From dba920d34797ea8e44fca1d2cfc6a08dbe9bb759 Mon Sep 17 00:00:00 2001 From: XingLi Date: Thu, 27 Jul 2023 09:32:21 +0800 Subject: [PATCH 3/3] LoongArch: Fix the condition to use PC-relative addressing in start.S A start.o compiled from start.S with -DPIC and no -DSHARED is used by both crt1.o and rcrt1.o. So the LoongArch static PIE patch unintentionally introduced PC-relative addressing for main and __libc_start_main into crt1.o. While the latest Binutils (trunk, which will be released as 2.40) supports the PC-relative relocs against an external function by creating a PLT entry, the 2.39 release branch doesn't (and won't) support this. An error is raised: "PLT stub does not represent and symbol not defined." So, we need the following changes: 1. Check if ld supports the PC-relative relocs against an external function. If it's not supported, we deem static PIE unsupported. 2. Change start.S. If static PIE is supported, use PC-relative addressing for main and __libc_start_main and rely on the linker to create PLT entries. Otherwise, restore the old behavior (using GOT to address these functions). An alternative would be adding a new "static-pie-start.S", and some custom logic into Makefile to build rcrt1.o with it. And, restore start.S to the state before static PIE change so crt1.o won't contain PC-relative relocs against external symbols. But I can't see any benefit of this alternative, so I'd just keep it simple. Tested by building glibc with the following configurations: 1. Binutils trunk + GCC trunk. Static PIE enabled. All tests passed. 2. Binutils 2.39 branch + GCC trunk. Static PIE disabled. Tests related to ifunc failed (it's a known issue). All other tests passed. 3. Binutils 2.39 branch + GCC 12 branch, cross compilation with build-many-glibcs.py from x86_64-linux-gnu. Static PIE disabled. Build succeeded. From: Xi Ruoyao Date: Sun, 2 Oct 2022 22:23:09 +0800 --- sysdeps/loongarch/configure | 29 +++++++++++++++++++++++++---- sysdeps/loongarch/configure.ac | 18 ++++++++++++++---- sysdeps/loongarch/start.S | 9 +++++++-- 3 files changed, 46 insertions(+), 10 deletions(-) diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure index db6341e8..4f0ac252 100644 --- a/sysdeps/loongarch/configure +++ b/sysdeps/loongarch/configure @@ -11,7 +11,7 @@ if ${libc_cv_static_pie_on_loongarch+:} false; then : $as_echo_n "(cached) " >&6 else - cat > conftest.S << EOF + cat > conftest1.S << EOF .global _start .type _start, @function _start: @@ -27,14 +27,35 @@ x: /* This should produce an R_LARCH_RELATIVE in the static PIE. */ .dword _start EOF + cat > conftest2.S << EOF +.global f +.type f, @function +f: + /* The linker should be able to handle this and produce a PLT entry. */ + la.pcrel \$t0, \$t0, external_func + jirl \$zero, \$t0, 0 +EOF + libc_cv_static_pie_on_loongarch=no - if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest conftest.S' + if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest1 conftest1.S' + { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5 + (eval $ac_try) 2>&5 + ac_status=$? + $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5 + test $ac_status = 0; }; } \ + && { ac_try='LC_ALL=C $READELF -Wr conftest1 | grep -q R_LARCH_RELATIVE' + { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5 + (eval $ac_try) 2>&5 + ac_status=$? + $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5 + test $ac_status = 0; }; } \ + && { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -shared -fPIC -o conftest2.so conftest2.S' { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5 (eval $ac_try) 2>&5 ac_status=$? $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5 test $ac_status = 0; }; } \ - && { ac_try='LC_ALL=C $READELF -Wr conftest | grep -q R_LARCH_RELATIVE' + && { ac_try='LC_ALL=C $READELF -Wr conftest2.so | grep -q 'R_LARCH_JUMP_SLOT.*external_func'' { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5 (eval $ac_try) 2>&5 ac_status=$? @@ -43,7 +64,7 @@ EOF then libc_cv_static_pie_on_loongarch=yes fi - rm -rf conftest.* + rm -rf conftest* fi { $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_static_pie_on_loongarch" >&5 $as_echo "$libc_cv_static_pie_on_loongarch" >&6; } diff --git a/sysdeps/loongarch/configure.ac b/sysdeps/loongarch/configure.ac index 603085cd..bfe4e0f2 100644 --- a/sysdeps/loongarch/configure.ac +++ b/sysdeps/loongarch/configure.ac @@ -13,7 +13,7 @@ dnl satisify the requirement, but a distro may backport static PIE support into dnl earlier GCC or Binutils releases as well. AC_CACHE_CHECK([if the toolchain is sufficient to build static PIE on LoongArch], libc_cv_static_pie_on_loongarch, [ - cat > conftest.S << EOF + cat > conftest1.S << EOF .global _start .type _start, @function _start: @@ -28,14 +28,24 @@ x: .word 0 /* This should produce an R_LARCH_RELATIVE in the static PIE. */ .dword _start +EOF + cat > conftest2.S << EOF +.global f +.type f, @function +f: + /* The linker should be able to handle this and produce a PLT entry. */ + la.pcrel \$t0, \$t0, external_func + jirl \$zero, \$t0, 0 EOF libc_cv_static_pie_on_loongarch=no - if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest conftest.S]) \ - && AC_TRY_COMMAND([LC_ALL=C $READELF -Wr conftest | grep -q R_LARCH_RELATIVE]) + if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest1 conftest1.S]) \ + && AC_TRY_COMMAND([LC_ALL=C $READELF -Wr conftest1 | grep -q R_LARCH_RELATIVE]) \ + && AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -shared -fPIC -o conftest2.so conftest2.S]) \ + && AC_TRY_COMMAND([LC_ALL=C $READELF -Wr conftest2.so | grep -q 'R_LARCH_JUMP_SLOT.*external_func']) then libc_cv_static_pie_on_loongarch=yes fi - rm -rf conftest.*]) + rm -rf conftest* ]) if test "$libc_cv_static_pie_on_loongarch" = yes; then AC_DEFINE(SUPPORT_STATIC_PIE) diff --git a/sysdeps/loongarch/start.S b/sysdeps/loongarch/start.S index 1b15fc9c..87bb1d4e 100644 --- a/sysdeps/loongarch/start.S +++ b/sysdeps/loongarch/start.S @@ -44,11 +44,16 @@ ENTRY (ENTRY_POINT) cfi_undefined (1) or a5, a0, zero /* rtld_fini */ -#if defined(PIC) && !defined(SHARED) +#if ENABLE_STATIC_PIE /* For static PIE, the GOT cannot be used in _start because the GOT entries are - offsets instead of real addresses before __libc_start_main. */ + offsets instead of real addresses before __libc_start_main. + __libc_start_main and/or main may be not local, so we rely on the linker to + produce PLT entries for them. GNU ld >= 2.40 supports this. */ # define LA la.pcrel #else +/* Old GNU ld (< 2.40) cannot handle PC relative address against a non-local + function correctly. We deem these old linkers failing to support static PIE + and load the addresses from GOT. */ # define LA la.got #endif -- 2.33.0