Support multilib in sh/uClibc.

Signed-off-by: Alexey Neyman <stilor@att.net>

4 files changed, 213 insertions, 217 deletions

diff --git a/scripts/build/arch/sh.sh b/scripts/build/arch/sh.sh
index 101e4ce..6761435 100644
--- a/scripts/build/arch/sh.sh
+++ b/scripts/build/arch/sh.sh
@@ -44,9 +44,39 @@ CT_DoArchUClibcConfig() {
     CT_KconfigDisableOption "CONFIG_SH3" "${cfg}"
     CT_KconfigDisableOption "CONFIG_SH4" "${cfg}"
     CT_KconfigDisableOption "CONFIG_SH4A" "${cfg}"
-    case "${CT_ARCH_SH_VARIAN}" in
+    case "${CT_ARCH_SH_VARIANT}" in
         sh3) CT_KconfigEnableOption "CONFIG_SH3" "${cfg}";;
         sh4) CT_KconfigEnableOption "CONFIG_SH4" "${cfg}";;
         sh4a) CT_KconfigEnableOption "CONFIG_SH4A" "${cfg}";;
     esac
 }
+
+CT_DoArchUClibcCflags() {
+    local cfg="${1}"
+    local cflags="${2}"
+    local f
+
+    for f in ${cflags}; do
+        case "${f}" in
+            -m3)
+                CT_KconfigEnableOption "CONFIG_SH3" "${cfg}"
+                ;;
+            -m4)
+                CT_KconfigEnableOption "CONFIG_SH4" "${cfg}"
+                CT_KconfigEnableOption "UCLIBC_HAS_FPU" "${cfg}"
+                ;;
+            -m4-nofpu)
+                CT_KconfigEnableOption "CONFIG_SH4" "${cfg}"
+                CT_KconfigDisableOption "UCLIBC_HAS_FPU" "${cfg}"
+                ;;
+            -m4a)
+                CT_KconfigEnableOption "CONFIG_SH4A" "${cfg}"
+                CT_KconfigEnableOption "UCLIBC_HAS_FPU" "${cfg}"
+                ;;
+            -m4a-nofpu)
+                CT_KconfigEnableOption "CONFIG_SH4A" "${cfg}"
+                CT_KconfigDisableOption "UCLIBC_HAS_FPU" "${cfg}"
+                ;;
+        esac
+    done
+}
diff --git a/scripts/build/libc/glibc.sh b/scripts/build/libc/glibc.sh
index 8093e08..8027b8f 100644
--- a/scripts/build/libc/glibc.sh
+++ b/scripts/build/libc/glibc.sh
@@ -64,11 +64,6 @@ do_libc_post_cc() {
 #   libc_mode           : 'startfiles' or 'final'               : string    : (none)
 do_libc_backend() {
     local libc_mode
-    local -a multilibs
-    local multilib
-    local multi_dir multi_os_dir multi_root multi_flags multi_last
-    local root_suffix
-    local target
     local arg
 
