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

[Xi Ruoyao <xry111@xry111.site>]

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, $a0, %pc_lo12(x)
+  syscall 0
+
+.data
+x:
+  .word 0
+  /* This should produce an R_LARCH_RELATIVE in the static PIE.  */
+  .dword _start
+EOF
+  libc_cv_static_pie_on_loongarch=no
+  if AC_TRY_COMMAND([${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)
-- 
2.37.0