Re: [gentoo-portage-dev] [PATCH] estrip: rework hard link logic in save_elf_debug

[Alec Warner]

On Mon, Oct 25, 2021 at 10:10 AM Mike Gilbert <floppym@g.o> wrote:
>
> GDB loads debug files based on the file name given in the .gnu_debuglink
> section, prepended with /usr/lib/debug/${dirname}, where dirname is the
> absolute path to the parent directory of the binary being executed.
>
> For each unique inode as input, we need a link to the debug file with
> the GNU debuglink as its basename. A link to the debug file should exist
> for each directory in which the input inode exists.
>
> The debug link names should be based on the .gnu_debuglink value instead
> of the name of the file we are processing as input.
>
> The .gnu_debuglink value is based on the name of the first link
> processed for each inode. We save this value as a symlink, and then read
> it back as we process subsequent links.
>
> For example, given the following input:
>
> INODE PATH
>     1 /usr/bin/git
>     1 /usr/libexec/git-core/git-add
>     2 /usr/bin/git-shell
>     2 /usr/libexec/git-core/git-shell
>
> We generate the following inodes for the debug files:
>
> INODE DEBUGLINK
>     3 git.debug
>     4 git-shell.debug
>
> We should generate the following links:
>
> INODE PATH
>     3 /usr/lib/debug/usr/bin/git.debug
>     3 /usr/lib/debug/usr/libexec/git-core/git.debug
>     4 /usr/bin/debug/usr/bin/git-shell.debug
>     4 /usr/bin/debug/usr/libexec/git-core/git-shell.debug
>
> The previous code would have generated this broken output:
>
> INODE PATH
>     3 /usr/lib/debug/usr/bin/git.debug
>     3 /usr/lib/debug/usr/libexec/git-core/git-add.debug (*)
>     4 /usr/bin/debug/usr/bin/git-shell.debug
>     4 /usr/bin/debug/usr/libexec/git-core/git-shell.debug
>
> (*) This link has the wrong name.
>
> Bug: https://bugs.gentoo.org/820107
> Signed-off-by: Mike Gilbert <floppym@g.o>
> ---
>  bin/estrip | 31 ++++++++++++++++++++++---------
>  1 file changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/bin/estrip b/bin/estrip
> index abe523fff..8134020fd 100755
> --- a/bin/estrip
> +++ b/bin/estrip
> @@ -201,17 +201,29 @@ save_elf_debug() {
>         local x=$1
>         local inode_debug=$2
>         local splitdebug=$3
> -       local d_noslash=${D%/}
> -       local y=${ED%/}/usr/lib/debug/${x:${#d_noslash}}.debug
> +
> +       local x_basename=${x##*/}
> +       local x_dirname=${x%/*}
> +       local y_dirname=${ED%/}/usr/lib/debug/${x_dirname#${D%/}/}
> +       local y_basename y

Can we do better than X and Y here?

>
>         # dont save debug info twice
>         [[ ${x} == *".debug" ]] && return 0
>
> -       mkdir -p "${y%/*}"
> +       mkdir -p "${y_dirname}" || die
> +
> +       if [[ -L ${inode_debug} ]] ; then
> +               y_basename=$(readlink "${inode_debug}") || die
> +               y_basename=${y_basename##*/}
> +               y=${y_dirname}/${y_basename}
>
> -       if [ -f "${inode_debug}" ] ; then
> -               ln "${inode_debug}" "${y}" || die "ln failed unexpectedly"
> +               if [[ ! -e ${y} ]]; then
> +                       ln -L "${inode_debug}" "${y}" || die
> +               fi
>         else
> +               y_basename=${x_basename}.debug
> +               y=${y_dirname}/${y_basename}
> +
>                 if [[ -n ${splitdebug} ]] ; then
>                         mv "${splitdebug}" "${y}"
>                 else
> @@ -222,11 +234,12 @@ save_elf_debug() {
>                 fi
>                 # Only do the following if the debug file was
>                 # successfully created (see bug #446774).
> -               if [ $? -eq 0 ] ; then
> +               if [[ $? -eq 0 ]] ; then
>                         local args="a-x,o-w"
>                         [[ -g ${x} || -u ${x} ]] && args+=",go-r"
>                         chmod ${args} "${y}"
> -                       ln "${y}" "${inode_debug}" || die "ln failed unexpectedly"
> +                       # symlink so we can read the name back.
> +                       ln -s "${y}" "${inode_debug}" || die
>                 fi
>         fi
>
> @@ -239,8 +252,8 @@ save_elf_debug() {
>                 local buildid_dir="${ED%/}/usr/lib/debug/.build-id/${buildid:0:2}"
>                 local buildid_file="${buildid_dir}/${buildid:2}"
>                 mkdir -p "${buildid_dir}"
> -               [ -L "${buildid_file}".debug ] || ln -s "../../${x:$((${#d_noslash} + 1))}.debug" "${buildid_file}.debug"
> -               [ -L "${buildid_file}" ] || ln -s "/${x:$((${#d_noslash} + 1))}" "${buildid_file}"
> +               [[ -L "${buildid_file}".debug ]] || ln -s "../../${x#${D%/}/}.debug" "${buildid_file}.debug"
> +               [[ -L "${buildid_file}" ]] || ln -s "../../../../../${x#${D%/}/}" "${buildid_file}"
>         fi
>  }
>
> --
> 2.33.1
>
>