Compile elf/rtld.c with -fno-tree-loop-distribute-patterns.

In GCC 10, the default at -O2 is now -ftree-loop-distribute-patterns.
This optimization causes GCC to "helpfully" convert the hand-written
loop in _dl_start into a call to memset, which is not available that
early in program startup.  Similar problems in other places in GLIBC
have been addressed by explicitly building with
-fno-tree-loop-distribute-patterns, but this one may have been
overlooked previously because it only affects targets where
HAVE_BUILTIN_MEMSET is not defined.

This patch fixes a bug observed on nios2-linux-gnu target that caused
all programs to segv on startup.

1 files changed, 6 insertions, 0 deletions

diff --git a/elf/Makefile b/elf/Makefile
index 06688181e3..b05af5ce3a 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -65,6 +65,12 @@ CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables
 CFLAGS-dl-lookup.c += -fexceptions -fasynchronous-unwind-tables
 CFLAGS-dl-iterate-phdr.c += $(uses-callbacks)
 
+# On targets without __builtin_memset, rtld.c uses a hand-coded loop
+# in _dl_start.  Make sure this isn't turned into a call to regular memset.
+ifeq (yes,$(have-loop-to-function))
+CFLAGS-rtld.c += -fno-tree-loop-distribute-patterns
+endif
+
 # Compile rtld itself without stack protection.
 # Also compile all routines in the static library that are elided from
 # the shared libc because they are in libc.a in the same way.