This both makes the section layout more similar to that of the general
default for ELF and fixes (makes true) an assumption that code and
rodata is located between _init and __etext, in
libgcc/config/mmix/crti.S. Sadly, that's not actually true for ELF
(generally and for elf64mmix), where exception-tables and .rodata is
after _etext; I'm pondering what to do about that.
The original mmix simulator behavior is that memory magically appears
on access, initialized with 0, which is not preferable when chasing
bugs by throwing code the size of the gcc test-suite to the simulator.
The code in crti.S compatibly enables simulator machinery to identify
undefined memory and instead stopping the simulator with an error
(going to interactive mode for interactive runs). See
http://gcc.gnu.org/legacy-ml/gcc-patches/2012-10/msg01871.html for
more, including the mmix-sim.ch "patch file".
This fixes only one error in the gcc testsuite,
gcc.c-torture/execute/pr20621-1.c with LTO, where for some reason
gcc/lto chooses to move (writable) data that is only used to read 0 to
.rodata. An access (sufficiently far inside a block) in an
unregistered place is flagged as an invalid access.
The bpo-9m test that I had to adjust, actually exposes a wart: mmo
does not have the notion of symbol types (or sections) and the
test-case now has leading zeros at "Main" eventually leading to it
being misdiagnosed as being outside .text and .data, thus here mapped
to BFD as an absolute symbol. The test is not intended to check the
mmo symbol-type machinery, so I'm just tweaking it to be
symbol-type-neutral for "Main".
Since you have to jump through hoops to see the problem, I don't think
this commit is worth putting on the 2.35-branch.
ld:
* scripttempt/mmo.sc: Move .init first in .text output section.
* testsuite/ld-mmix/bpo-9m.d: Adjust accordingly.
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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) 2012-2020 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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