old-cross-binutils/gdb/testsuite/gdb.arch/arm-bl-branch-dest.exp
Sergio Durigan Junior 9991b20795 Andrew Haley found a bug on GDB running on ARM when using
--enable-64-bit-bfd.  Basically the issue happens when dealing with "bl"
instructions: GDB does branch destination calculation and (wrongly)
sign-extends the PC.  Here is a piece of his original message explaining
the problem:

>      next_pc = arm_get_next_pc (frame, get_frame_pc (frame));
>
>      /* The Linux kernel offers some user-mode helpers in a high page.  We can
>         not read this page (as of 2.6.23), and even if we could then we couldn't
>         set breakpoints in it, and even if we could then the atomic operations
>         would fail when interrupted.  They are all called as functions and return
>         to the address in LR, so step to there instead.  */
>      if (next_pc > 0xffff0000)
>        next_pc = get_frame_register_unsigned (frame, ARM_LR_REGNUM);
>
>      arm_insert_single_step_breakpoint (gdbarch, aspace, next_pc);
>
>    Unfortunately, branch destination addresses are SIGN EXTENDED to 64
>    bits.  So,
>
>    (top-gdb) p/x next_pc
>    $14 = 0xffffffffb6df2864
>
>    Which triggers the next_pc = get_frame_register_unsigned(), and we
>    cannot step into any branches because the destination PC is wrong.

Anyway, the fix is simple and Andrew himself provided it for us.  It
took a while for me to figure out how to trigger the bug (in order to
write a testcase for it), but I finally made it.

The attached patch fixes the problem (by casting to `unsigned long'
instead of just `long'), and also includes a testcase to reproduce the
issue.

gdb/ChangeLog:

2013-04-22  Andrew Haley  <aph@redhat.com>

	* arm-tdep.c (BranchDest): Cast result as "unsigned long",
	instead of "long".

gdb/testsuite/ChangeLog:

2013-04-22  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.arch/arm-bl-branch-dest.c: New file.
	* gdb.arch/arm-bl-branch-dest.exp: Likewise.
2013-04-22 09:20:33 +00:00

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# Copyright (C) 2013 Free Software Foundation, Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
if { ![istarget "arm*-*-*"] } {
verbose "Skipping ${testfile}."
return
}
standard_testfile
# We need to load the text segment in a high address. This is because
# the bug we are dealing with happened when GDB sign-extended the PC
# on ARM, causing the PC to acquire a wrong value. That's why we use
# the "-Wl,-Ttext-segment" option compile the binary.
if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} \
[list debug additional_flags=-Wl,-Ttext-segment=0xb0000000]] } {
return -1
}
if { ![runto_main] } {
return -1
}
gdb_test "next" "\[0-9\]+\\s+return 0;"