807f647cac
Enable displaced stepping over a BR/BLR instruction
Displaced stepping over an instruction executes a instruction in a
scratch area and then manually fixes up the PC address to leave
execution where it would have been if the instruction were in its
original location.
The BR instruction does not need modification in order to run correctly
at a different address, but the displaced step fixup method should not
manually adjust the PC since the BR instruction sets that value already.
The BLR instruction should also avoid such a fixup, but must also have
the link register modified to point to just after the original code
location rather than back to the scratch location.
This patch adds the above functionality.
We add this functionality by modifying aarch64_displaced_step_others
rather than by adding a new visitor method to aarch64_insn_visitor.
We choose this since it seems that visitor approach is designed
specifically for PC relative instructions (which must always be modified
when executed in a different location).
It seems that the BR and BLR instructions are more like the RET
instruction which is already handled specially in
aarch64_displaced_step_others.
This also means the gdbserver code to relocate an instruction when
creating a fast tracepoint does not need to be modified, since nothing
special is needed for the BR and BLR instructions there.
Regression tests showed nothing untoward on native aarch64 (though it
took a while for me to get the testcase to account for PIE).
------#####
Original observed (mis)behaviour before was that displaced stepping over
a BR or BLR instruction would not execute the function they called.
Most easily seen by putting a breakpoint with a condition on such an
instruction and a print statement in the functions they called.
When run with the breakpoint enabled the function is not called and
"numargs called" is not printed.
When run with the breakpoint disabled the function is called and the
message is printed.
--- GDB Session
~ [15:57:14] % gdb ../using-blr
Reading symbols from ../using-blr...done.
(gdb) disassemble blr_call_value
Dump of assembler code for function blr_call_value:
...
0x0000000000400560 <+28>: blr x2
...
0x00000000004005b8 <+116>: ret
End of assembler dump.
(gdb) break *0x0000000000400560
Breakpoint 1 at 0x400560: file ../using-blr.c, line 22.
(gdb) condition 1 10 == 0
(gdb) run
Starting program: /home/matmal01/using-blr
[Inferior 1 (process 33279) exited with code 012]
(gdb) disable 1
(gdb) run
Starting program: /home/matmal01/using-blr
numargs called
[Inferior 1 (process 33289) exited with code 012]
(gdb)
Test program:
---- using-blr ----
\#include <stdio.h>
typedef int (foo) (int, int);
typedef void (bar) (int, int);
struct sls_testclass {
foo *x;
bar *y;
int left;
int right;
};
__attribute__ ((noinline))
int blr_call_value (struct sls_testclass x)
{
int retval = x.x(x.left, x.right);
if (retval % 10)
return 100;
return 9;
}
__attribute__ ((noinline))
int blr_call (struct sls_testclass x)
{
x.y(x.left, x.right);
if (x.left % 10)
return 100;
return 9;
}
int
numargs (__attribute__ ((unused)) int left, __attribute__ ((unused)) int right)
{
printf("numargs called\n");
return 10;
}
void
altfunc (__attribute__ ((unused)) int left, __attribute__ ((unused)) int right)
{
printf("altfunc called\n");
}
int main(int argc, char **argv)
{
struct sls_testclass x = { .x = numargs, .y = altfunc, .left = 1, .right = 2 };
if (argc > 2)
{
blr_call (x);
}
else
blr_call_value (x);
return 10;
}
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| bfd | ||
| binutils | ||
| config | ||
| contrib | ||
| cpu | ||
| elfcpp | ||
| etc | ||
| gas | ||
| gdb | ||
| gdbserver | ||
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| gnulib | ||
| gold | ||
| gprof | ||
| include | ||
| intl | ||
| ld | ||
| libctf | ||
| libdecnumber | ||
| libiberty | ||
| opcodes | ||
| readline | ||
| sim | ||
| texinfo | ||
| zlib | ||
| .cvsignore | ||
| .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.