Re: [PATCH 3/4] Use POSIX nm to simplify AIX export_symbols_cmds.

[Peter Rosin]

Hi Michael,

I had a look since I wrote a patch for POSIX nm a couple of years ago
that I never submitted (I didn't see any use case) which looked very
similar, excepting the AIX-ism in your version.

On 2016-03-10 10:01, Michael Haubenwallner wrote:
> * m4/libtool.m4 (LT_PATH_NM): Detect POSIX-compatible nm for AIX.  In
> BSD mode, the AIX nm does not tell whether a symbol is weak, need to use
> POSIX mode instead.
> (_LT_CMD_GLOBAL_SYMBOLS): Support POSIX-compatible nm.  Reorder to allow
> for platform specific hooks during transformation of global_symbol_pipe
> into C source code.  For AIX, set hook to transform even weak text
> symbols as text symbols.
> (_LT_LINKER_SHLIBS): Use global_symbol_pipe to simplify forming the
> export_symbols_cmds for AIX.
> ---
>  m4/libtool.m4 | 101 
> ++++++++++++++++++++++++++++++++--------------------------
>  1 file changed, 55 insertions(+), 46 deletions(-)
> 
> diff --git a/m4/libtool.m4 b/m4/libtool.m4
> index 2c0e657..6134522 100644
> --- a/m4/libtool.m4
> +++ b/m4/libtool.m4
> @@ -3755,10 +3755,10 @@ _LT_DECL([], [want_nocaseglob], [1],
>  
>  # LT_PATH_NM
>  # ----------
> -# find the pathname to a BSD- or MS-compatible name lister
> +# find the pathname to a BSD-, POSIX- or MS-compatible name lister
>  AC_DEFUN([LT_PATH_NM],
>  [AC_REQUIRE([AC_PROG_CC])dnl
> -AC_CACHE_CHECK([for BSD- or MS-compatible name lister (nm)], lt_cv_path_NM,
> +AC_CACHE_CHECK([for BSD-, POSIX- or MS-compatible name lister (nm)], 
> lt_cv_path_NM,
>  [if test -n "$NM"; then
>    # Let the user override the test.
>    lt_cv_path_NM=$NM
> @@ -3808,6 +3808,26 @@ else
>    : ${lt_cv_path_NM=no}
>  fi])
>  if test no != "$lt_cv_path_NM"; then
> +  case $host_os in
> +  aix[[4-9]]*)
> +    # With AIX nm we need the '-l' flag to get the "weak" information
> +    # for the Import File, but '-l' is ignored with the '-B' flag.  So
> +    # we use the '-P' (POSIX) flag instead.  As users often provide the
> +    # '-B' flag, which conflicts with '-P', we drop any provided flag.
> +    # AIX nm needs the '-C' flag to disable demangling.  For both GNU
> +    # and AIX nm, the '-g' flag shows public (global) symbols only,
> +    # and the '-p' flag disables sorting to improve performance.
> +    set dummy $lt_cv_path_NM
> +    case address@hidden|@2 -V 2>&1` in
> +    *GNU* | *'with BFD'*)
> +      lt_cv_path_NM="@S|@2 -Bgp"
> +      ;;
> +    *)
> +      lt_cv_path_NM="@S|@2 -PlCgp"
> +      ;;
> +    esac
> +    ;;
> +  esac

You are overriding the user provided $NM. Not good. If a user says
NM="nm --this-will-not-work", then you will have to trust that even if
it is not likely to work. User error, so what? Adding -Bgp or -PlCgp
can only be done when the user has not specified $NM. Yes, I see that
AIX has previously added nm flags behind the back of the user, but there
is no reason to continue with that now that you are changing things.

You need to modify innards of the lt_tmp_nm loop in the else branch
a few lines up (just above the context).

>    NM=$lt_cv_path_NM
>  else
>    # Didn't find any BSD compatible name lister, look for dumpbin.
> @@ -3832,7 +3852,7 @@ fi
>  test -z "$NM" && NM=nm
>  _LT_SET_TOOL_ABI_FLAG([NM])
>  AC_SUBST([NM])
> -_LT_DECL([], [NM], [1], [A BSD- or MS-compatible name lister])dnl
> +_LT_DECL([], [NM], [1], [A BSD-, POSIX- or MS-compatible name lister])dnl
>  
>  AC_CACHE_CHECK([the name lister ($NM) interface], [lt_cv_nm_interface],
>    [lt_cv_nm_interface="BSD nm"
> @@ -3847,6 +3867,8 @@ AC_CACHE_CHECK([the name lister ($NM) interface], 
> [lt_cv_nm_interface],
>    cat conftest.out >&AS_MESSAGE_LOG_FD
>    if $GREP 'External.*some_variable' conftest.out > /dev/null; then
>      lt_cv_nm_interface="MS dumpbin"
> +  elif $GREP '^[[     ]]*_*some_variable' conftest.out > /dev/null; then
> +    lt_cv_nm_interface="POSIX nm"

