| Message ID | 20221002142309.900714-1-xry111@xry111.site |
|---|---|
| State | New |
| Headers | show |
| Series | LoongArch: Fix the condition to use PC-relative addressing in start.S | expand |
Gentle ping. I see the conclusion from review meeting is: "Should just commit these as machine maintainers." Has caiyinyu been formally promoted as a machine maintainer now? On Sun, 2022-10-02 at 22:23 +0800, Xi Ruoyao wrote: > 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. > --- > sysdeps/loongarch/configure | 29 +++++++++++++++++++++++++---- > sysdeps/loongarch/configure.ac | 19 +++++++++++++++---- > sysdeps/loongarch/start.S | 11 +++++++---- > 3 files changed, 47 insertions(+), 12 deletions(-) > > diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure > index 6edd6d08a5..3046915ce2 100644 > --- a/sysdeps/loongarch/configure > +++ b/sysdeps/loongarch/configure > @@ -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 $READELF -Wr conftest1 | grep -q > R_LARCH_RELATIVE' > + { { eval echo "\"\$as_me\":${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 $ac_try) 2>&5 > ac_status=$? > @@ -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; } > diff --git a/sysdeps/loongarch/configure.ac > b/sysdeps/loongarch/configure.ac > index a8a373bea3..06dd408ad9 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: > @@ -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) > diff --git a/sysdeps/loongarch/start.S b/sysdeps/loongarch/start.S > index 05cabd9b96..09e5a3c59c 100644 > --- a/sysdeps/loongarch/start.S > +++ b/sysdeps/loongarch/start.S > @@ -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 >
diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure index 6edd6d08a5..3046915ce2 100644 --- a/sysdeps/loongarch/configure +++ b/sysdeps/loongarch/configure @@ -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 $READELF -Wr conftest1 | grep -q R_LARCH_RELATIVE' + { { eval echo "\"\$as_me\":${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 $ac_try) 2>&5 ac_status=$? @@ -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; } diff --git a/sysdeps/loongarch/configure.ac b/sysdeps/loongarch/configure.ac index a8a373bea3..06dd408ad9 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: @@ -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) diff --git a/sysdeps/loongarch/start.S b/sysdeps/loongarch/start.S index 05cabd9b96..09e5a3c59c 100644 --- a/sysdeps/loongarch/start.S +++ b/sysdeps/loongarch/start.S @@ -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
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. --- sysdeps/loongarch/configure | 29 +++++++++++++++++++++++++---- sysdeps/loongarch/configure.ac | 19 +++++++++++++++---- sysdeps/loongarch/start.S | 11 +++++++---- 3 files changed, 47 insertions(+), 12 deletions(-)