From cd6ae7ea5431c2b8f16201fb0e2c413bf8d2df06 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Fri, 16 Apr 2021 11:26:39 -0700
Subject: Set the retain attribute on _elf_set_element if CC supports [BZ
 #27492]

So that text_set_element/data_set_element/bss_set_element defined
variables will be retained by the linker.

Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
will not be optimized out; 'retain' prevents section garbage collection
if the linker support SHF_GNU_RETAIN.

GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
identifier name sections to be GCed even if there are live
__start_/__stop_ references.

Without the change, there are some static linking problems, e.g.
_IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
stdout is not flushed on exit.

Note: GCC may warning 'retain' attribute ignored while __has_attribute(retain)
is 1 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---
 configure | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

(limited to 'configure')

diff --git a/configure b/configure
index fcf43bf7de..e64b7f8efe 100755
--- a/configure
+++ b/configure
@@ -4105,6 +4105,31 @@ fi
 $as_echo "$libc_cv_textrel_ifunc" >&6; }
 
 
+# Check if CC supports attribute retain as it is used in attribute_used_retain macro.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain support" >&5
+$as_echo_n "checking for GNU attribute retain support... " >&6; }
+if ${libc_cv_gnu_retain+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.c <<EOF
+static int var  __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gnu_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
+   2>&5 ; then
+  libc_cv_gnu_retain=yes
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
+$as_echo "$libc_cv_gnu_retain" >&6; }
+if test $libc_cv_gnu_retain = yes; then
+  $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
+
+fi
+config_vars="$config_vars
+have-gnu-retain = $libc_cv_gnu_retain"
+
 # Check if gcc warns about alias for function with incompatible types.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
 $as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
@@ -5871,6 +5896,40 @@ fi
 $as_echo "$libc_linker_feature" >&6; }
 
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z start-stop-gc" >&5
+$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+  libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
+  if test -n "$libc_linker_check"; then
+    cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+				-Wl,-z,start-stop-gc -nostdlib -nostartfiles
+				-fPIC -shared -o conftest.so conftest.c
+				1>&5'
+  { { eval echo "\"\$as_me\":${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_linker_feature=yes
+    fi
+    rm -f conftest*
+  fi
+fi
+if test $libc_linker_feature = yes; then
+  libc_cv_z_start_stop_gc=yes
+else
+  libc_cv_z_start_stop_gc=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
 $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
 libc_linker_feature=no
-- 
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