Re: [PATCH v2 1/1] LoongArch: Add static PIE support

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 23/09/22 08:16, Xi Ruoyao via Libc-alpha wrote:
> If the compiler is new enough, enable static PIE support.  In the static
> PIE version of _start (in rcrt1.o), use la.pcrel instead of la.got
> because in a static PIE we cannot use GOT entries until the dynamic
> relocations for GOT are resolved.


The patch looks ok and with a recent GCC I see both SUPPORT_STATIC_PIE
and ENABLE_STATIC_PIE being set.

$ loongarch64-glibc-linux-gnu-gcc -v 2>&1 | tail -n1
gcc version 13.0.0 20220923 (experimental) [releases/gcc-12 r12-8552-g65941a91091] (GCC)
$ loongarch64-glibc-linux-gnu-ld -v
GNU ld (GNU Binutils) 2.39.0.20220923

However I can't actually build glibc:

make[2]: Entering directory '/home/azanella/Projects/glibc/glibc-git/support'
/home/azanella/toolchain/install/compilers//loongarch64-linux-gnu-lp64d/bin/loongarch64-glibc-linux-gnu-gcc -o /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/support/test-run-command -nostdlib -nostartfiles -static -static-pie     /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/csu/rcrt1.o /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/csu/crti.o `/home/azanella/toolchain/install/compilers//loongarch64-linux-gnu-lp64d/bin/loongarch64-glibc-linux-gnu-gcc  --print-file-name=crtbeginS.o` /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/support/test-run-command.o /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/elf/static-stubs.o /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/support/libsupport_nonshared.a -Wl,-z,now -Wl,--start-group /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/libc.a -lgcc  -Wl,--end-group `/home/azanella/toolchain/install/compilers//loongarch64-linux-gnu-lp64d/bin/loongarch64-glibc-linux-gnu-gcc  --print-file-name=crtendS.o` /home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/csu/crtn.o
/home/azanella/Projects/glibc/build/loongarch64-linux-gnu-lp64d/libc.a(setlocale.o)(__libc_freeres_fn+0x144): error: R_LARCH_SOP_PUSH_TLS_GOT against [undefweak] `_nl_current_LC_COLLATE':
Internal: Shouldn't be resolved to const.

Using --disable-default-pie avoids this build issue.


> ---
>  sysdeps/loongarch/configure    | 37 ++++++++++++++++++++++++++++++++++
>  sysdeps/loongarch/configure.ac | 20 ++++++++++++++++++
>  sysdeps/loongarch/start.S      | 14 ++++++++++---
>  3 files changed, 68 insertions(+), 3 deletions(-)
> 
> diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure
> index 43b54d4965..4c1dd303bf 100644
> --- a/sysdeps/loongarch/configure
> +++ b/sysdeps/loongarch/configure
> @@ -3,3 +3,40 @@
>  
>  $as_echo "#define HIDDEN_VAR_NEEDS_DYNAMIC_RELOC 1" >>confdefs.h
>  
> +
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if the compiler is sufficient to build static PIE on LoongArch" >&5
> +$as_echo_n "checking if the compiler is sufficient to build static PIE on LoongArch... " >&6; }
> +if ${libc_cv_static_pie_on_loongarch+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +
> +  cat > conftest.c << EOF
> +extern int x __asm__("y");
> +int y;
> +void *_start() { return &x; }
> +EOF
> +  libc_cv_static_pie_on_loongarch=no
> +  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest conftest.c'
> +  { { eval echo "\"\$as_me\":${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 $READELF -Wr conftest | grep -q R_LARCH_RELATIVE'
> +  { { eval echo "\"\$as_me\":${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; }; }
> +  then
> +    libc_cv_static_pie_on_loongarch=yes
> +  fi
> +  rm -rf conftest.*
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_static_pie_on_loongarch" >&5
> +$as_echo "$libc_cv_static_pie_on_loongarch" >&6; }
> +
> +if test "$libc_cv_static_pie_on_loongarch" = yes; then
> +  $as_echo "#define SUPPORT_STATIC_PIE 1" >>confdefs.h
> +
> +fi
> diff --git a/sysdeps/loongarch/configure.ac b/sysdeps/loongarch/configure.ac
> index f744367bf3..f389679459 100644
> --- a/sysdeps/loongarch/configure.ac
> +++ b/sysdeps/loongarch/configure.ac
> @@ -4,3 +4,23 @@ GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
>  dnl It is always possible to access static and hidden symbols in an
>  dnl position independent way.
>  AC_DEFINE(HIDDEN_VAR_NEEDS_DYNAMIC_RELOC)
> +
> +dnl test if GCC is new enough for static PIE.
> +AC_CACHE_CHECK([if the compiler is sufficient to build static PIE on LoongArch],
> +libc_cv_static_pie_on_loongarch, [
> +  cat > conftest.c << EOF
> +extern int x __asm__("y");
> +int y;
> +void *_start() { return &x; }
> +EOF
> +  libc_cv_static_pie_on_loongarch=no
> +  if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest conftest.c]) \
> +     && AC_TRY_COMMAND([LC_ALL=C $READELF -Wr conftest | grep -q R_LARCH_RELATIVE])
> +  then
> +    libc_cv_static_pie_on_loongarch=yes
> +  fi
> +  rm -rf conftest.*])
> +
> +if test "$libc_cv_static_pie_on_loongarch" = yes; then
> +  AC_DEFINE(SUPPORT_STATIC_PIE)
> +fi
> diff --git a/sysdeps/loongarch/start.S b/sysdeps/loongarch/start.S
> index e66af16d57..05cabd9b96 100644
> --- a/sysdeps/loongarch/start.S
> +++ b/sysdeps/loongarch/start.S
> @@ -60,9 +60,17 @@ ENTRY (ENTRY_POINT)
>  	cfi_undefined (1)
>  	or		a5, a0, zero /* rtld_fini */
>  
> +#if defined(PIC) && !defined(SHARED)
> +/* For static PIE, the GOT cannot be used in _start because the GOT entries are
> +   offsets instead of real addresses before __libc_start_main.  */
> +# 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.  */
> -	la.got		a0, t0, main
> +# define LA la.got
> +#endif
> +
> +	LA		a0, t0, main
>  	REG_L		a1, sp, 0
>  	ADDI		a2, sp, SZREG
>  
> @@ -73,9 +81,9 @@ ENTRY (ENTRY_POINT)
>  	move		a4, zero /* used to be fini */
>  	or		a6, sp, zero /* stack_end */
>  
> -	la.got		ra, t0, __libc_start_main
> +	LA		ra, t0, __libc_start_main
>  	jirl		ra, ra, 0
>  
> -	la.got		ra, t0, abort
> +	LA		ra, t0, abort
>  	jirl		ra, ra, 0
>  END (ENTRY_POINT)