LoongArch: Fix the condition to use PC-relative addressing in start.S

A start.o compiled from start.S with -DPIC and no -DSHARED is used by
both crt1.o and rcrt1.o.  So the LoongArch static PIE patch
unintentionally introduced PC-relative addressing for main and
__libc_start_main into crt1.o.

While the latest Binutils (trunk, which will be released as 2.40)
supports the PC-relative relocs against an external function by creating
a PLT entry, the 2.39 release branch doesn't (and won't) support this.
An error is raised:

    "PLT stub does not represent and symbol not defined."

So, we need the following changes:

1. Check if ld supports the PC-relative relocs against an external
   function.  If it's not supported, we deem static PIE unsupported.
2. Change start.S.  If static PIE is supported, use PC-relative
   addressing for main and __libc_start_main and rely on the linker to
   create PLT entries.  Otherwise, restore the old behavior (using GOT
   to address these functions).

An alternative would be adding a new "static-pie-start.S", and some
custom logic into Makefile to build rcrt1.o with it.  And, restore
start.S to the state before static PIE change so crt1.o won't contain
PC-relative relocs against external symbols.  But I can't see any
benefit of this alternative, so I'd just keep it simple.

Tested by building glibc with the following configurations:

1. Binutils trunk + GCC trunk.  Static PIE enabled.  All tests
   passed.
2. Binutils 2.39 branch + GCC trunk.  Static PIE disabled.  Tests
   related to ifunc failed (it's a known issue).  All other tests
   passed.
3. Binutils 2.39 branch + GCC 12 branch, cross compilation with
   build-many-glibcs.py from x86_64-linux-gnu.  Static PIE disabled.
   Build succeeded.

1 files changed, 25 insertions, 4 deletions

diff --git a/sysdeps/loongarch/configure b/sysdeps/loongarch/configure
index 6edd6d0..3046915 100644
--- a/sysdeps/loongarch/configure
+++ b/sysdeps/loongarch/configure
@@ -10,7 +10,7 @@ if ${libc_cv_static_pie_on_loongarch+:} false; then :
   $as_echo_n "(cached) " >&6
 else
 
-  cat > conftest.S << EOF
+  cat > conftest1.S << EOF
 .global _start
 .type _start, @function
 _start:
@@ -26,14 +26,35 @@ x:
   /* This should produce an R_LARCH_RELATIVE in the static PIE.  */
   .dword _start
 EOF
+  cat > conftest2.S << EOF
+.global f
+.type f, @function
+f:
+  /* The linker should be able to handle this and produce a PLT entry.  */
+  la.pcrel \$t0, \$t0, external_func
+  jirl \$zero, \$t0, 0
+EOF
+
   libc_cv_static_pie_on_loongarch=no
-  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest conftest.S'
+  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static-pie -nostdlib -fPIE -o conftest1 conftest1.S'
+  { { eval echo "\"\$as_me\":${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 $READELF -Wr conftest1 | grep -q R_LARCH_RELATIVE'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; } \
+     && { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -shared -fPIC -o conftest2.so conftest2.S'
   { { eval echo "\"\$as_me\":${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'
+     && { ac_try='LC_ALL=C $READELF -Wr conftest2.so | grep -q 'R_LARCH_JUMP_SLOT.*external_func''
   { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
   (eval $ac_try) 2>&5
   ac_status=$?
@@ -42,7 +63,7 @@ EOF
   then
     libc_cv_static_pie_on_loongarch=yes
   fi
-  rm -rf conftest.*
+  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; }