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LoongArch: Fix the condition to use PC-relative addressing in start.S

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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.
This commit is contained in:
Xi Ruoyao 2022-10-02 22:23:09 +08:00 committed by caiyinyu
parent f9646d138f
commit 589eda82bb
3 changed files with 47 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
sysdeps/loongarch/configure vendored
View File

@ -10,7 +10,7 @@ if ${libc_cv_static_pie_on_loongarch+:} false; then :
$as_echo_n "(cached) " >&6
else
cat > conftest.S << EOF
cat > conftest1.S << EOF
.global _start
.type _start, @function
_start:
@ -26,14 +26,35 @@ x:
/* This should produce an R_LARCH_RELATIVE in the static PIE. */
.dword _start
EOF
cat > conftest2.S << EOF
.global f
.type f, @function
f:
/* The linker should be able to handle this and produce a PLT entry. */
la.pcrel \$t0, \$t0, external_func
jirl \$zero, \$t0, 0
EOF
libc_cv_static_pie_on_loongarch=no
if { ac_try='${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 conftest | grep -q R_LARCH_RELATIVE'
&& { 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 $READELF -Wr conftest2.so | grep -q 'R_LARCH_JUMP_SLOT.*external_func''
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
@ -42,7 +63,7 @@ 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; }

19
sysdeps/loongarch/configure.ac
View File

@ -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:
@ -29,13 +29,24 @@ 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_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)

11
sysdeps/loongarch/start.S
View File

@ -60,13 +60,16 @@ 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
/* We must get symbol main through GOT table, since main may not be local.
For instance: googletest defines main in dynamic library. */
/* 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