From: Sergio Durigan Junior Date: Thu, 25 Apr 2013 12:22:26 +0000 (+0000) Subject: Andrew Haley found a bug on GDB running on ARM when using X-Git-Tag: gdb_7_6-2013-04-26-release~3 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bf057a8fbb5409ab583bb5063b083e08c87b3fcb;p=thirdparty%2Fbinutils-gdb.git 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: 2013-04-25 Andrew Haley * arm-tdep.c (BranchDest): Cast result as "unsigned long", instead of "long". gdb/testsuite/ChangeLog: 2013-04-25 Sergio Durigan Junior * gdb.arch/arm-bl-branch-dest.c: New file. * gdb.arch/arm-bl-branch-dest.exp: Likewise. --- diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 481c82faac8..20969602055 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2013-04-25 Sergio Durigan Junior + + * arm-tdep.c (BranchDest): Cast result as "unsigned long", + instead of "long". + 2013-04-25 Hui Zhu * breakpoint.c (build_target_command_list): Change loc->cond_bytecode diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c index 17246860a5a..8dc3de8e3ee 100644 --- a/gdb/arm-tdep.c +++ b/gdb/arm-tdep.c @@ -521,7 +521,7 @@ skip_prologue_function (struct gdbarch *gdbarch, CORE_ADDR pc, int is_thumb) #define sbits(obj,st,fn) \ ((long) (bits(obj,st,fn) | ((long) bit(obj,fn) * ~ submask (fn - st)))) #define BranchDest(addr,instr) \ - ((CORE_ADDR) (((long) (addr)) + 8 + (sbits (instr, 0, 23) << 2))) + ((CORE_ADDR) (((unsigned long) (addr)) + 8 + (sbits (instr, 0, 23) << 2))) /* Extract the immediate from instruction movw/movt of encoding T. INSN1 is the first 16-bit of instruction, and INSN2 is the second 16-bit of diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index d9049317fcf..5d79e898cba 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2013-04-25 Sergio Durigan Junior + + * gdb.arch/arm-bl-branch-dest.c: New file. + * gdb.arch/arm-bl-branch-dest.exp: Likewise. + 2013-04-25 Hui Zhu PR gdb/15293 diff --git a/gdb/testsuite/gdb.arch/arm-bl-branch-dest.c b/gdb/testsuite/gdb.arch/arm-bl-branch-dest.c new file mode 100644 index 00000000000..98269d0cdee --- /dev/null +++ b/gdb/testsuite/gdb.arch/arm-bl-branch-dest.c @@ -0,0 +1,29 @@ +/* This testcase is part of GDB, the GNU debugger. + + Copyright 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 . */ + +static void +foo (int a) +{ + ++a; +} + +int +main (int argc, char *argv[]) +{ + foo (10); + return 0; +} 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 00000000000..4699a4917a1 --- /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 ldflags=-Wl,-Ttext-segment=0xb0000000]] } { + return -1 +} + +if { ![runto_main] } { + return -1 +} + +gdb_test "next" "\[0-9\]+\\s+return 0;"