| Summary: | Gold linker does not respect --dynamic-list option | ||
|---|---|---|---|
| Product: | binutils | Reporter: | Kevin Funk <kfunk> |
| Component: | gold | Assignee: | Cary Coutant <ccoutant> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | ccoutant |
| Priority: | P2 | ||
| Version: | 2.21 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | ||
| Attachments: |
Test case
Test case - command line output |
||
Created attachment 6155 [details]
Test case - command line output
Bump. Anyone working on that? > Bump. Anyone working on that?
Sorry, no one that I know of.
Gold's implementation of --dynamic-list seems to do nothing more than force the linker to create a dynamic symbol table entry for it -- it does not undo the effect of -Bsymbolic or protected visibility. My interpretation of the Gnu ld manual is that gold is in fact wrong here.
The fix should be a simple patch to Symbol::is_preemptible() in symtab.h. I'll try to get a patch in soon.
-cary
It was a bit more complicated. The --dynamic-list option is actually mutually exclusive with -Bsymbolic and -Bsymbolic-functions. If a dynamic list is given, the Gnu linker makes only those symbols preemptible, and binds the remaining symbols within the library. I've changed gold to do the same thing. This is an automated email from the git hooks/post-receive script. It was
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=fd834e57ffce2f5dbe3443f034e68cebd63ee89a
commit fd834e57ffce2f5dbe3443f034e68cebd63ee89a
Author: Cary Coutant <ccoutant@google.com>
Date: Wed Feb 5 14:01:52 2014 -0800
Fix problems with the --dynamic-list option.
PR gold/13577 complains that even though symbols listed in
the --dynamic-list script are exported, they are still bound symbolically
if -Bsymbolic is also used. There are two underlying problems here.
First, -Bsymbolic should be overridden by --dynamic-list, since the
dynamic list provides an explicit list of symbols that are not bound
within the library, and if we go ahead and set DT_SYMBOLIC, then the
dynamic loader will bind it within the library anyway. Second, gold
did not properly identify the symbols listed in the file as preemptible.
PR gold/16530 complains that symbols listed in the --dynamic-list script
can still be garbage collected. I've fixed this by checking the symbols
as they're added to the symbol table. (Unlike the --export-dynamic-symbol
option, we can't iterate over the list, because the --dynamic-list script
can have wildcards in it.)
gold/
2014-02-05 Cary Coutant <ccoutant@google.com>
PR gold/13577
* options.cc (General_options::parse_dynamic_list):
Set have_dynamic_list_.
(General_options::General_options): Initialize have_dynamic_list_.
(General_options::finalize): Turn off -Bsymbolic and
-Bsymbolic-functions if --dynamic-list provided.
* options.h (General_options::have_dynamic_list): New function.
(General_options::have_dynamic_list_): New data member.
* symtab.h (Symbol::is_preemptible): Handle --dynamic-list
correctly.
PR gold/16530
* symtab.cc (Symbol_table::add_from_relobj): If symbol is named
in --dynamic-list, mark it.
* testsuite/Makefile.am (gc_dynamic_list_test.sh): New test case.
(dynamic_list_2): New test case.
* testsuite/Makefile.in: Regenerate.
* testsuite/dynamic_list_2.cc: New file.
* testsuite/dynamic_list_2.t: New file.
* testsuite/dynamic_list_lib1.cc: New file.
* testsuite/dynamic_list_lib2.cc: New file.
* testsuite/gc_dynamic_list_test.c: New file.
* testsuite/gc_dynamic_list_test.sh: New file.
* testsuite/gc_dynamic_list_test.t: New file.
