add optional global visibility override
this is implemented via the build system and does not affect source
files. the idea is to use protected or hidden visibility to prevent
the compiler from pessimizing function calls within a shared (or
position-independent static) libc in the form of overhead setting up
for a call through the PLT. the ld-time symbol binding via the
-Bsymbolic-functions option already optimized out the PLT itself, but
not the code in the caller needed to support a call through the PLT.
on some archs this overhead can be substantial; on others it's
trivial.
diff --git a/configure b/configure
index 41a73b4..0e39694 100755
--- a/configure
+++ b/configure
@@ -27,6 +27,7 @@
--enable-optimize=... optimize listed components for speed over size [auto]
--enable-debug build with debugging information [disabled]
--enable-warnings build with recommended warnings flags [disabled]
+ --enable-visibility use global visibility options to optimize PIC [auto]
--enable-gcc-wrapper build musl-gcc toolchain wrapper [auto]
--disable-shared inhibit building shared library [enabled]
--disable-static inhibit building static library [enabled]
@@ -79,7 +80,7 @@
tryflag () {
printf "checking whether compiler accepts %s... " "$2"
echo "typedef int x;" > "$tmpc"
-if $CC "$2" -c -o /dev/null "$tmpc" >/dev/null 2>&1 ; then
+if $CC $2 -c -o /dev/null "$tmpc" >/dev/null 2>&1 ; then
printf "yes\n"
eval "$1=\"\${$1} \$2\""
eval "$1=\${$1# }"
@@ -124,6 +125,7 @@
optimize=auto
debug=no
warnings=no
+visibility=auto
shared=auto
static=yes
wrapper=auto
@@ -148,6 +150,8 @@
--disable-debug|--enable-debug=no) debug=no ;;
--enable-warnings|--enable-warnings=yes) warnings=yes ;;
--disable-warnings|--enable-warnings=no) warnings=no ;;
+--enable-visibility|--enable-visibility=yes) visibility=yes ;;
+--disable-visibility|--enable-visibility=no) visibility=no ;;
--enable-gcc-wrapper|--enable-gcc-wrapper=yes) wrapper=yes ;;
--disable-gcc-wrapper|--enable-gcc-wrapper=no) wrapper=no ;;
--enable-*|--disable-*|--with-*|--without-*|--*dir=*|--build=*) ;;
@@ -415,6 +419,31 @@
tryflag CFLAGS_AUTO -Wno-pointer-to-int-cast
fi
+if test "x$visibility" == xauto ; then
+# This test checks toolchain support for several things:
+# - the -include option
+# - the attributes/pragmas used in vis.h
+# - linking code that takes the address of protected symbols
+printf "checking whether global visibility preinclude works... "
+echo 'int (*fp)(void);' > "$tmpc"
+echo 'int foo(void) { }' >> "$tmpc"
+echo 'int bar(void) { fp = foo; return foo(); }' >> "$tmpc"
+if $CC $CFLAGS_C99FSE -I./arch/$ARCH -I src/internal -I./include \
+ $CPPFLAGS $CFLAGS -DSHARED -fPIC -include vis.h \
+ -nostdlib -shared -Wl,-Bsymbolic-functions \
+ -o /dev/null "$tmpc" >/dev/null 2>&1 ; then
+visibility=yes
+else
+visibility=no
+fi
+printf "%s\n" "$visibility"
+fi
+
+if test "x$visibility" == xyes ; then
+CFLAGS_AUTO="$CFLAGS_AUTO -include vis.h"
+CFLAGS_AUTO="${CFLAGS_AUTO# }"
+fi
+
# Some patched GCC builds have these defaults messed up...
tryldflag LDFLAGS_AUTO -Wl,--hash-style=both