     for arg in "$@"; do
@@ -88,94 +83,7 @@ do_libc_backend() {
     esac
 
     CT_mkdir_pushd "${CT_BUILD_DIR}/build-libc-${libc_mode}"
-
-    # If gcc is not configured for multilib, it still prints
-    # a single line for the default settings
-    multilibs=( $("${CT_TARGET}-gcc" -print-multi-lib 2>/dev/null) )
-    for multilib in "${multilibs[@]}"; do
-        # GCC makes the distinction between:
-        #   multilib (-print-multi-lib or -print-multi-directory) and
-        #   multilib-os (--print-multi-os-directory)
-        # as the gcc library and gcc sysroot library paths, respectively.
-        # For example, on x86_64:
-        #   multilib:    -m32=32      -m64=.
-        #   multilib-os: -m32=../lib  -m64=../lib64
-        # Moreover, while some multilibs can coexist in the same sysroot (e.g.
-        # on x86), some have a "sysroot suffix" to separate incompatible variants.
-        # Such sysroot suffixes combine with multilib-os directories, e.g.
-        # on sh4 with -m4a multilib, the search order in sysroot is (dropping some
-        # directories for brevity:
-        #   <sysroot>/m4a/lib/m4a/
-        #   <sysroot>/m4a/usr/lib/m4a/
-        #   <sysroot>/m4a/lib/
-        #   <sysroot>/m4a/usr/lib/
-        # The problem is that while GCC itself is aware of these subtleties, the
-        # binutils (notably, ld) it invokes under the hood are not. For example,
-        # if a shared library libfoo.so.1 requires libbar.so.1, ld will only search
-        # for libbar.so.1 in <sysroot>/m4a/usr/lib, but not in <sysroot>/m4a/usr/lib/m4a.
-        # In other words, 'gcc -lfoo -lbar' will work for both the default and -m4a
-        # cases, and 'gcc -lfoo' will work for the default, but not for -m4a. To
-        # address this, we first try to determine if the sysroot alone makes the
-        # configuration sufficiently unique. If there are no multilibs within the
-        # same suffixed sysroot, we can drop the multi_os_dir and both gcc and ld
-        # will work. If not, we'll supply both multi_root/multi_os_dir (which will
-        # likely break later, e.g. while building final GCC with C++ support). But,
-        # we've done all we can.
-        multi_flags=$( echo "${multilib#*;}" | ${sed} -r -e 's/@/ -/g;' )
-        multi_dir="${multilib%%;*}"
-        multi_os_dir=$( "${CT_TARGET}-gcc" -print-multi-os-directory ${multi_flags} )
-        multi_root=$( "${CT_TARGET}-gcc" -print-sysroot ${multi_flags} )
-        root_suffix="${multi_root#${CT_SYSROOT_DIR}}"
-        CT_DoExecLog ALL mkdir -p "sysroot${root_suffix}"
-        if [ -e "sysroot${root_suffix}/seen" ]; then
-            CT_DoExecLog ALL rm -f "sysroot${root_suffix}/unique"
-        else
-            CT_DoExecLog ALL touch "sysroot${root_suffix}/seen" "sysroot${root_suffix}/unique"
-        fi
-    done
-
-    last_multi=
-    for multilib in "${multilibs[@]}"; do
-        last_multi=$(( ${#multilibs[@]} - 1 ))
-        if [ "${multilib%%;*}" = "${multilibs[last_multi]%%;*}" ]; then
-            # This is the last multilib build or multilib is '.'
-            # (default target, not multilib)
-            multi_last=y
-        fi
-
-        multi_flags=$( echo "${multilib#*;}" | ${sed} -r -e 's/@/ -/g;' )
-        multi_dir="${multilib%%;*}"
-        multi_os_dir=$( "${CT_TARGET}-gcc" -print-multi-os-directory ${multi_flags} )
-        multi_root=$( "${CT_TARGET}-gcc" -print-sysroot ${multi_flags} )
-        root_suffix="${multi_root#${CT_SYSROOT_DIR}}"
-
-        # Avoid multi_os_dir if it's the only directory in this sysroot.
-        if [ -e "sysroot${root_suffix}/unique" ]; then
-            multi_os_dir=.
-        fi
-
-        # Adjust target tuple according to CFLAGS + any GLIBC quirks
-        target="${CT_TARGET}"
-        CT_DoMultilibTarget target ${extra_flags}
-        CT_DoArchGlibcAdjustTuple target
-        CT_DoStep INFO "Building for multilib '${multi_flags}'"
-
-        # Ensure sysroot (with suffix, if applicable) exists
-        CT_DoExecLog ALL mkdir -p "${multi_root}"
-        CT_mkdir_pushd "multilib_${multi_dir//\//_}"
-        do_libc_backend_once multi_dir="${multi_dir}"               \
-                             multi_os_dir="${multi_os_dir}"         \
-                             multi_flags="${multi_flags}"           \
-                             multi_root="${multi_root}"             \
-                             multi_last="${multi_last}"             \
-                             libc_mode="${libc_mode}"               \
-                             libc_target="${target}"
-
-        CT_Popd
-        CT_EndStep
-
-    done
-
+    CT_IterateMultilibs do_libc_backend_once multilib libc_mode="${libc_mode}"
     CT_Popd
     CT_EndStep
 }
@@ -184,26 +92,28 @@ do_libc_backend() {
 # Usage: do_libc_backend_once param=value [...]
 #   Parameter           : Definition                            : Type
 #   libc_mode           : 'startfiles' or 'final'               : string    : (empty)
-#   libc_target         : Build libc target triplet             : string    : (empty)
-#   multi_root          : Installation root, chosen for multilib: string    : (empty)
-#   multi_flags         : Extra CFLAGS to use (for multilib)    : string    : (empty)
-#   multi_dir           : Extra subdir for multilib (gcc)       : string    : (empty)
-#   multi_os_dir        : Extra subdir for multilib (os)        : string    : (empty)
-#   multi_last          : The last multilib target              : bool      : n
+#   multi_*             : as defined in CT_IterateMultilibs     : (varies)  :
 do_libc_backend_once() {
-    local multi_flags multi_dir multi_os_dir multi_root multi_last multi_root
+    local multi_flags multi_dir multi_os_dir multi_root multi_index multi_count
     local startfiles_dir
     local src_dir="${CT_SRC_DIR}/${CT_LIBC}-${CT_LIBC_VERSION}"
     local -a extra_config
     local -a extra_make_args
     local glibc_cflags
-    local libc_target="${CT_TARGET}"
     local arg opt
 
