binutils-gdb modified for the FreeChainXenon project
96619f154a
In the following commit I ran into a problem. The next commit aims to improve GDB's handling of the main executable being a file on a remote target (i.e. one with a 'target:' prefix). To do this I have replaced a system 'stat' call with a bfd_stat call. However, doing this caused a regression in gdb.base/attach.exp. The problem is that the bfd library caches open FILE* handles for bfd objects that it has accessed, which is great for short-lived, non interactive programs (e.g. the assembler, or objcopy, etc), however, for GDB this caching causes us a problem. If we open the main executable as a bfd then the bfd library will cache the open FILE*. If some time passes, maybe just sat at the GDB prompt, or with the inferior running, and then later we use bfd_stat to check if the underlying, on-disk file has changed, then the bfd library will actually use fstat on the underlying file descriptor. This is of course slightly different than using system stat on with the on-disk file name. If the on-disk file has changed then system stat will give results for the current on-disk file. But, if the bfd cache is still holding open the file descriptor for the original on-disk file (from before the change) then fstat will return a result based on the original file, and so show no change as having happened. This is a known problem in GDB, and so far this has been solved by scattering bfd_cache_close_all() calls throughout GDB. But, as I said, in the next commit I've made a change and run into a problem (gdb.base/attach.exp) where we are apparently missing a bfd_cache_close_all() call. Now I could solve this problem by adding a bfd_cache_close_all() call before the bfd_stat call that I plan to add in the next commit, that would for sure solve the problem, but feels a little crude. Better I think would be to track down where the bfd is being opened and add a corresponding bfd_cache_close_all() call elsewhere in GDB once we've finished doing whatever it is that caused us to open the bfd in the first place. This second solution felt like the better choice, so I tracked the problem down to elf_locate_base and fixed that. But that just exposed another problem in gdb_bfd_map_section which was also re-opening the bfd, so I fixed this (with another bfd_cache_close_all() call), and that exposed another issue in gdbarch_lookup_osabi... and at this point I wondered if I was approaching this problem the wrong way... .... And so, I wonder, is there a _better_ way to handle these bfd_cache_close_all() calls? I see two problems with the current approach: 1. It's fragile. Folk aren't always aware that they need to clear the bfd cache, and this feels like something that is easy to overlook in review. So adding new code to GDB can innocently touch a bfd, which populates the cache, which will then be a bug that can lie hidden until an on-disk file just happens to change at the wrong time ... and GDB fails to spot the change. Additionally, 2. It's in efficient. The caching is intended to stop the bfd library from continually having to re-open the on-disk file. If we have a function that touches a bfd then often that function is the obvious place to call bfd_cache_close_all. But if a single GDB command calls multiple functions, each of which touch the bfd, then we will end up opening and closing the same on-disk file multiple times. It feels like we would be better postponing the bfd_cache_close_all call until some later point, then we can benefit from the bfd cache. So, in this commit I propose a new approach. We now clear the bfd cache in two places: (a) Just before we display a GDB prompt. We display a prompt after completing a command, and GDB is about to enter an idle state waiting for further input from the user (or in async mode, for an inferior event). If while we are in this idle state the user changes the on-disk file(s) then we would like GDB to notice this the next time it leaves its idle state, e.g. the next time the user executes a command, or when an inferior event arrives, (b) When we resume the inferior. In synchronous mode, resuming the inferior is another time when GDB is blocked and sitting idle, but in this case we don't display a prompt. As with (a) above, when an inferior event arrives we want GDB to notice any changes to on-disk files. It turns out that there are existing observers for both of these cases (before_prompt and target_resumed respectively), so my initial thought was that I should attach to these observers in gdb_bfd.c, and in both cases call bfd_cache_close_all(). And this does indeed solve the gdb.base/attach.exp problem that I see with the following commit. However, I see a problem with this solution. Both of the observers I'm using are exposed through the Python API as events that a user can hook into. The user can potentially run any GDB command (using gdb.execute), so Python code might end up causing some bfds to be reopened, and inserted into the cache. To solve this one solution would be to add a bfd_cache_close_all() call into gdbpy_enter::~gdbpy_enter(). Unfortunately, there's no similar enter/exit object for Guile, though right now Guile doesn't offer the same event API, so maybe we could just ignore that problem... but this doesn't feel great. So instead, I think a better solution might be to not use observers for the bfd_cache_close_all() calls. Instead, I'll call bfd_cache_close_all() directly from core GDB after we've notified the before_prompt and target_resumed observers, this was we can be sure that the cache is cleared after the observers have run, and before GDB enters an idle state. This commit also removes all of the other bfd_cache_close_all() calls from GDB. My claim is that these are no longer needed. Approved-By: Tom Tromey <tom@tromey.com> |
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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 | ||
| 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.