Isn't this a pretty weak check, perhaps append ' B' and remove the possibility
for leading whitespace? (see my last comment below for reasoning on spaces)

>    fi
>    rm -f conftest*])
>  ])# LT_PATH_NM
> @@ -4012,8 +4034,33 @@ symcode='[[BCDEGRST]]'
>  # Regexp to match symbols that can be accessed directly from C.
>  sympat='\([[_A-Za-z]][[_A-Za-z0-9]]*\)'
>  
> +if test "$lt_cv_nm_interface" = "MS dumpbin"; then
> +  # Gets list of data symbols to import.
> +  lt_cv_sys_global_symbol_to_import="sed -n -e 's/^I .* \(.*\)$/\1/p'"
> +  # Adjust the below global symbol transforms to fixup imported variables.
> +  lt_cdecl_hook=" -e 's/^I .* \(.*\)$/extern __declspec(dllimport) char 
> \1;/p'"
> +  lt_c_name_hook=" -e 's/^I .* \(.*\)$/  {\"\1\", (void *) 0},/p'"
> +  lt_c_name_lib_hook="\
> +  -e 's/^I .* \(lib.*\)$/  {\"\1\", (void *) 0},/p'\
> +  -e 's/^I .* \(.*\)$/  {\"lib\1\", (void *) 0},/p'"
> +else
> +  # Disable hooks by default.
> +  lt_cv_sys_global_symbol_to_import=
> +  lt_cdecl_hook=
> +  lt_c_name_hook=
> +  lt_c_name_lib_hook=
> +fi
> +
>  # Define system-specific variables.
>  case $host_os in
> +aix[[4-9]]*)
> +  case `$NM -V 2>&1` in
> +  *GNU* | *'with BFD'*) ;;
> +  *)
> +    symcode='[[BDLTVWZ]]'
> +    lt_cdecl_hook=" -e 's/^W/T/p'" # weak text symbol
> +  esac
> +  ;;

Why does AIX need to export weak symbols, when W symbols are not
handled in the nm output on other systems? This seems inconsistent?

>  aix*)
>    symcode='[[BCDT]]'
>    ;;
> @@ -4054,23 +4101,6 @@ case `$NM -V 2>&1` in
>    symcode='[[ABCDGIRSTW]]' ;;
>  esac
>  
> -if test "$lt_cv_nm_interface" = "MS dumpbin"; then
> -  # Gets list of data symbols to import.
> -  lt_cv_sys_global_symbol_to_import="sed -n -e 's/^I .* \(.*\)$/\1/p'"
> -  # Adjust the below global symbol transforms to fixup imported variables.
> -  lt_cdecl_hook=" -e 's/^I .* \(.*\)$/extern __declspec(dllimport) char 
> \1;/p'"
> -  lt_c_name_hook=" -e 's/^I .* \(.*\)$/  {\"\1\", (void *) 0},/p'"
> -  lt_c_name_lib_hook="\
> -  -e 's/^I .* \(lib.*\)$/  {\"\1\", (void *) 0},/p'\
> -  -e 's/^I .* \(.*\)$/  {\"lib\1\", (void *) 0},/p'"
> -else
> -  # Disable hooks by default.
> -  lt_cv_sys_global_symbol_to_import=
> -  lt_cdecl_hook=
> -  lt_c_name_hook=
> -  lt_c_name_lib_hook=
> -fi
> -
>  # Transform an extracted symbol line into a proper C declaration.
>  # Some systems (esp. on ia64) link data and code symbols differently,
>  # so use this general approach.
> @@ -4128,6 +4158,9 @@ for ac_symprfx in "" "_"; do
>  "     s[1]~/address@hidden/{print f,s[1],s[1]; next};"\
>  "     s[1]~prfx {split(s[1],t,\"@\"); print 
> f,t[1],substr(t[1],length(prfx))}"\
>  "     ' prfx=^$ac_symprfx]"
> +  elif test "$lt_cv_nm_interface" = "POSIX nm"; then
> +    symxfrm="\\2 $ac_symprfx\\1 \\1"
> +    lt_cv_sys_global_symbol_pipe="sed -n -e 's/^[[    
> ]]*$ac_symprfx$sympat[[         ]][[    ]]*\($symcode$symcode*\)[[      ]][[  
>   ]]*.*$opt_cr$/$symxfrm/p'"

Do you really need to handle leading and multiple whitespace here?
Posix, at least as seen here
  http://pubs.opengroup.org/onlinepubs/009696699/utilities/nm.html
seems quite clear on no leading space and one space only as separator.

