[RFC PATCH] LoongArch: Add static PIE support

[RFC PATCH] LoongArch: Add static PIE support

[Xi Ruoyao]

Mark it as RFC because it depends on GCC [1] and Binutils [2] works.

[1]: https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601541.html
[2]: https://sourceware.org/pipermail/binutils/2022-September/122829.html

-- >8 --

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 | 14 +++++++++++++
 sysdeps/loongarch/start.S      | 14 ++++++++++---
 3 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure
index 43b54d4965..7e671241a8 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 $CC is sufficient to build static PIE on LoongArch" >&5
+$as_echo_n "checking if $CC is sufficient to build static PIE on LoongArch... " >&6; }
+if ${libc_cv_static_pie_on_loongarch+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+#if !defined __GNUC__ || __GNUC__ < 13
+#error insufficient compiler for static PIE on LoongArch
+#endif
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_cpp "$LINENO"; then :
+  libc_cv_static_pie_on_loongarch=yes
+else
+  libc_cv_static_pie_on_loongarch=no
+fi
+rm -f conftest.err conftest.i conftest.$ac_ext
+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..624897bfb3 100644
--- a/sysdeps/loongarch/configure.ac
+++ b/sysdeps/loongarch/configure.ac
@@ -4,3 +4,17 @@ 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 $CC is sufficient to build static PIE on LoongArch],
+libc_cv_static_pie_on_loongarch, [
+AC_PREPROC_IFELSE([AC_LANG_PROGRAM([[]], [[
+#if !defined __GNUC__ || __GNUC__ < 13
+#error insufficient compiler for static PIE on LoongArch
+#endif
+]])],
+	[libc_cv_static_pie_on_loongarch=yes],
+	[libc_cv_static_pie_on_loongarch=no])])
+if test "$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