AArch64: use movz/movk instead of literal pools in start.S

eXecute-Only Memory (XOM) is a protection mechanism against some ROP
attacks. XOM sets the code as executable and unreadable, so the access
to any data, like literal pools, in the code section causes the fault
with XOM. The compiler can disable literal pools for C source files,
but not for assembly files, so I use movz/movk instead of literal pools
in start.S for XOM.

I add MOVL macro with movz/movk instructions like movl pseudo-instruction
in armasm, and use the macro instead of literal pools.

	* sysdeps/aarch64/start.S: Use MOVL instead of literal pools.
	* sysdeps/aarch64/sysdep.h (MOVL): Add MOVL macro.

1 files changed, 14 insertions, 0 deletions

diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
index a749a707ec..aba18de4d7 100644
--- a/sysdeps/aarch64/sysdep.h
+++ b/sysdeps/aarch64/sysdep.h
@@ -137,6 +137,20 @@
 	ldr	PTR_REG (T), [x##T, #:got_lo12:EXPR];	\
 	OP	PTR_REG (R), [x##T];
 
+/* Load an immediate into R.
+   Note R is a register number and not a register name.  */
+#ifdef __LP64__
+# define MOVL(R, NAME)					\
+	movz	PTR_REG (R), #:abs_g3:NAME;		\
+	movk	PTR_REG (R), #:abs_g2_nc:NAME;		\
+	movk	PTR_REG (R), #:abs_g1_nc:NAME;		\
+	movk	PTR_REG (R), #:abs_g0_nc:NAME;
+#else
+# define MOVL(R, NAME)					\
+	movz	PTR_REG (R), #:abs_g1:NAME;		\
+	movk	PTR_REG (R), #:abs_g0_nc:NAME;
+#endif
+
 /* Since C identifiers are not normally prefixed with an underscore
    on this system, the asm identifier `syscall_error' intrudes on the
    C name space.  Make sure we use an innocuous name.  */