-----------------------------------------------------------------------
Summary of changes:
gold/options.cc | 9 ++++++
gold/options.h | 7 ++++
gold/symtab.cc | 3 +-
gold/symtab.h | 10 +++++-
gold/testsuite/Makefile.am | 26 +++++++++++++++++
gold/testsuite/Makefile.in | 47 ++++++++++++++++++++++++++++--
gold/testsuite/dynamic_list_2.cc | 40 ++++++++++++++++++++++++++
gold/testsuite/dynamic_list_2.t | 27 +++++++++++++++++
gold/testsuite/dynamic_list_lib1.cc | 37 ++++++++++++++++++++++++
gold/testsuite/dynamic_list_lib2.cc | 49 ++++++++++++++++++++++++++++++++
gold/testsuite/gc_dynamic_list_test.c | 34 ++++++++++++++++++++++
gold/testsuite/gc_dynamic_list_test.sh | 39 +++++++++++++++++++++++++
gold/testsuite/gc_dynamic_list_test.t | 25 ++++++++++++++++
13 files changed, 347 insertions(+), 6 deletions(-)
create mode 100644 gold/testsuite/dynamic_list_2.cc
create mode 100644 gold/testsuite/dynamic_list_2.t
create mode 100644 gold/testsuite/dynamic_list_lib1.cc
create mode 100644 gold/testsuite/dynamic_list_lib2.cc
create mode 100644 gold/testsuite/gc_dynamic_list_test.c
create mode 100755 gold/testsuite/gc_dynamic_list_test.sh
create mode 100644 gold/testsuite/gc_dynamic_list_test.t
Fixed on trunk. The master branch has been updated by Cary Coutant <ccoutant@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=e9c1bdad269c0c3352eebcc9481ed65144001b0b commit e9c1bdad269c0c3352eebcc9481ed65144001b0b Author: Cary Coutant <ccoutant@google.com> Date: Mon Feb 16 22:15:12 2015 -0800 Fix --dynamic-list so that symbols not in the list are still exported. In PR 13577, the complaint was that -Bsymbolic was overriding the binding behavior for symbols listed in the --dynamic-list by setting the DT_SYMBOLIC tag in the dynamic table. In reading the Gnu ld manual, I decided that --dynamic-list should be mutually exclusive of -Bsymbolic, and modified gold so that --dynamic-list would treat symbols listed as preemptible, and all other symbols as internally bound. I was wrong. PR 16992 shows that with --dynamic-list (and not -Bsymbolic), a symbol not listed in the dynamic list is being internally bound within the shared library, but because it's still in the dynamic symbol table, we expose it to a COPY relocation, and things go really bad from there. (I can reproduce the same failure, simply by turning on -Bsymbolic-functions with the Gnu linker. Even though the symbol is bound internally, it's still exported to the dynamic symbol table, and is exposed to a COPY relocation.) I've backed out part of the fix for PR 13577, and -Bsymbolic (or -Bsymbolic-functions) can now be used with --dynamic-list, but if the two are used together, we do not set DT_SYMBOLIC or DF_SYMBOLIC (this matches Gnu ld behavior). We now treat symbols listed in the dynamic list as premptible, but we do not automatically treat symbols not listed there as non-premptible. gold/ PR gold/13577 PR gold/16992 * layout.cc (Layout::finish_dynamic_section): Don't set DT_SYMBOLIC or DF_SYMBOLIC if --dynamic-list option is used. * options.cc (General_options::finalize): --dynamic-list is not mutually exclusive with -Bsymbolic. * symtab.h (Symbol::is_preemptible): Don't exclude dynamic symbols not listed in --dynamic-list. * testsuite/Makefile.am (dynamic_list_lib2.so): Add -Bsymbolic-functions. * testsuite/Makefile.in: Regenerate. |
Created attachment 6154 [details] Test case We encountered some problems with regards to symbols not being relocatable in DSOs. The shared libraries in our case are compiled with -Bsymbolic-functions turned on. To avoid that certain symbols are bound to the definition within the shared library we specificy the --dynamic-list option. This seems to work fine when ld.bfd is used, but does seem to be ignored when ld.gold is used instead. I've attached a small test case showing the issue. There is the source file libtest.cpp containing an symbol "foo" which in turn is called by "test_foo". The symbol "foo" is supposed to be relocatable even if compiled with -Bsymbolic. To achieve this --dynamic-list is passed, pointing to a file which declares "foo" global. When ld.bfd is in use, the resulting libtestsym.so (which is compiled with -Bsymbolic-functions -Wl,--dynamic-list=libtest_syms.txt) contains a symbol "foo" which is relocatable (checked with "objdump -D libtestsym.so | grep foo | grep plt"). When being linked by ld.gold, however, "foo" in libtestsym.so does not seem to be relocatable, as seen by the missing .PLT entry for "foo". I'm attaching the test case + command line sequence to show this problem. Note: I've also tested with latest trunk version of gold, still did not work.