     for arg in "$@"; do
         eval "${arg// /\\ }"
     done
 
+    CT_DoStep INFO "Building for multilib ${multi_index}/${multi_count}: '${multi_flags}'"
+
+    # Ensure sysroot (with suffix, if applicable) exists
+    CT_DoExecLog ALL mkdir -p "${multi_root}"
+
+    # Adjust target tuple according GLIBC quirks
+    CT_DoArchGlibcAdjustTuple multi_target
+
     # Glibc seems to be smart enough to know about the cases that can coexist
     # in the same root and installs them into proper multilib-os directory; all
     # we need is to point to the right root. We do need to handle multilib-os
@@ -335,7 +245,7 @@ do_libc_backend_once() {
     CT_DoLog DEBUG "Extra config args passed : '${extra_config[*]}'"
     CT_DoLog DEBUG "Extra CFLAGS passed      : '${glibc_cflags}'"
     CT_DoLog DEBUG "Placing startfiles into  : '${startfiles_dir}'"
-    CT_DoLog DEBUG "Configuring with --host  : '${libc_target}'"
+    CT_DoLog DEBUG "Configuring with --host  : '${multi_target}'"
 
     # CFLAGS are only applied when compiling .c files. .S files are compiled with ASFLAGS,
     # but they are not passed by configure. Thus, pass everything in CC instead.
@@ -348,7 +258,7 @@ do_libc_backend_once() {
     "${src_dir}/configure"                                          \
         --prefix=/usr                                               \
         --build=${CT_BUILD}                                         \
-        --host=${libc_target}                                       \
+        --host=${multi_target}                                      \
         --cache-file="$(pwd)/config.cache"                          \
         --without-cvs                                               \
         --disable-profile                                           \
@@ -474,7 +384,7 @@ do_libc_backend_once() {
                               install_root="${multi_root}"    \
                               install
 
