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

[liuzhensong <liuzhensong@loongson.cn>]

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在 2022/9/23 下午7:16, Xi Ruoyao 写道:
> 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.
> ---
>   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
It takes some time to evaluate the macro of 'LA'.
> +
> +	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)