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.

1 files changed, 2 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index d943988d..15a30f83 100644
--- a/Makefile
+++ b/Makefile
@@ -104,6 +104,8 @@ NOSSP_SRCS = $(wildcard crt/*.c) \
 	src/ldso/dlstart.c src/ldso/dynlink.c
 $(NOSSP_SRCS:%.c=%.o) $(NOSSP_SRCS:%.c=%.lo): CFLAGS += $(CFLAGS_NOSSP)
 
+$(CRT_LIBS): CFLAGS += -DCRT
+
 # This incantation ensures that changes to any subarch asm files will
 # force the corresponding object file to be rebuilt, even if the implicit
 # rule below goes indirectly through a .sub file.