-        if [ "${CT_BUILD_MANUALS}" = "y" -a "${multi_last}" = "y" ]; then
+        if [ "${CT_BUILD_MANUALS}" = "y" -a "${multi_index}" = "${multi_count}" ]; then
             # We only need to build the manuals once. Only build them on the
             # last multilib target. If it's not multilib, it will happen on the
             # only target.
@@ -488,10 +398,12 @@ do_libc_backend_once() {
                                     ${CT_PREFIX_DIR}/share/doc
         fi
 
-        if [ "${CT_LIBC_LOCALES}" = "y" -a "${multi_last}" = "y" ]; then
+        if [ "${CT_LIBC_LOCALES}" = "y" -a "${multi_index}" = "${multi_count}" ]; then
             do_libc_locales
         fi
     fi # libc_mode = final
+
+    CT_EndStep
 }
 
 # Build up the addons list, separated with $1
diff --git a/scripts/build/libc/uClibc.sh b/scripts/build/libc/uClibc.sh
index edde815..046ba1d 100644
--- a/scripts/build/libc/uClibc.sh
+++ b/scripts/build/libc/uClibc.sh
@@ -66,10 +66,7 @@ do_libc() {
 # Common backend for 1st and 2nd passes.
 do_libc_backend() {
     local libc_mode
-    local -a multilibs
-    local multilib
-    local multi_dir multi_os_dir multi_flags
-    local ldso ldso_f ldso_d multilib_dir
+    local arg
 
     for arg in "$@"; do
         eval "${arg// /\\ }"
@@ -82,43 +79,7 @@ do_libc_backend() {
     esac
 
     CT_mkdir_pushd "${CT_BUILD_DIR}/build-libc-${libc_mode}"
-
-    # See glibc.sh for the explanation of this magic.
-    multilibs=( $("${CT_TARGET}-gcc" -print-multi-lib 2>/dev/null) )
-    for multilib in "${multilibs[@]}"; do
-        multi_flags=$( echo "${multilib#*;}" | ${sed} -r -e 's/@/ -/g;' )
-        multi_dir="${multilib%%;*}"
-        multi_os_dir=$( "${CT_TARGET}-gcc" -print-multi-os-directory ${multi_flags} )
-        multi_root=$( "${CT_TARGET}-gcc" -print-sysroot ${multi_flags} )
-        root_suffix="${multi_root#${CT_SYSROOT_DIR}}"
-        CT_DoExecLog ALL mkdir -p "sysroot${root_suffix}"
-        if [ -e "sysroot${root_suffix}/seen" ]; then
-            CT_DoExecLog ALL rm -f "sysroot${root_suffix}/unique"
-        else
-            CT_DoExecLog ALL touch "sysroot${root_suffix}/seen" "sysroot${root_suffix}/unique"
-        fi
-    done
-
-    for multilib in "${multilibs[@]}"; do
-        multi_flags=$( echo "${multilib#*;}" | ${sed} -r -e 's/@/ -/g;' )
-        multi_dir="${multilib%%;*}"
-        multi_os_dir=$( "${CT_TARGET}-gcc" -print-multi-os-directory ${multi_flags} )
-        multi_root=$( "${CT_TARGET}-gcc" -print-sysroot ${multi_flags} )
-        root_suffix="${multi_root#${CT_SYSROOT_DIR}}"
-
-        # Avoid multi_os_dir if it's the only directory in this sysroot.
-        if [ -e "sysroot${root_suffix}/unique" ]; then
-            multi_os_dir=.
-        fi
-
-        CT_DoStep INFO "Building for multilib '${multi_flags}'"
-        do_libc_backend_once multi_dir="${multi_dir}"               \
-                             multi_os_dir="${multi_os_dir}"         \
-                             multi_flags="${multi_flags}"           \
-                             multi_root="${multi_root}"             \
-                             libc_mode="${libc_mode}"
-        CT_EndStep
-    done
+    CT_IterateMultilibs do_libc_backend_once multilib libc_mode="${libc_mode}"
 
