fix(aarch64): allow build with ARM_ARCH_MINOR=4

When building the FVP platform with SPMD (which activates the context
switch code), but keeping ARM_ARCH_MINOR to 4 or lower, the assembler
will complain about the SCXTNUM_EL2 system register not being supported
by the "selected processor".

Allow building this combination of options by defining the SCXTNUM_EL2
register via the generic S3_ encoding, so any assembler, with any -march
settings, will generate the access without any warnings.

We do protect accesses to this register by runtime checks, if not
explicitly requested otherwise, so can override the toolchain in this
case.

Change-Id: I0941f4c4dcf541bd968c153b9c3fac61ca23f7ef
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

diff --git a/include/arch/aarch64/arch.h b/include/arch/aarch64/arch.h
index 2ce1be8f053a1edc8db41a86f6b52233f8e185ba..dee7fdcff2b0df6ef0ba5e7a3a36bddc3449a3ca 100644 (file)
--- a/include/arch/aarch64/arch.h
+++ b/include/arch/aarch64/arch.h
@@ -1234,6 +1234,8 @@
 #define GPCCR_EL3                      S3_6_C2_C1_6
 #define GPTBR_EL3                      S3_6_C2_C1_4
 
+#define SCXTNUM_EL2                    S3_4_C13_C0_7
+
 /*******************************************************************************
  * RAS system registers
  ******************************************************************************/