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While investigating a displaced stepping issue I wanted an easy way to see what GDB thought the original instruction was, and what instruction GDB replaced that with when performing the displaced step. We do print out the address that is being stepped, so I can track down the original instruction, I just need to go find the information myself. And we do print out the bytes of the new instruction, so I can figure out what the replacement instruction was, but it's not really easy. Also, the code that prints the bytes of the replacement instruction only prints 4 bytes, which clearly isn't always going to be correct. In this commit I remove the existing code that prints the bytes of the replacement instruction, and add two new blocks of code to displaced_step_prepare_throw. This new code prints the original instruction, and the replacement instruction. In each case we print both the bytes that make up the instruction and the completely disassembled instruction. Here's an example of what the output looks like on x86-64 (this is with 'set debug displaced on'). The two interesting lines contain the strings 'original insn' and 'replacement insn': (gdb) step [displaced] displaced_step_prepare_throw: displaced-stepping 2892655.2892655.0 now [displaced] displaced_step_prepare_throw: original insn 0x401030: ff 25 e2 2f 00 00 jmp *0x2fe2(%rip) # 0x404018 <puts@got.plt> [displaced] prepare: selected buffer at 0x401052 [displaced] prepare: saved 0x401052: 1e fa 31 ed 49 89 d1 5e 48 89 e2 48 83 e4 f0 50 [displaced] fixup_riprel: %rip-relative addressing used. [displaced] fixup_riprel: using temp reg 2, old value 0x7ffff7f8a578, new value 0x401036 [displaced] amd64_displaced_step_copy_insn: copy 0x401030->0x401052: ff a1 e2 2f 00 00 68 00 00 00 00 e9 e0 ff ff ff [displaced] displaced_step_prepare_throw: prepared successfully thread=2892655.2892655.0, original_pc=0x401030, displaced_pc=0x401052 [displaced] displaced_step_prepare_throw: replacement insn 0x401052: ff a1 e2 2f 00 00 jmp *0x2fe2(%rcx) [displaced] finish: restored 2892655.2892655.0 0x401052 [displaced] amd64_displaced_step_fixup: fixup (0x401030, 0x401052), insn = 0xff 0xa1 ... [displaced] amd64_displaced_step_fixup: restoring reg 2 to 0x7ffff7f8a578 0x00007ffff7e402c0 in puts () from /lib64/libc.so.6 (gdb) One final note. For many targets that support displaced stepping (in fact all targets except ARM) the replacement instruction is always a single instruction. But on ARM the replacement could actually be a series of instructions. The debug code tries to handle this by disassembling the entire displaced stepping buffer. Obviously this might actually print more than is necessary, but there's (currently) no easy way to know how many instructions to disassemble; that knowledge is all locked in the architecture specific code. Still I don't think it really hurts, if someone is looking at this debug then hopefully they known what to expect. Obviously we can imagine schemes where the architecture specific displaced stepping code could communicate back how many bytes its replacement sequence was, and then our debug print code could use this to limit the disassembly. But this seems like a lot of effort just to save printing a few additional instructions in some debug output. I'm not proposing to do anything about this issue for now. Approved-By: Simon Marchi <simon.marchi@efficios.com> |
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bfd | ||
binutils | ||
config | ||
contrib | ||
cpu | ||
elfcpp | ||
etc | ||
gas | ||
gdb | ||
gdbserver | ||
gdbsupport | ||
gnulib | ||
gold | ||
gprof | ||
gprofng | ||
include | ||
intl | ||
ld | ||
libbacktrace | ||
libctf | ||
libdecnumber | ||
libiberty | ||
libsframe | ||
opcodes | ||
readline | ||
sim | ||
texinfo | ||
zlib | ||
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.gitignore | ||
ar-lib | ||
ChangeLog | ||
compile | ||
config-ml.in | ||
config.guess | ||
config.rpath | ||
config.sub | ||
configure | ||
configure.ac | ||
COPYING | ||
COPYING3 | ||
COPYING3.LIB | ||
COPYING.LIB | ||
COPYING.LIBGLOSS | ||
COPYING.NEWLIB | ||
depcomp | ||
djunpack.bat | ||
install-sh | ||
libtool.m4 | ||
lt~obsolete.m4 | ||
ltgcc.m4 | ||
ltmain.sh | ||
ltoptions.m4 | ||
ltsugar.m4 | ||
ltversion.m4 | ||
MAINTAINERS | ||
Makefile.def | ||
Makefile.in | ||
Makefile.tpl | ||
makefile.vms | ||
missing | ||
mkdep | ||
mkinstalldirs | ||
move-if-change | ||
multilib.am | ||
README | ||
README-maintainer-mode | ||
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.