Re: [PATCH v4] [PR gdb/27614] gdb-add-index fails on symlinks.

[Lancelot SIX via Gdb-patches <gdb-patches@sourceware.org>]

Hi,

Kindly pinging.

Lancelot.

On Mon, Mar 29, 2021 at 09:52:24PM +0100, Lancelot SIX wrote:
> Since V3:
> 	- Do net rely on GDB's maintenance commands to resolve
> 	symlinks, revert to using readlink while maximizing portability.
> 
> Since V2:
> 	- Use GDB to follow symlink instead of readlink. Unlike
> 	readlink, GDB is guaranteed to be available.
> 
> Since V1:
> 	- Replace '&>/dev/null' with '>/dev/null 2>&1'
> 
> --
> 
> PR 27614 shows that gdb-add-index fails to generate the index when its
> argument is a symlink.
> 
> The following one liner illustrates the reported problem:
> 
>         $ echo 'int main(){}'|gcc -g -x c -;ln -s a.out symlink;gdb-add-index symlink
>         gdb-add-index: No index was created for symlink
>         gdb-add-index: [Was there no debuginfo? Was there already an index?]
>         $ ls -l
>         -rwxr-xr-x 1 25712 Mar 19 23:05 a.out*
>         -rw------- 1  8277 Mar 19 23:05 a.out.gdb-index
>         lrwxrwxrwx 1     5 Mar 19 23:05 symlink -> a.out*
> 
> GDB generates the .gdb-index file with a name that matches the name of
> the actual program (a.out.gdb-index here), not the symlink that
> references it.  The remaining of the script is looking for a file named
> after the provided argument (would be 'symlink.gdb-index' in our
> example).
> 
> gdb/ChangeLog:
> 
> 	PR gdb/27614
> 	* contrib/gdb-add-index.sh: Fix when called with a symlink as an
> 	argument.
> 
> gdb/testsuite/ChangeLog:
> 
> 	PR gdb/27614
> 	* gdb.dwarf2/gdb-add-index-symlink.exp: New test.
> ---
>  gdb/contrib/gdb-add-index.sh                  | 28 +++++++++++
>  .../gdb.dwarf2/gdb-add-index-symlink.exp      | 47 +++++++++++++++++++
>  2 files changed, 75 insertions(+)
>  create mode 100644 gdb/testsuite/gdb.dwarf2/gdb-add-index-symlink.exp
> 
> diff --git a/gdb/contrib/gdb-add-index.sh b/gdb/contrib/gdb-add-index.sh
> index 2ac3fddbf26..734110caa3b 100755
> --- a/gdb/contrib/gdb-add-index.sh
> +++ b/gdb/contrib/gdb-add-index.sh
> @@ -37,6 +37,34 @@ fi
>  
>  file="$1"
>  
> +if test -L "$file"; then
> +    if ! command -v readlink >/dev/null 2>&1; then
> +	echo "$myname: 'readlink' missing.  Failed to follow symlink $1." 1>&2
> +	exit 1
> +    fi
> +
> +    # Count number of links followed in order to detect loops.
> +    count=0
> +    while test -L "$file"; do
> +	target=$(readlink "$file")
> +
> +	case "$target" in
> +	    /*)
> +		file="$target"
> +		;;
> +	    *)
> +		file="$(dirname "$file")/$target"
> +		;;
> +	esac
> +
> +	count="$((count + 1))"
> +	if test "$count" -gt 10; then
> +	    echo "$myname: Detected loop while following link $file"
> +	    exit 1
> +	fi
> +    done
> +fi
> +
>  if test ! -r "$file"; then
>      echo "$myname: unable to access: $file" 1>&2
>      exit 1
> diff --git a/gdb/testsuite/gdb.dwarf2/gdb-add-index-symlink.exp b/gdb/testsuite/gdb.dwarf2/gdb-add-index-symlink.exp
> new file mode 100644
> index 00000000000..eaeddec0250
> --- /dev/null
> +++ b/gdb/testsuite/gdb.dwarf2/gdb-add-index-symlink.exp
> @@ -0,0 +1,47 @@
> +# Copyright 2021 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +load_lib dwarf.exp
> +
> +# This test can only be run on targets which support DWARF-2.
> +if {![dwarf2_support]} {
> +    return 0
> +}
> +
> +standard_testfile main.c
> +
> +if { [prepare_for_testing "failed to prepare" "${testfile}" \
> +	  [list ${srcfile}]] } {
> +    return -1
> +}
> +
> +set symlink [file dirname $binfile]/symlink
> +
> +if { ![file exists $symlink] } {
> +    file link -symbolic $symlink $binfile
> +}
> +
> +if { [ensure_gdb_index $symlink] == -1 } {
> +    fail "Unable to call gdb-add-index with a symlink to a symfile"
> +    return -1
> +}
> +
> +# Ok, we have a copy of $binfile with an index.
> +# Restart gdb and verify the index was used.
> +
> +clean_restart $symlink
> +gdb_test "mt print objfiles ${testfile}" \
> +    "(gdb_index|debug_names).*" \
> +    "index used"
> -- 
> 2.30.1
> 

-- 
Lancelot SIX