tile: improve detection for missing -mcmodel=large support

The existing test avoided passing -mcmodel=large if the compiler didn't
support it.  However, we need to test not just the compiler support, but
also the toolchain (as and ld) support, so make the test more complete.
In addition, we have to avoid using the hwN_plt() assembly operators if
that support is missing, so guard the uses with #ifdef NO_PLT_PCREL.

This allows us to properly build glibc with the current community
binutils, which doesn't yet have the PC-relative PLT operator support.
The -mcmodel=large support is in gcc 4.8, but the toolchain support
won't be present in the community until binutils 2.24.

3 files changed, 32 insertions, 4 deletions

diff --git a/ports/sysdeps/tile/crti.S b/ports/sysdeps/tile/crti.S
index 9046010dc1..7e8e559b91 100644
--- a/ports/sysdeps/tile/crti.S
+++ b/ports/sysdeps/tile/crti.S
@@ -95,7 +95,7 @@ _init:
 	LD_PTR r0, r0
 	BEQZ r0, .Lno_weak_fn
 	jalr r0
-#elif defined(__tilegx__)
+#elif defined(__tilegx__) && !defined(NO_PLT_PCREL)
 	/* Since we are calling from the start of the object to the PLT,
 	   call by loading the full address into a register.  */
 	lnk r2
diff --git a/ports/sysdeps/tile/start.S b/ports/sysdeps/tile/start.S
index 99415647c2..3e7ec5cccf 100644
--- a/ports/sysdeps/tile/start.S
+++ b/ports/sysdeps/tile/start.S
@@ -62,6 +62,13 @@
 #include <sysdep.h>
 #include <arch/abi.h>
 
+/* Just create no-ops if we don't support PC-relative PLT relocations. */
+#ifdef NO_PLT_PCREL
+# define hw2_last_plt(x)	0
+# define hw1_plt(x)		0
+# define hw0_plt(x)		0
+#endif
+
 	.text
 	.global _start
 	.type   _start,@function
@@ -155,7 +162,11 @@ _start:
 	}
 	{
 	 ADD_PTR r4, r4, r13
-	 jalr r12
+# ifdef NO_PLT_PCREL
+	 j plt(__libc_start_main)
+# else
+	 jr r12
+# endif
 	}
 #else
 	 addli r0, r13, lo16(main - .Lmy_pc)
diff --git a/ports/sysdeps/tile/tilegx/Makefile b/ports/sysdeps/tile/tilegx/Makefile
index d3a0e970a7..4281dd98fc 100644
--- a/ports/sysdeps/tile/tilegx/Makefile
+++ b/ports/sysdeps/tile/tilegx/Makefile
@@ -1,12 +1,16 @@
 include $(common-objpfx)cflags-mcmodel-large.mk
 
+# Check for gcc to support the command-line switch, and for
+# binutils to support the hwN_plt() assembly operators and relocations.
 $(common-objpfx)cflags-mcmodel-large.mk: $(common-objpfx)config.make
 	mcmodel=no; \
-	$(CC) -S -o /dev/null -xc /dev/null -mcmodel=large && mcmodel=yes; \
+	(echo 'int main() { return getuid(); }' | \
+	 $(CC) -o /dev/null -xc - -mcmodel=large -fpic) && mcmodel=yes; \
 	echo "cflags-mcmodel-large = $$mcmodel" > $@
 
-ifeq ($(subdir),csu)
 ifeq (yes,$(cflags-mcmodel-large))
+
+ifeq ($(subdir),csu)
 # elf-init.c is in libc_nonshared.o (the end of the shared object) but
 # must reach the _init symbol at the very start of the shared object.
 CFLAGS-elf-init.c += -mcmodel=large
@@ -15,4 +19,17 @@ CFLAGS-elf-init.c += -mcmodel=large
 # with profiling, but calls to libc.so via the PLT at the very end.
 CFLAGS-gmon-start.c += -mcmodel=large
 endif
+
+else
+
+# Don't try to compile assembly code with hwN_plt() directives if the
+# toolchain doesn't support -mcmodel=large.
+ifeq ($(subdir),csu)
+CPPFLAGS-start.S += -DNO_PLT_PCREL
+CPPFLAGS-crti.S += -DNO_PLT_PCREL
+endif
+ifeq ($(subdir),nptl)
+CPPFLAGS-pt-crti.S += -DNO_PLT_PCREL
+endif
+
 endif