[gcc r11-8901] arm: testsuite: improve detection of CMSE hardware.

[Richard Earnshaw <rearnsha@gcc.gnu.org>]

https://gcc.gnu.org/g:e5b56e805835b3052f67a03c0379db0adc1300a3

commit r11-8901-ge5b56e805835b3052f67a03c0379db0adc1300a3
Author: Richard Earnshaw <rearnsha@arm.com>
Date:   Fri Jun 18 17:13:04 2021 +0100

    arm: testsuite: improve detection of CMSE hardware.
    
    The test for CMSE support being available in hardware currently
    relies on the compiler not optimizing away a secure gateway operation.
    But even that is suspect, because the SG instruction is just a NOP
    on armv8-m implementations that do not support the security extension.
    
    Replace the existing test with a new one that reads and checks
    the appropriate hardware feature register (memory mapped).  This has
    to be run from secure mode, but that shouldn't matter, because if we
    can't do that we can't really test the CMSE extensions anyway.  We
    retain the SG instruction to ensure the test can't pass accidentally
    if run on pre-armv8-m devices.
    
    gcc/testsuite:
            * lib/target-supports.exp (check_effective_target_arm_cmse_hw):
            New function.
    
    (cherry picked from commit 79fb2700bdbab4212346d907be6063c5a32d3836)

Diff:
---
 gcc/testsuite/lib/target-supports.exp | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 411e559f508..8aebd2e9a91 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -4861,6 +4861,23 @@ proc check_effective_target_arm_cmse_ok {} {
     } "-mcmse"];
 }
 
+# Return 1 if the target supports executing CMSE instructions, 0
+# otherwise.  Cache the result.
+
+proc check_effective_target_arm_cmse_hw { } {
+    return [check_runtime arm_cmse_hw_available {
+	int main (void)
+	{
+	    unsigned id_pfr1;
+	    asm ("ldr\t%0, =0xe000ed44\n" \
+		 "ldr\t%0, [%0]\n" \
+		 "sg" : "=l" (id_pfr1));
+	    /* Exit with code 0 iff security extension is available.  */
+	    return !(id_pfr1 & 0xf0);
+	}
+    } "-mcmse"]
+}
+
 # Return 1 if the target supports executing MVE instructions, 0
 # otherwise.