>    else
>      lt_cv_sys_global_symbol_pipe="sed -n -e 's/^.*[[  
> ]]\($symcode$symcode*\)[[       ]][[    
> ]]*$ac_symprfx$sympat$opt_cr$/$symxfrm/p'"
>    fi
> @@ -5009,19 +5042,7 @@ m4_if([$1], [CXX], [
>    _LT_TAGVAR(exclude_expsyms, $1)=['_GLOBAL_OFFSET_TABLE_|_GLOBAL__F[ID]_.*']
>    case $host_os in
>    aix[[4-9]]*)
> -    # If we're using GNU nm, then we don't want the "-C" option.
> -    # -C means demangle to GNU nm, but means don't demangle to AIX nm.
> -    # Without the "-l" option, or with the "-B" option, AIX nm treats
> -    # weak defined symbols like other global defined symbols, whereas
> -    # GNU nm marks them as "W".
> -    # While the 'weak' keyword is ignored in the Export File, we need
> -    # it in the Import File for the 'aix-soname' feature, so we have
> -    # to replace the "-B" option with "-P" for AIX nm.
> -    if $NM -V 2>&1 | $GREP 'GNU' > /dev/null; then
> -      _LT_TAGVAR(export_symbols_cmds, $1)='$NM -Bpg $libobjs $convenience | 
> awk '\''{ if (((\$ 2 == "T") || (\$ 2 == "D") || (\$ 2 == "B") || (\$ 2 == 
> "W")) && ([substr](\$ 3,1,1) != ".")) { if (\$ 2 == "W") { print \$ 3 " weak" 
> } else { print \$ 3 } } }'\'' | sort -u > $export_symbols'
> -    else
> -      _LT_TAGVAR(export_symbols_cmds, $1)='`func_echo_all $NM | $SED -e 
> '\''s/B\([[^B]]*\)$/P\1/'\''` -PCpgl $libobjs $convenience | awk '\''{ if 
> (((\$ 2 == "T") || (\$ 2 == "D") || (\$ 2 == "B") || (\$ 2 == "L") || (\$ 2 
> == "W") || (\$ 2 == "V") || (\$ 2 == "Z")) && ([substr](\$ 1,1,1) != ".")) { 
> if ((\$ 2 == "W") || (\$ 2 == "V") || (\$ 2 == "Z")) { print \$ 1 " weak" } 
> else { print \$ 1 } } }'\'' | sort -u > $export_symbols'
> -    fi
> +    _LT_TAGVAR(export_symbols_cmds, $1)='$NM $libobjs $convenience | 
> $global_symbol_pipe | $EGREP -v " ($exclude_expsyms)$" | awk '\''{ kw = "" } 
> /^[[VWZ]] / { kw = " weak" } { print $ 3 kw }'\'' | sort -u > $export_symbols'
>      ;;
>    pw32*)
>      _LT_TAGVAR(export_symbols_cmds, $1)=$ltdll_cmds
> @@ -5464,19 +5485,7 @@ _LT_EOF
>       exp_sym_flag='-Bexport'
>       no_entry_flag=
>        else
> -     # If we're using GNU nm, then we don't want the "-C" option.
> -     # -C means demangle to GNU nm, but means don't demangle to AIX nm.
> -     # Without the "-l" option, or with the "-B" option, AIX nm treats
> -     # weak defined symbols like other global defined symbols, whereas
> -     # GNU nm marks them as "W".
> -     # While the 'weak' keyword is ignored in the Export File, we need
> -     # it in the Import File for the 'aix-soname' feature, so we have
> -     # to replace the "-B" option with "-P" for AIX nm.
> -     if $NM -V 2>&1 | $GREP 'GNU' > /dev/null; then
> -       _LT_TAGVAR(export_symbols_cmds, $1)='$NM -Bpg $libobjs $convenience | 
> awk '\''{ if (((\$ 2 == "T") || (\$ 2 == "D") || (\$ 2 == "B") || (\$ 2 == 
> "W")) && ([substr](\$ 3,1,1) != ".")) { if (\$ 2 == "W") { print \$ 3 " weak" 
> } else { print \$ 3 } } }'\'' | sort -u > $export_symbols'
> -     else
> -       _LT_TAGVAR(export_symbols_cmds, $1)='`func_echo_all $NM | $SED -e 
> '\''s/B\([[^B]]*\)$/P\1/'\''` -PCpgl $libobjs $convenience | awk '\''{ if 
> (((\$ 2 == "T") || (\$ 2 == "D") || (\$ 2 == "B") || (\$ 2 == "L") || (\$ 2 
> == "W") || (\$ 2 == "V") || (\$ 2 == "Z")) && ([substr](\$ 1,1,1) != ".")) { 
> if ((\$ 2 == "W") || (\$ 2 == "V") || (\$ 2 == "Z")) { print \$ 1 " weak" } 
> else { print \$ 1 } } }'\'' | sort -u > $export_symbols'
> -     fi
> +     _LT_TAGVAR(export_symbols_cmds, $1)='$NM $libobjs $convenience | 
> $global_symbol_pipe | $EGREP -v " ($exclude_expsyms)$" | awk '\''{ kw = "" } 
> /^[[VWZ]] / { kw = " weak" } { print $ 3 kw }'\'' | sort -u > $export_symbols'
>       aix_use_runtimelinking=no
>  
>       # Test if we are trying to use run time linking or normal
> 

Cheers,
Peter