     if [ "${libc_mode}" = "final" -a "${CT_SHARED_LIBS}" = "y" ]; then
         # uClibc and GCC disagree where the dynamic linker lives. uClibc always
@@ -127,42 +88,7 @@ do_libc_backend() {
         # to the actual location, but only if that will not override the actual
         # file in /lib. Thus, need to do this after all the variants are built.
         echo "int main(void) { return 0; }" > test-ldso.c
-        for multilib in "${multilibs[@]}"; do
-            multi_flags=$( echo "${multilib#*;}" | ${sed} -r -e 's/@/ -/g;' )
-            multi_os_dir=$( "${CT_TARGET}-gcc" -print-multi-os-directory ${multi_flags} )
-            multi_root=$( "${CT_TARGET}-gcc" -print-sysroot ${multi_flags} )
-            root_suffix="${multi_root#${CT_SYSROOT_DIR}}"
-
-            # Avoid multi_os_dir if it's the only directory in this sysroot.
-            if [ -e "sysroot${root_suffix}/unique" ]; then
-                multi_os_dir=.
-            fi
-
-            multilib_dir="/lib/${multi_os_dir}"
-            CT_SanitizeVarDir multilib_dir
-
-            CT_DoExecLog ALL "${CT_TARGET}-gcc" -o test-ldso test-ldso.c ${multi_flags}
-            ldso=$( ${CT_TARGET}-readelf -Wl test-ldso | \
-                grep 'Requesting program interpreter: ' | \
-                sed -e 's,.*: ,,' -e 's,\].*,,' )
-            ldso_d="${ldso%/ld*.so.*}"
-            ldso_f="${ldso##*/}"
-            if [ -z "${ldso}" -o "${ldso_d}" = "${multilib_dir}" ]; then
-                # GCC cannot produce shared executable, or the base directory
-                # for ld.so is the same as the multi_os_directory
-                continue
-            fi
-
-            # If there is no such file in the expected ldso dir, create a symlink to
-            # multilib_dir ld.so
-            if [ ! -r "${multi_root}${ldso}" ]; then
-                # Convert ldso_d to "how many levels we need to go up" and remove
-                # leading slash.
-                ldso_d=$( echo "${ldso_d#/}" | sed 's,[^/]\+,..,g' )
-                CT_DoExecLog ALL ln -sf "${ldso_d}${multilib_dir}/${ldso_f}" \
-                    "${multi_root}${ldso}"
-            fi
-        done
+        CT_IterateMultilibs do_libc_ldso_fixup ldso_fixup
     fi
 
     CT_Popd
@@ -172,10 +98,10 @@ do_libc_backend() {
 # Common backend for 1st and 2nd passes, once per multilib.
 do_libc_backend_once() {
     local libc_mode
-    local multi_dir multi_os_dir multi_root multilib_dir startfiles_dir
+    local multi_dir multi_os_dir multi_root multi_flags multi_index multi_count
+    local multilib_dir startfiles_dir
     local jflag=${CT_LIBC_UCLIBC_PARALLEL:+${JOBSFLAGS}}
     local -a make_args
-    local build_dir
     local extra_cflags f cfg_cflags cf
     local hdr_install_subdir
 
@@ -183,11 +109,11 @@ do_libc_backend_once() {
         eval "${arg// /\\ }"
     done
 
+    CT_DoStep INFO "Building for multilib ${multi_index}/${multi_count}: '${multi_flags}'"
+
     # Simply copy files until uClibc has the ability to build out-of-tree
     CT_DoLog EXTRA "Copying sources to build dir"
-    build_dir="multilib_${multi_dir//\//_}"
-    CT_DoExecLog ALL cp -a "${CT_SRC_DIR}/${uclibc_name}-${CT_LIBC_VERSION}" "${build_dir}"
-    CT_Pushd "${build_dir}"
+    CT_DoExecLog ALL cp -aT "${CT_SRC_DIR}/${uclibc_name}-${CT_LIBC_VERSION}" .
 
