This patch supports linking powerpc64 glibc with gold, specifically
the __tls_get_addr call in elf/dl-sym.c. That call lacks marker
relocations tying it to the arg setup instructions, but the arg setup
insns are also contructed lacking the usual relocations on a Global
Dynamic TLS code sequence. So there is no chance that anything in
that sequence might be wrongly edited by the linker.
In fact, the aim of linking glibc could have been supported by simply
omitting the error whenever TLS optimisation is disabled, as it is
when linking a shared library. The patch goes further than that,
disabling TLS GD and LD sequence optimisation on a per-object basis
for object files lacking marker relocs.
PR gold/27625
* powerpc.cc (Powerpc_relobj): Add no_tls_marker_, tls_marker_,
and tls_opt_error_ variables and accessors.
(Target_powerpc::Scan::local, global): Call set_tls_marker and
set_no_tls_marker for GD and LD code sequence relocations.
(Target_powerpc::Relocate::relocate): Downgrade the "lacks marker
reloc" error to a warning when safe to do so, and omit the error
entirely if not optimising TLS sequences. Do not optimise GD and
LD sequences for objects lacking marker relocs.
(Target_powerpc::relocate_relocs): Heed no_tls_marker here too.
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gold is an ELF linker. It is intended to have complete support for
ELF and to run as fast as possible on modern systems. For normal use
it is a drop-in replacement for the older GNU linker.
gold is part of the GNU binutils. See ../binutils/README for more
general notes, including where to send bug reports.
gold was originally developed at Google, and was contributed to the
Free Software Foundation in March 2008. At Google it was designed by
Ian Lance Taylor, with major contributions by Cary Coutant, Craig
Silverstein, and Andrew Chatham.
The existing GNU linker manual is intended to be accurate
documentation for features which gold supports. gold supports most of
the features of the GNU linker for ELF targets. Notable
omissions--features of the GNU linker not currently supported in
gold--are:
* MRI compatible linker scripts
* cross-reference reports (--cref)
* various other minor options
Notes on the code
=================
These are some notes which may be helpful to people working on the
source code of gold itself.
gold is written in C++. It is a GNU program, and therefore follows
the GNU formatting standards as modified for C++. Source documents in
order of decreasing precedence:
http://www.gnu.org/prep/standards/
http://gcc.gnu.org/onlinedocs/libstdc++/manual/source_code_style.html
http://www.zembu.com/eng/procs/c++style.html
The linker is intended to have complete support for cross-compilation,
while still supporting the normal case of native linking as fast as
possible. In order to do this, many classes are actually templates
whose parameter is the ELF file class (e.g., 32 bits or 64 bits). The
C++ code is the same, but we don't pay the execution time cost of
always using 64-bit integers if the target is 32 bits. Many of these
class templates also have an endianness parameter: true for
big-endian, false for little-endian.
The linker is multi-threaded. The Task class represents a single unit
of work. Task objects are stored on a single Workqueue object. Tasks
communicate via Task_token objects. Task_token objects are only
manipulated while holding the master Workqueue lock. Relatively few
mutexes are used.
Build requirements
==================
The gold source code uses templates heavily. Building it requires a
recent version of g++. g++ 4.0.3 and 4.1.3 are known to work. g++
3.2, 3.4.3, and 4.1.2 are known to fail.
The linker script parser uses features which are only in newer
versions of bison. bison 2.3 is known to work. bison 1.26 is known
to fail. If you are building gold from an official binutils release,
the bison output should already be included.
Copyright (C) 2012-2021 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
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