Re: [PATCH v3 1/1] LoongArch: Add static PIE support

[caiyinyu <caiyinyu@loongson.cn>]

在 2022/9/24 下午3:45, 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    | 48 ++++++++++++++++++++++++++++++++++
>   sysdeps/loongarch/configure.ac | 36 +++++++++++++++++++++++++
>   sysdeps/loongarch/start.S      | 14 +++++++---
>   3 files changed, 95 insertions(+), 3 deletions(-)
>
> diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure
> index 43b54d4965..70d6fec5c1 100644
> --- a/sysdeps/loongarch/configure
> +++ b/sysdeps/loongarch/configure
> @@ -3,3 +3,51 @@
>   
>   $as_echo "#define HIDDEN_VAR_NEEDS_DYNAMIC_RELOC 1" >>confdefs.h
>   
> +
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if the toolchain is sufficient to build static PIE on LoongArch" >&5
> +$as_echo_n "checking if the toolchain 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.S << EOF
> +.global _start
> +.type _start, @function
> +_start:
> +  li.w $a7, 93
> +  /* This ensures the assembler supports explicit reloc.  */
> +  pcalau12i $a0, %pc_hi20(x)
> +  ld.w $a0, $a0, %pc_lo12(x)
> +  syscall 0
> +
> +.data
> +x:
> +  .word 0
> +  /* This should produce an R_LARCH_RELATIVE in the static PIE.  */
> +  .dword _start
> +EOF
> +  libc_cv_static_pie_on_loongarch=no
> +  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest conftest.S'
> +  { { eval echo "\"\$as_me\":${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 $READELF -Wr conftest | grep -q R_LARCH_RELATIVE'
> +  { { eval echo "\"\$as_me\":${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..282b95b0fb 100644
> --- a/sysdeps/loongarch/configure.ac
> +++ b/sysdeps/loongarch/configure.ac
> @@ -4,3 +4,39 @@ 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 the toolchain is new enough for static PIE.
> +dnl We need a GAS supporting explicit reloc (older GAS produces stack-based
> +dnl reloc and triggers an internal error in the linker).  And, we need GCC to
> +dnl pass the correct linker flags for static PIE.  GCC >= 13 and GAS >= 2.40
> +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
> +.global _start
> +.type _start, @function
> +_start:
> +  li.w $a7, 93
> +  /* This ensures the assembler supports explicit reloc.  */
> +  pcalau12i $a0, %pc_hi20(x)
> +  ld.w $a0, $a0, %pc_lo12(x)
> +  syscall 0
> +
> +.data
> +x:
> +  .word 0


Tested on LoongArch machine with latest gcc and binutils (master):

gcc 13 fa4bc21bac70df5ae5712a1933a2e6bb5bf8d42b

binutils 2.39 4f56cf059ca883ca86c8f15cfc8a3e27465bf4b0

linux kernel 5.19

All passed.

Here are some mistakes:

diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure
index 70d6fec5c1..6edd6d08a5 100644
--- a/sysdeps/loongarch/configure
+++ b/sysdeps/loongarch/configure
@@ -14,10 +14,10 @@ else
  .global _start
  .type _start, @function
  _start:
-  li.w $a7, 93
+  li.w \$a7, 93
    /* This ensures the assembler supports explicit reloc.  */
-  pcalau12i $a0, %pc_hi20(x)
-  ld.w $a0, $a0, %pc_lo12(x)
+  pcalau12i \$a0, %pc_hi20(x)
+  ld.w \$a0, \$a0, %pc_lo12(x)
    syscall 0

  .data
diff --git a/sysdeps/loongarch/configure.ac b/sysdeps/loongarch/configure.ac
index 282b95b0fb..a8a373bea3 100644
--- a/sysdeps/loongarch/configure.ac
+++ b/sysdeps/loongarch/configure.ac
@@ -17,10 +17,10 @@ libc_cv_static_pie_on_loongarch, [
  .global _start
  .type _start, @function
  _start:
-  li.w $a7, 93
+  li.w \$a7, 93
    /* This ensures the assembler supports explicit reloc.  */
-  pcalau12i $a0, %pc_hi20(x)
-  ld.w $a0, $a0, %pc_lo12(x)
+  pcalau12i \$a0, %pc_hi20(x)
+  ld.w \$a0, \$a0, %pc_lo12(x)
    syscall 0

  .data



> +  /* This should produce an R_LARCH_RELATIVE in the static PIE.  */
> +  .dword _start
> +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 $READELF -Wr conftest | grep -q R_LARCH_RELATIVE])
> +  then
> +    libc_cv_static_pie_on_loongarch=yes
> +  fi
> +  rm -rf conftest.*])
> +
> +if test "$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)