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From dba920d34797ea8e44fca1d2cfc6a08dbe9bb759 Mon Sep 17 00:00:00 2001
From: XingLi <lixing@loongson.cn>
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 <xry111@xry111.site>
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
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