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target/arm: Implement new v8.1M NOCP check for exception return

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In v8.1M a new exception return check is added which may cause a NOCP
UsageFault (see rule R_XLTP): before we clear s0..s15 and the FPSCR
we must check whether access to CP10 from the Security state of the
returning exception is disabled; if it is then we must take a fault.

(Note that for our implementation CPPWR is always RAZ/WI and so can
never cause CP10 accesses to fail.)

The other v8.1M change to this register-clearing code is that if MVE
is implemented VPR must also be cleared, so add a TODO comment to
that effect.

Backports 3423fbf10427db7680d3237d4f62d8370052fca0
This commit is contained in:
Peter Maydell 2021-03-03 18:57:50 -05:00 committed by Lioncash
parent 05d479a8c0
commit f02045f5f5
1 changed files with 21 additions and 1 deletions
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22
qemu/target/arm/m_helper.c
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@ -1438,7 +1438,27 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
v7m_exception_taken(cpu, excret, true, false);
return;
} else {
/* Clear s0..s15 and FPSCR */
if (arm_feature(env, ARM_FEATURE_V8_1M)) {
/* v8.1M adds this NOCP check */
bool nsacr_pass = exc_secure ||
extract32(env->v7m.nsacr, 10, 1);
bool cpacr_pass = v7m_cpacr_pass(env, exc_secure, true);
if (!nsacr_pass) {
//armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE, true);
env->v7m.cfsr[M_REG_S] |= R_V7M_CFSR_NOCP_MASK;
qemu_log_mask(CPU_LOG_INT, "...taking UsageFault on existing "
"stackframe: NSACR prevents clearing FPU registers\n");
v7m_exception_taken(cpu, excret, true, false);
} else if (!cpacr_pass) {
//armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE,
// exc_secure);
env->v7m.cfsr[exc_secure] |= R_V7M_CFSR_NOCP_MASK;
qemu_log_mask(CPU_LOG_INT, "...taking UsageFault on existing "
"stackframe: CPACR prevents clearing FPU registers\n");
v7m_exception_taken(cpu, excret, true, false);
}
}
/* Clear s0..s15 and FPSCR; TODO also VPR when MVE is implemented */
int i;
for (i = 0; i < 16; i += 2) {