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ed53e990e5
Dereferences of GOT slots with lgrl or lg for global symbols are rewritten to larl to get get rid of the extra memory access. However this is invalid for: - symbols marked for absolute addressing - symbols at odd addresses (larl can handle only even addresses) Commite6213e09ed("S/390: Prevent GOT access rewrite for certain symbols") added checks for the above. But instead of checking the address of a symbol for being halfword aligned, it tries to deduce this from whether the symbol value and section the symbol is defined in are halfword aligned. The way it is done has two issues: 1. The use of bfd_section_from_elf_index to obtain the section the symbol is defined in may not return the one that remains in the output. For instance for COMDAT sections getting deduplicated the section retrieved using bfd_section_from_elf_index may not be the same as h->root.u.def.section. If COMDAT sections of same group signature have different alignment properties the wrong one may be checked. This may then lead to an erroneous rewrite of lgrl %rX, sym@GOTENT to larl %rX, sym, although the symbol in the remaining section is not properly aligned, triggering an "relocation for misaligned symbol" error at link-time. This may for instance occur when mixing C++ modules compiled with GCC and Clang, as GCC emits a 2-byte alignment and Clang a 1-byte alignment for COMDAT sections containing type information: $ cat sample.cpp #include <typeinfo> struct A {}; const std::type_info &q() { return typeid(A); } $ g++ -c sample.cpp -o sample_gcc.o $ clang++ -c sample.cpp -o sample_clang.o $ readelf -WS sample_gcc.o sample_clang.o Produces (reformatted and reduced): File Name Off Size ES Flg Lk Inf Al sample_gcc.o .rodata._ZTS1A 000080 000004 00 AG 0 0 2 sample_clang.o .rodata._ZTS1A 000058 000003 00 AG 0 0 1 2. The symbol may end up at an even address, if both the symbol value and the section defining the symbol are 1-byte aligned. While this does not trigger an error, it fails an opportunity to rewrite a GOT access. In a Linux Kernel build this causes ~15k GOT accesses using lgrl to be skipped to be rewritten to larl. Resolve both issues by simply checking whether the symbol address is halfword aligned. Do not check the symbol value nor section defining the symbol for halfword alignment. bfd/ PR ld/32969 * elf64-s390.c (elf_s390_relocate_section): Only rewrite lgrl/lg from GOT to larl if symbol address is halfword aligned. ld/testsuite/ PR ld/32969 * ld-s390/s390.exp (pr32969_64-1, pr32969_64-2): Add tests for rewrite of GOT access when COMDAT section deduplication is involved. * ld-s390/pr32969_64-1.dd: New test for rewrite of GOT access when COMDAT section deduplication is involved. * ld-s390/pr32969_64-2.dd: Likewise. * ld-s390/pr32969a.s: Likewise. * ld-s390/pr32969b.s: Likewise. * ld-s390/pr32969c.s: Likewise. Bug: https://sourceware.org/PR32969 Fixes:e6213e09ed("S/390: Prevent GOT access rewrite for certain symbols") Reported-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Jens Remus <jremus@linux.ibm.com>
README for LD
This is the GNU linker. It is distributed with other "binary
utilities" which should be in ../binutils. See ../binutils/README for
more general notes, including where to send bug reports.
There are many features of the linker:
* The linker uses a Binary File Descriptor library (../bfd)
that it uses to read and write object files. This helps
insulate the linker itself from the format of object files.
* The linker supports a number of different object file
formats. It can even handle multiple formats at once:
Read two input formats and write a third.
* The linker can be configured for cross-linking.
* The linker supports a control language.
* There is a user manual (ld.texi), as well as the
beginnings of an internals manual (ldint.texi).
Installation
============
See ../binutils/README.
If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.
To build just the linker, make the target all-ld from the top level
directory (one directory above this one).
Porting to a new target
=======================
See the ldint.texi manual.
Reporting bugs etc
===========================
See ../binutils/README.
Known problems
==============
The Solaris linker normally exports all dynamic symbols from an
executable. The GNU linker does not do this by default. This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets). This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl. You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.
HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly. The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages. There are various
workarounds to this:
* Build and install bash, and build with "make SHELL=bash".
* Update to a version of HP/UX with a working shell (e.g., 9.05).
* Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
emulparams script used exports any shell variables it sets.
Copyright (C) 2012-2025 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.