     multilib_dir="lib/${multi_os_dir}"
     startfiles_dir="${multi_root}/usr/${multilib_dir}"
@@ -326,7 +252,40 @@ do_libc_backend_once() {
         CT_DoExecLog ALL mv "${multi_root}/usr/include.new" "${multi_root}/usr/include/${hdr_install_subdir}"
     fi
 
-    CT_Popd
+    CT_EndStep
+}
+
+do_libc_ldso_fixup() {
+    local multi_dir multi_os_dir multi_root multi_flags multi_index multi_count
+    local ldso ldso_f ldso_d multilib_dir
+
+    for arg in "$@"; do
+        eval "${arg// /\\ }"
+    done
+
+    CT_DoLog EXTRA "Checking dynamic linker for multilib '${multi_flags}'"
+
+    multilib_dir="/lib/${multi_os_dir}"
+    CT_SanitizeVarDir multilib_dir
+
+    CT_DoExecLog ALL "${CT_TARGET}-gcc" -o test-ldso ../test-ldso.c ${multi_flags}
+    ldso=$( ${CT_TARGET}-readelf -Wl test-ldso | \
+        grep 'Requesting program interpreter: ' | \
+        sed -e 's,.*: ,,' -e 's,\].*,,' )
+    CT_DoLog DEBUG "Detected dynamic linker for multilib '${multi_flags}': '${ldso}'"
+
+    ldso_d="${ldso%/ld*.so.*}"
+    ldso_f="${ldso##*/}"
+    # Create symlink if GCC produced an executable, dynamically linked, it was requesting
+    # a linker not in the current directory, and there is no such file in the expected
+    # ldso dir.
+    if [ -n "${ldso}" -a "${ldso_d}" != "${multilib_dir}" -a ! -r "${multi_root}${ldso}" ]; then
+        # Convert ldso_d to "how many levels we need to go up" and remove
+        # leading slash.
+        ldso_d=$( echo "${ldso_d#/}" | sed 's,[^/]\+,..,g' )
+        CT_DoExecLog ALL ln -sf "${ldso_d}${multilib_dir}/${ldso_f}" \
+            "${multi_root}${ldso}"
+    fi
 }
 
 # Initialises the .config file to sensible values
diff --git a/scripts/functions b/scripts/functions
index ef75e09..f1dfd12 100644
--- a/scripts/functions
+++ b/scripts/functions
@@ -1366,25 +1366,6 @@ CT_DoBuildTargetTuple() {
     fi
 }
 
-# This function determines the target tuple for a given set of compiler
-# flags, using either GCC's multiarch feature (if supported; if not,
-# GCC prints nothing and exits with status 0), falling back to calling
-# the architecture-specific functions.
-CT_DoMultilibTarget() {
-    local target_var="$1"; shift
-    local -a multi_flags=( "$@" )
-    local gcc_multiarch
-
-    gcc_multiarch=$( "${CT_TARGET}-gcc" -print-multiarch "${multi_flags[@]}" )
-    if [ -n "${gcc_multiarch}" ]; then
-        eval "${target_var}=${gcc_multiarch}"
-        return
-    fi
-
-    # Fall back to arch-specific guesswork
-    CT_DoArchMultilibTarget "${target_var}" "${multi_flags[@]}"
-}
-
 # This function does pause the build until the user strikes "Return"
 # Usage: CT_DoPause [optional_message]
 CT_DoPause() {
@@ -1529,9 +1510,9 @@ CT_DoLoadState(){
 # This function sets a kconfig option to a specific value in a .config file
 # Usage: CT_KconfigSetOption <option> <value> <file>
 CT_KconfigSetOption() {
-    option="$1"
-    value="$2"
-    file="$3"
+    local option="$1"
+    local value="$2"
+    local file="$3"
 
