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dd09fe0d53
Commit 05c06f318fd9a112529dfc313e6512b399a645e4 enabled GDB to access
memory while threads are running. It did this by accessing
/proc/PID/task/LWP/mem.
Unfortunately, this interface is not implemented for writing in older
kernels (such as RHEL6). This means that GDB is unable to insert
breakpoints on these hosts:
$ ./gdb -q gdb -ex start
Reading symbols from gdb...
Temporary breakpoint 1 at 0x40fdd5: file ../../src/gdb/gdb.c, line 28.
Starting program: /home/rhel6/fsf/linux/gdb/gdb
Warning:
Cannot insert breakpoint 1.
Cannot access memory at address 0x40fdd5
(gdb)
Before this patch, linux_proc_xfer_memory_partial (previously called
linux_proc_xfer_partial) would return TARGET_XFER_EOF if the write to
/proc/PID/mem failed. [More specifically, linux_proc_xfer_partial
would not "bother for one word," but the effect is the essentially
same.]
This status was checked by linux_nat_target::xfer_partial, which would
then fallback to using ptrace to perform the operation.
This is the specific hunk that removed the fallback:
- xfer = linux_proc_xfer_partial (object, annex, readbuf, writebuf,
- offset, len, xfered_len);
- if (xfer != TARGET_XFER_EOF)
- return xfer;
+ return linux_proc_xfer_memory_partial (readbuf, writebuf,
+ offset, len, xfered_len);
+ }
return inf_ptrace_target::xfer_partial (object, annex, readbuf, writebuf,
offset, len, xfered_len);
This patch makes linux_nat_target::xfer_partial go straight to writing
memory via ptrace if writing via /proc/pid/mem is not possible in the
running kernel, enabling GDB to insert breakpoints on these older
kernels. Note that a recent patch changed the return status from
TARGET_XFER_EOF to TARGET_XFER_E_IO.
Tested on {unix,native-gdbserver,native-extended-gdbserver}/-m{32,64}
on x86_64, s390x, aarch64, and ppc64le.
Change-Id: If1d884278e8c4ea71d8836bedd56e6a6c242a415
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.