etc:users:jcmvbkbc:binutils-xtensa
Table of Contents
binutils support for Xtensa
FDPIC support
- [+] static linking
- [+] PDE
- [+] PIE
- [±] PLT and lazy binding
- [+] TLS
FDPIC instruction sequences
Local call
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
PLT call
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.
TLS Support
TLS General Dynamic
+0: movi tmp1, x@GOTTLSDESC +3: add arg0, tmp1, localGOTptr # TLS_ARG +5: l32i tmp2, arg0, 0 # TLS_FUNCDESC +7: l32i GOTptr, tmp2, 4 # TLS_GOT +9: _l32i tmp3, tmp2, 0 # TLS_FUNC +12: callx0 tmp3 # TLS_CALL
This TLSDESC is not the same as the descriptor of the default xtensa toolchain. It contains two pointers, one to the resolver function, the other to that other descriptor containing DTPOFF and module index in the dtv.
TLS Local Dynamic
Header getting the address of the _TLS_MODULE_BASE_ is the same as in General Dynamic, or a possible one instruction less version:
+0: l32i arg0, localGOTptr, _TLS_MODULE_BASE_DESC_OFF +2: l32i tmp1, arg0, 0 +4: l32i GOTptr, tmp1, 4 +6: _l32i tmp2, tmp1, 0 +9: callx0 tmp2 ... +m: movi tmp3, x@DTPOFF +m+3: add res, tmp3, rv0 ...
_TLS_MODULE_BASE_DESC_OFF is a small fixed offset (16?) from the GOT base where an entry with R_XTENSA_TLSDESC(_TLS_MODULE_BASE_) relocation against it is placed.
TLS Initial Exec
+0: movi tmp1, x@GOTTPOFF +3: add tmp2, tmp1, localGOTptr # TLS_TPOFF_PTR +5: l32i tmp3, tmp2, 0 # TLS_TPOFF_LOAD +7: rur tmp4, THREADPTR +10: add res, tmp3, tmp4
TLS Local Exec
+0: movi tmp1, x@TPOFF +3: rur tmp2, THREADPTR +6: add res, tmp1, tmp2
Linker optimizations
General Dynamic -> Initial Exec
+0: movi tmp1, x@GOTTLSDESC movi tmp1, x@GOTTPOFF +3: add arg0, tmp1, localGOTptr # TLS_ARG add arg0, tmp1, localGOTptr +5: l32i tmp2, arg0, 0 # TLS_FUNCDESC l32i arg0, arg0, 0 +7: l32i GOTptr, tmp2, 4 # TLS_GOT nop +9: _l32i tmp3, tmp2, 0 # TLS_FUNC rur tmp3, THREADPTR +12: callx0 tmp3 # TLS_CALL add arg0, arg0, tmp3
General Dynamic -> Local Exec
+0: movi tmp1, x@GOTTLSDESC movi tmp1, x@TPOFF +3: add arg0, tmp1, localGOTptr # TLS_ARG mov arg0, tmp1 +5: l32i tmp2, arg0, 0 # TLS_FUNCDESC nop +7: l32i GOTptr, tmp2, 4 # TLS_GOT nop +9: _l32i tmp3, tmp2, 0 # TLS_FUNC rur tmp3, THREADPTR +12: callx0 tmp3 # TLS_CALL add arg0, arg0, tmp3
Initial Exec -> Local Exec
+0: movi tmp1, x@GOTTPOFF movi tmp1, x@TPOFF +3: add tmp2, tmp1, localGOTptr # TLS_TPOFF_PTR mov tmp2, tmp1 +5: l32i tmp3, tmp2, 0 # TLS_TPOFF_LOAD mov tmp3, tmp2 +7: rur tmp4, THREADPTR rur tmp4, THREADPTR +10: add res, tmp3, tmp4 add res, tmp3, tmp4
Manual toolchain building script
#! /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
)
etc/users/jcmvbkbc/binutils-xtensa.txt · Last modified: 2024/03/18 14:47 by jcmvbkbc