mirror of
https://sourceware.org/git/binutils-gdb.git
synced 2024-12-27 04:52:05 +08:00
202be274a4
While working on another patch[1] I had need to touch this code in
i386-dis.c:
ins->obufp = ins->mnemonicendp;
for (i = strlen (ins->obuf) + prefix_length; i < 6; i++)
oappend (ins, " ");
oappend (ins, " ");
(*ins->info->fprintf_styled_func)
(ins->info->stream, dis_style_mnemonic, "%s", ins->obuf);
What this code does is add whitespace after the instruction mnemonic
and before the instruction operands.
The problem I ran into when working on this code can be seen by
assembling this input file:
.text
nop
retq
Now, when I disassemble, here's the output. I've replaced trailing
whitespace with '_' so that the issue is clearer:
Disassembly of section .text:
0000000000000000 <.text>:
0: 90 nop
1: c3 retq___
Notice that there's no trailing whitespace after 'nop', but there are
three spaces after 'retq'!
What happens is that instruction mnemonics are emitted into a buffer
instr_info::obuf, then instr_info::mnemonicendp is setup to point to
the '\0' character at the end of the mnemonic.
When we emit the whitespace, this is then added starting at the
mnemonicendp position. Lets consider 'retq', first the buffer is
setup like this:
'r' 'e' 't' 'q' '\0'
Then we add whitespace characters at the '\0', converting the buffer
to this:
'r' 'e' 't' 'q' ' ' ' ' ' ' '\0'
However, 'nop' is actually an alias for 'xchg %rax,%rax', so,
initially, the buffer is setup like this:
'x' 'c' 'h' 'g' '\0'
Then in NOP_Fixup we spot that we have an instruction that is an alias
for 'nop', and adjust the buffer to this:
'n' 'o' 'p' '\0' '\0'
The second '\0' is left over from the original buffer contents.
However, when we rewrite the buffer, we don't afjust mnemonicendp,
which still points at the second '\0' character.
Now, when we insert whitespace we get:
'n' 'o' 'p' '\0' ' ' ' ' ' ' ' ' '\0'
Notice the whitespace is inserted after the first '\0', so, when we
print the buffer, the whitespace is not printed.
The fix for this is pretty easy, I can change NOP_Fixup to adjust
mnemonicendp, but now a bunch of tests start failing, we now produce
whitespace after the 'nop', which the tests don't expect.
So, I could update the tests to expect the whitespace....
...except I'm not a fan of trailing whitespace, so I'd really rather
not.
Turns out, I can pretty easily update the whitespace emitting code to
spot instructions that have zero operands and just not emit any
whitespace in this case. So this is what I've done.
I've left in the fix for NOP_Fixup, I think updating mnemonicendp is
probably a good thing, though this is not really required any more.
I've then updated all the tests that I saw failing to adjust the
expected patterns to account for the change in whitespace.
[1] https://sourceware.org/pipermail/binutils/2022-April/120610.html
|
||
|---|---|---|
| bfd | ||
| binutils | ||
| config | ||
| contrib | ||
| cpu | ||
| elfcpp | ||
| etc | ||
| gas | ||
| gdb | ||
| gdbserver | ||
| gdbsupport | ||
| gnulib | ||
| gold | ||
| gprof | ||
| gprofng | ||
| include | ||
| intl | ||
| ld | ||
| libbacktrace | ||
| libctf | ||
| libdecnumber | ||
| libiberty | ||
| 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 | ||
| 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.