       typename elfcpp::Elf_types<size>::Elf_Addr dynsym_value = sym_value;
       elfcpp::STB binding = sym->binding();
+
+      // If --no-gnu-unique is set, change STB_GNU_UNIQUE to STB_GLOBAL.
+      if (binding == elfcpp::STB_GNU_UNIQUE
+	  && !parameters->options().gnu_unique())
+	binding = elfcpp::STB_GLOBAL;
+
       switch (sym->source())
 	{
 	case Symbol::FROM_OBJECT:

Re: [gold patch] Add --no-gnu-unique option to disable STB_GNU_UNIQUE

[Ian Lance Taylor]

Cary Coutant <ccoutant@google.com> writes:

> 	* options.h (class General_options): Add --[no-]gnu-unique options.
> 	* symtab.cc (Symbol_table::sized_write_globals): Convert
> 	STB_GNU_UNIQUE to STB_GLOBAL if --no-gnu-unique.

This is OK.

Thanks.

It seems that GNU ld should consider picking up this option as well.
The basic problem is that it is ambiguous at dlopen time whether a given
global symbol should be unique or not.  If you want to dlopen a library
to live in its own private world, using RTLD_LOCAL, then symbols should
be unique within that private world, not unique across the whole
program.  Unfortunately there is no way to specify that, and the glibc
dynamic linker currently treats STB_GNU_UNIQUE symbols as unique across
the entire link.  I suspect that the correct fix is going to be to add
another flag to dlopen.

Ian