     ${grep} -E -q "^${option}=.*" "${file}" && \
         ${sed} -i -r -e "s;^${option}=.*$;${option}=${value};" "${file}" || \
@@ -1543,8 +1524,8 @@ CT_KconfigSetOption() {
 # This function enables a kconfig option to '=y' in a .config file
 # Usage: CT_KconfigEnableOption <option> <file>
 CT_KconfigEnableOption() {
-    option="$1"
-    file="$2"
+    local option="$1"
+    local file="$2"
 
     CT_KconfigSetOption "${option}" "y" "${file}"
 }
@@ -1552,8 +1533,8 @@ CT_KconfigEnableOption() {
 # This function disables a kconfig option in a .config file
 # Usage: CT_KconfigDisableOption <option> <file>
 CT_KconfigDisableOption() {
-    option="${1}"
-    file="${2}"
+    local option="${1}"
+    local file="${2}"
 
     ${grep} -E -q "^# ${option} is not set$" "${file}" || \
     ${grep} -E -q "^${option}=.*$" "${file}" && \
@@ -1565,11 +1546,125 @@ CT_KconfigDisableOption() {
 # is set or commented out.
 # Usage: CT_KconfigDeleteOption <option> <file>
 CT_KconfigDeleteOption() {
-    option="${1}"
-    file="${2}"
+    local option="${1}"
+    local file="${2}"
 
