Re: [PATCH] [PR gdb/21695] Fix lost line info for symbol at addr zero

[Omair Javaid <omair.javaid@linaro.org>]

On Tue, 12 Jun 2018 at 07:25, Omair Javaid <omair.javaid@linaro.org> wrote:
>
> On 28 May 2018 at 15:49, Omair Javaid <omair.javaid@linaro.org> wrote:
> > On 15 May 2018 at 19:04, Omair Javaid <omair.javaid@linaro.org> wrote:
> >> This patch fixes a unique condition where GDB fails to provide line
> >> information of symbol at address zero when code is compiled with text
> >> address zero but loaded at an offset > 0.
> >>
> >> For example lets compile following code snippet:
> >>
> >> int main() {
> >>   return 0;
> >> }
> >>
> >> gcc -O0 -g3 -nostdlib -emain -Wl,-Ttext=0x00 -o file.out file.c
> >>
> >> Start gdb and run:
> >>
> >> add-symbol-file file.out 0xffff0000
> >> info line main
> >>
> >> GDB will return error saying no line info is available for the symbol.
> >>
> >> This is a direct consequence of the fix for PR 12528 where GDB tries to ignore
> >> line table for a function which has been garbage collected by the linker.
> >>
> >> As the garbage collected symbols are sent to address zero GDB assumes a symbol
> >> actually placed at address zero as garbage collected.
> >>
> >> This was fixed with an additional check address < lowpc. But when symbol is
> >> loaded at an offset lowpc becomes lowpc + offset while no offset is added to
> >> address rather final symbol address is calculated based on baseaddr and address
> >> added together. So in case where symbols are loaded at an offset the condition
> >> address < lowpc will always return true.
> >>
> >> This patch fixes this by comparing address against a non offset lowpc.
> >> This patch also adds a GDB test case to replicate this behavior.
> >>
> >> gdb:
> >>
> >> 2018-05-15  Omair Javaid  <omair.javaid@linaro.org>
> >>
> >>         PR gdb/21695
> >>         * dwarf2read.c (lnp_state_machine::check_line_address): Update declaration.
> >>         (dwarf_decode_lines_1): Adjust.
> >>
> >> gdb/testsuite:
> >>
> >> 2018-05-15  Omair Javaid  <omair.javaid@linaro.org>
> >>
> >>         PR gdb/21695
> >>         * gdb.base/infoline-reloc-main-from-zero.exp: New test.
> >>         * gdb.base/infoline-reloc-main-from-zero.c: New file.
> >> ---
> >>  gdb/dwarf2read.c                                   |  8 ++--
> >>  .../gdb.base/infoline-reloc-main-from-zero.c       | 24 ++++++++++
> >>  .../gdb.base/infoline-reloc-main-from-zero.exp     | 51 ++++++++++++++++++++++
> >>  3 files changed, 79 insertions(+), 4 deletions(-)
> >>  create mode 100644 gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.c
> >>  create mode 100644 gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.exp
> >>
> >> diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
> >> index 575d316..b171bb2 100644
> >> --- a/gdb/dwarf2read.c
> >> +++ b/gdb/dwarf2read.c
> >> @@ -20411,7 +20411,7 @@ public:
> >>       sequence.  */
> >>    void check_line_address (struct dwarf2_cu *cu,
> >>                            const gdb_byte *line_ptr,
> >> -                          CORE_ADDR lowpc, CORE_ADDR address);
> >> +                          CORE_ADDR lowpc_minus_base, CORE_ADDR address);
> >>
> >>    void handle_set_discriminator (unsigned int discriminator)
> >>    {
> >> @@ -20755,14 +20755,14 @@ lnp_state_machine::lnp_state_machine (gdbarch *arch, line_header *lh,
> >>  void
> >>  lnp_state_machine::check_line_address (struct dwarf2_cu *cu,
> >>                                        const gdb_byte *line_ptr,
> >> -                                      CORE_ADDR lowpc, CORE_ADDR address)
> >> +                                      CORE_ADDR lowpc_minus_base, CORE_ADDR address)
> >>  {
> >>    /* If address < lowpc then it's not a usable value, it's outside the
> >>       pc range of the CU.  However, we restrict the test to only address
> >>       values of zero to preserve GDB's previous behaviour which is to
> >>       handle the specific case of a function being GC'd by the linker.  */
> >>
> >> -  if (address == 0 && address < lowpc)
> >> +  if (address == 0 && address < lowpc_minus_base)
> >>      {
> >>        /* This line table is for a function which has been
> >>          GCd by the linker.  Ignore it.  PR gdb/12528 */
> >> @@ -20857,7 +20857,7 @@ dwarf_decode_lines_1 (struct line_header *lh, struct dwarf2_cu *cu,
> >>                     line_ptr += bytes_read;
> >>
> >>                     state_machine.check_line_address (cu, line_ptr,
> >> -                                                     lowpc, address);
> >> +                                                     lowpc - baseaddr, address);
> >>                     state_machine.handle_set_address (baseaddr, address);
> >>                   }
> >>                   break;
> >> diff --git a/gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.c b/gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.c
> >> new file mode 100644
> >> index 0000000..8902051
> >> --- /dev/null
> >> +++ b/gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.c
> >> @@ -0,0 +1,24 @@
> >> +/* This testcase is part of GDB, the GNU debugger.
> >> +
> >> +   Copyright 2011-2018 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/>.  */
> >> +
> >> +// Test case for PR gdb/21695
> >> +
> >> +int
> >> +main ()
> >> +{
> >> +  return 0;
> >> +}
> >> diff --git a/gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.exp b/gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.exp
> >> new file mode 100644
> >> index 0000000..68564688
> >> --- /dev/null
> >> +++ b/gdb/testsuite/gdb.base/infoline-reloc-main-from-zero.exp
> >> @@ -0,0 +1,51 @@
> >> +# Copyright 2011-2018 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/>.
> >> +
> >> +# This file is part of the gdb testsuite
> >> +
> >> +#
> >> +# test running programs
> >> +#
> >> +
> >> +standard_testfile .c
> >> +
> >> +if [get_compiler_info] {
> >> +    return -1
> >> +}
> >> +
> >> +# Build executable with stripped startup code and text section starting at zero
> >> +
> >> +set opts {debug "additional_flags=-nostdlib -emain -Wl,-Ttext=0x00"}
> >> +
> >> +if {[build_executable $testfile.exp $testfile $srcfile $opts] == -1} {
> >> +    untested "failed to compile"
> >> +    return -1
> >> +}
> >> +
> >> +gdb_exit
> >> +gdb_start
> >> +gdb_reinitialize_dir $srcdir/$subdir
> >> +
> >> +# Load symbols at an offset 0xffff0000 using add-symbol-file
> >> +
> >> +gdb_test "add-symbol-file [standard_output_file ${testfile}] 0xffff000" \
> >> +    "Reading symbols from .*" \
> >> +    "add-symbol-file" \
> >> +    "add symbol table from file \".*\" at.*\\(y or n\\) " "y"
> >> +
> >> +# Check if we are able to read offset adjusted line information of main
> >> +
> >> +gdb_test "info line main" \
> >> +       "Line.*starts at address.*and ends at.*"
> >> --
> >> 2.7.4
> >>
> >
> >
> > Ping!
>
> Ping!

Ping!