From 9991b20795a23272b07dd2214aa3ee0196b61f0b Mon Sep 17 00:00:00 2001 From: Sergio Durigan Junior Date: Mon, 22 Apr 2013 09:20:33 +0000 Subject: 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 * arm-tdep.c (BranchDest): Cast result as "unsigned long", instead of "long". gdb/testsuite/ChangeLog: 2013-04-22 Sergio Durigan Junior * gdb.arch/arm-bl-branch-dest.c: New file. * gdb.arch/arm-bl-branch-dest.exp: Likewise. --- gdb/testsuite/gdb.arch/arm-bl-branch-dest.exp | 37 +++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) create mode 100644 gdb/testsuite/gdb.arch/arm-bl-branch-dest.exp (limited to 'gdb/testsuite/gdb.arch/arm-bl-branch-dest.exp') diff --git a/gdb/testsuite/gdb.arch/arm-bl-branch-dest.exp b/gdb/testsuite/gdb.arch/arm-bl-branch-dest.exp new file mode 100644 index 0000000..1e433f3 --- /dev/null +++ b/gdb/testsuite/gdb.arch/arm-bl-branch-dest.exp @@ -0,0 +1,37 @@ +# 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 . + +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;" -- cgit v1.1