     ${grep} -E -q "^# ${option} is not set$" "${file}" && \
         ${sed} -i -r -e "/^# ${option} is not set$/d" "${file}" || \
     ${grep} -E -q "^${option}=.*$" "${file}" && \
         ${sed} -i -r -e "/^${option}=.*$/d" "${file}" || true
 }
+
+# Multilib iterator. The caller should be in a directory where the directories
+# will be created, one per multilib, and the specified command will be run in
+# each of them. The following arguments will be passed to the invoked command:
+#   multi_flags   CFLAGS for this multilib
+#   multi_dir     GCC internal library location for the multilib
+#   multi_os_dir  OS library location for the multilib
+#   multi_root    Sysroot for this multilib
+#   multi_target  Target tuple, either as reported by GCC or by our guesswork
+#   multi_count   Total number of multilibs
+#   multi_index   Index of the current multilib
+# Any additional arguments passed to this function will be forwarded to the called
+# function as well.
+# Usage: CT_IterateMultilibs <function> <prefix> <additional-args...>
+CT_IterateMultilibs() {
+    local func="${1}"
+    local prefix="${2}"
+    local -a multilibs
+    local multi_dir multi_os_dir multi_root multi_flags multi_index multi_target
+    local root_suffix
+
+    # Name used internally below
+    if [ "${prefix}" = "sysroot-check" ]; then
+        CT_Abort "Bad prefix used in CT_IterateMultilibs"
+    fi
+
+    # Drop mandatory arguments
+    shift 2
+
+    # If gcc is not configured for multilib, it still prints a single line
+    # for the default settings
+    multilibs=( $("${CT_TARGET}-gcc" -print-multi-lib 2>/dev/null) )
+    CT_DoExecLog ALL rm -rf "sysroot-check"
+    for multilib in "${multilibs[@]}"; do
+        # GCC makes the distinction between:
+        #   multilib (-print-multi-lib or -print-multi-directory) and
+        #   multilib-os (--print-multi-os-directory)
+        # as the gcc library and gcc sysroot library paths, respectively.
+        # For example, on x86_64:
+        #   multilib:    -m32=32      -m64=.
+        #   multilib-os: -m32=../lib  -m64=../lib64
+        # Moreover, while some multilibs can coexist in the same sysroot (e.g.
+        # on x86), some have a "sysroot suffix" to separate incompatible variants.
+        # Such sysroot suffixes combine with multilib-os directories, e.g.
+        # on sh4 with -m4a multilib, the search order in sysroot is (dropping some
+        # directories for brevity:
+        #   <sysroot>/m4a/lib/m4a/
+        #   <sysroot>/m4a/usr/lib/m4a/
+        #   <sysroot>/m4a/lib/
+        #   <sysroot>/m4a/usr/lib/
+        # The problem is that while GCC itself is aware of these subtleties, the
+        # binutils (notably, ld) it invokes under the hood are not. For example,
+        # if a shared library libfoo.so.1 requires libbar.so.1, ld will only search
+        # for libbar.so.1 in <sysroot>/m4a/usr/lib, but not in <sysroot>/m4a/usr/lib/m4a.
+        # In other words, 'gcc -lfoo -lbar' will work for both the default and -m4a
+        # cases, and 'gcc -lfoo' will work for the default, but not for -m4a. To
+        # address this, we first try to determine if the sysroot alone makes the
+        # configuration sufficiently unique. If there are no multilibs within the
+        # same suffixed sysroot, we can drop the multi_os_dir and both gcc and ld
+        # will work. If not, we'll supply both multi_root/multi_os_dir (which will
+        # likely break later, e.g. while building final GCC with C++ support). But,
+        # we've done all we can.
+        multi_flags=$( echo "${multilib#*;}" | ${sed} -r -e 's/@/ -/g;' )
+        multi_dir="${multilib%%;*}"
+        multi_os_dir=$( "${CT_TARGET}-gcc" -print-multi-os-directory ${multi_flags} )
+        multi_root=$( "${CT_TARGET}-gcc" -print-sysroot ${multi_flags} )
+        root_suffix="${multi_root#${CT_SYSROOT_DIR}}"
+        CT_DoExecLog ALL mkdir -p "sysroot-check${root_suffix}"
+        if [ -e "sysroot-check${root_suffix}/seen" ]; then
+            CT_DoExecLog ALL rm -f "sysroot-check${root_suffix}/unique"
+        else
+            CT_DoExecLog ALL touch "sysroot-check${root_suffix}/seen" \
+                "sysroot-check${root_suffix}/unique"
+        fi
+    done
+
+    # Now, actual iteration.
+    # This uses either GCC's multiarch feature (if supported; if not,
+    # GCC prints nothing and exits with status 0), falling back to calling
+    # the architecture-specific functions.
+    multi_index=1
+    for multilib in "${multilibs[@]}"; do
+        multi_flags=$( echo "${multilib#*;}" | ${sed} -r -e 's/@/ -/g;' )
+        multi_dir="${multilib%%;*}"
+        multi_os_dir=$( "${CT_TARGET}-gcc" -print-multi-os-directory ${multi_flags} )
+        multi_root=$( "${CT_TARGET}-gcc" -print-sysroot ${multi_flags} )
+        multi_target=$( "${CT_TARGET}-gcc" -print-multiarch ${multi_flags} )
+        root_suffix="${multi_root#${CT_SYSROOT_DIR}}"
+
+        # If GCC did not report the target tuple (i.e. this configuration is not
+        # multiarch-capable), fall back to our guesswork.
+        if [ -z "${multi_target}" ]; then
+            multi_target="${CT_TARGET}"
+            CT_DoArchMultilibTarget multi_target ${multi_flags}
+        fi
+
+        # Avoid multi_os_dir if it's the only directory in this sysroot.
+        if [ -e "sysroot-check${root_suffix}/unique" ]; then
+            multi_os_dir=.
+        fi
+
+        CT_mkdir_pushd "${prefix}_${multi_dir//\//_}"
+        $func multi_dir="${multi_dir}"       \
+              multi_os_dir="${multi_os_dir}" \
+              multi_flags="${multi_flags}"   \
+              multi_root="${multi_root}"     \
+              multi_target="${multi_target}" \
+              multi_index="${multi_index}"   \
+              multi_count="${#multilibs[@]}" \
+              "$@"
+        CT_Popd
+        multi_index=$((multi_index+1))
+    done
+}