binutils-gdb modified for the FreeChainXenon project
cc59d02b90
This commit is part of a series which aims to share more of the target
description creation between GDB and gdbserver for x86/Linux.
After some refactoring earlier in this series the shared
x86_linux_tdesc_for_tid function was added into nat/x86-linux-tdesc.c.
However, this function still relies on amd64_linux_read_description
and i386_linux_read_description which are implemented separately for
both gdbserver and GDB. Given that at their core, all these functions
do is:
1. take an xcr0 value as input,
2. mask out some feature bits,
3. look for a cached pre-generated target description and return it
if found,
4. if no cached target description is found then call either
amd64_create_target_description or
i386_create_target_description to create a new target
description, which is then added to the cache. Return the newly
created target description.
The inner functions amd64_create_target_description and
i386_create_target_description are already shared between GDB and
gdbserver (in the gdb/arch/ directory), so the only thing that
the *_read_description functions really do is add the caching layer,
and it feels like this really could be shared.
However, we have a small problem.
Despite using the same {amd64,i386}_create_target_description
functions in both GDB and gdbserver to create the target descriptions,
on the gdbserver side we cache target descriptions based on a reduced
set of xcr0 feature bits.
What this means is that, in theory, different xcr0 values can map to
the same cache entry, which could result in the wrong target
description being used.
However, I'm not sure if this can actually happen in reality. Within
gdbserver we already split the target description cache based on i386,
amd64, and x32. I suspect within a given gdbserver session we'll only
see at most one target description for each of these.
The cache conflicting problem is caused by xcr0_to_tdesc_idx, which
maps an xcr0 value to a enum x86_linux_tdesc value, and there are only
7 usable values in enum x86_linux_tdesc.
In contrast, on the GDB side there are 64, 32, and 16 cache slots for
i386, amd64, and x32 respectively.
On the GDB side it is much more important to cache things correctly as
a single GDB session might connect to multiple different remote
targets, each of which might have slightly different x86
architectures.
And so, if we want to merge the target description caching between GDB
and gdbserver, then we need to first update gdbserver so that it
caches in the same way as GDB, that is, it needs to adopt a mechanism
that allows for the same number of cache slots of each of i386, amd64,
and x32. In this way, when the caching is shared, GDB's behaviour
will not change.
Unfortunately it's a little more complex than that due to the in
process agent (IPA).
When the IPA is in use, gdbserver sends a target description index to
the IPA, and the IPA uses this to find the correct target description
to use, the IPA having first generated every possible target
description.
Interestingly, there is certainly a bug here which results from only
having 7 values in enum x86_linux_tdesc. As multiple possible target
descriptions in gdbserver map to the same enum x86_linux_tdesc value,
then, when the enum x86_linux_tdesc value is sent to the IPA there is
no way for gdbserver to know that the IPA will select the correct
target description. This bug will get fixed by this commit.
** START OF AN ASIDE **
Back in the day I suspect this approach of sending a target
description index made perfect sense. However since this commit:
commit
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| bfd | ||
| binutils | ||
| config | ||
| contrib | ||
| cpu | ||
| elfcpp | ||
| etc | ||
| gas | ||
| gdb | ||
| gdbserver | ||
| gdbsupport | ||
| gnulib | ||
| gold | ||
| gprof | ||
| gprofng | ||
| include | ||
| ld | ||
| libbacktrace | ||
| libctf | ||
| libdecnumber | ||
| libiberty | ||
| libsframe | ||
| opcodes | ||
| readline | ||
| sim | ||
| texinfo | ||
| zlib | ||
| .cvsignore | ||
| .editorconfig | ||
| .gitattributes | ||
| .gitignore | ||
| .pre-commit-config.yaml | ||
| ar-lib | ||
| ChangeLog | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| COPYING | ||
| COPYING.LIB | ||
| COPYING.LIBGLOSS | ||
| COPYING.NEWLIB | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| depcomp | ||
| djunpack.bat | ||
| install-sh | ||
| libtool.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| lt~obsolete.m4 | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| makefile.vms | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| multilib.am | ||
| README | ||
| README-maintainer-mode | ||
| SECURITY.txt | ||
| setup.com | ||
| src-release.sh | ||
| symlink-tree | ||
| test-driver | ||
| ylwrap | ||
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.