Open Source & Linux Lab

• git tree: https://github.com/jcmvbkbc/binutils-gdb-xtensa

• [+] static linking
• [+] PDE
• [+] PIE
• [-] PLT and lazy binding
• [-] TLS

Default local call

+0:     movi    tmp, target@GOT
+3:     add     tmp, tmp, localGOTptr
+5:     l32i    tmp, tmp, 0
+7:     mov     GOTptr, localGOTptr
+9:     callx0  tmp

No-GOT local call

+0:     movi    tmp1, target
+3:     l32i    tmp2, localGOTptr, TEXT_SEGMENT_OFFSET
+5:     add     tmp1, tmp1, tmp2
+7:     mov     GOTptr, localGOTptr
+9:     callx0  tmp1

When call0 reaches the target it can be transformed to

+0:     mov     GOTptr, localGOTptr
+2:     call0   target

In the j.l style it could probably be done like

        call0.l target, tmp1, tmp2, localGOTptr

Obvious version:

+0:     movi    tmp, target@PLTGOT
+3:     add     tmp, tmp, localGOTptr
+5:     l32i    tmp, tmp, 0
+7:     l32i    GOTptr, tmp, 4
+9:     l32i    tmp, tmp, 0
+11:    callx0  tmp

target@PLT:
+0:     movi    a8, target@PLTGOT
+3:     add     a8, a8, GOTptr
+5:     movi    a9, target-symbol
+8:     l32i    a10, GOTptr, RESOLVER_FN
+10:    l32i    GOTptr, GOTptr, RESOLVER_GOT
+12:    jx0     a10

The inline part calls the PLT part only once, after resolution the inline part calls the target directly. The adjustment is done to a single GOT entry, so it's atomic. The inline part can be reduced to a fixed direct call to the PLT:

+0:     mov     GOTptr, localGOTptr
+2:     call0   target@PLT

that reduces the inline part from 14 to 5 bytes, but adds two jumps to each call and some special logic to the resolver to avoid name resolution on each call.

#! /bin/bash -ex

target=${TARGET:-xtensa-linux-uclibcfdpic}
build_base=`pwd`/build
src_base=$(dirname $(readlink -f "$0"))
binutils_src=$HOME/ws/tensilica/binutils-gdb/binutils-gdb
gcc_src=$HOME/ws/tensilica/gcc/gcc
linux_src="$src_base/linux"
uclibc_src="$src_base/uclibc-ng"
uclibc_config_src="$src_base/uclibc-ng-config"

prefix=`pwd`
sysroot="$prefix/$target/sysroot"
linux_headers="$sysroot/usr"

_FLAGS_FOR_HOST=${FLAGS_FOR_HOST:--Og -g}
_FLAGS_FOR_TARGET=${FLAGS_FOR_TARGET:--mauto-litpools -mfdpic -Oz -g}
CROSS_COMPILE=${CROSS_COMPILE:-$prefix/bin/$target-}
TARGET_CFLAGS="$_FLAGS_FOR_TARGET -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64"

if [ "$1" = "-r" ]; then
        reconfigure=1
fi

mkdir -p .build

mkdir .build/binutils && (
        cd .build/binutils
        "$binutils_src/configure" --prefix="$prefix" \
                --target=$target \
                --with-sysroot="$sysroot" \
                --disable-shared --disable-werror --disable-gdb --disable-gdbstub \
                CFLAGS="$_FLAGS_FOR_HOST"

        make -j8
        make -j8 install
)

mkdir .build/gcc-initial && (
        cd .build/gcc-initial
        "$gcc_src/configure" --prefix="$prefix" \
                --target=$target \
                --with-sysroot="$sysroot" \
                --enable-languages=c \
                --disable-shared \
                --enable-__cxa_atexit \
                --disable-tls --disable-threads \
                --without-headers --with-newlib \
                CFLAGS_FOR_TARGET="$_FLAGS_FOR_TARGET" \
                CXXFLAGS_FOR_TARGET="$_FLAGS_FOR_TARGET" \
                CFLAGS="$_FLAGS_FOR_HOST" \
                CXXFLAGS="$_FLAGS_FOR_HOST"

        make -j8 all-gcc
        make -j8 all-target-libgcc
        make -j8 install-gcc
        make -j8 install-target-libgcc
)

mkdir .build/linux && (
        cd .build/linux
        make -C "$linux_src" ARCH=xtensa \
                CROSS_COMPILE="$CROSS_COMPILE" O=`pwd` \
                defconfig   
        make -C "$linux_src" ARCH=xtensa \
                CROSS_COMPILE="$CROSS_COMPILE" O=`pwd` \
                INSTALL_HDR_PATH="$linux_headers" \
                -j8 headers_install
)

mkdir .build/uclibc && (
        cd .build/uclibc
        cp "$uclibc_config_src/.config" .
        if [ -n "$reconfigure" ]; then
                make -C "$uclibc_src" ARCH=xtensa \
                        CROSS_COMPILE="$CROSS_COMPILE" \
                        O=`pwd` KERNEL_HEADERS="$linux_headers/include" \
                        UCLIBC_EXTRA_CFLAGS="${TARGET_CFLAGS}" \
                        menuconfig
                cp .config "$uclibc_config_src"
        fi

        make -C "$uclibc_src" ARCH=xtensa \
                CROSS_COMPILE="$CROSS_COMPILE" \
                O=`pwd` KERNEL_HEADERS="$linux_headers/include" \
                UCLIBC_EXTRA_CFLAGS="${TARGET_CFLAGS}" \
                -j8 "$@"
        make -C "$uclibc_src" ARCH=xtensa \
                CROSS_COMPILE="$CROSS_COMPILE" \
                O=`pwd` KERNEL_HEADERS="$linux_headers/include" \
                UCLIBC_EXTRA_CFLAGS="${TARGET_CFLAGS}" \
                DESTDIR="$sysroot" \
                install
)

mkdir .build/gcc-final && ( 
        cd .build/gcc-final 
        "$gcc_src/configure" --prefix="$prefix" \
                --target=$target \
                --with-sysroot="$sysroot" \
                --enable-languages=c,c++ \
                --disable-shared \
                --enable-__cxa_atexit \
                --disable-tls --disable-threads \
                --with-uclibc \
                CFLAGS_FOR_TARGET="$_FLAGS_FOR_TARGET" \
                CXXFLAGS_FOR_TARGET="$_FLAGS_FOR_TARGET" \
                CFLAGS="$_FLAGS_FOR_HOST" \
                CXXFLAGS="$_FLAGS_FOR_HOST"

        make -j8 all
        make -j8 install
)