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target/arm: Handle floating point registers in exception return
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Handle floating point registers in exception return.
This corresponds to pseudocode functions ValidateExceptionReturn(),
ExceptionReturn(), PopStack() and ConsumeExcStackFrame().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190416125744.27770-16-peter.maydell@linaro.org
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@pm215
pm215 committed Apr 29, 2019
1 parent 0dc51d6 commit 6808c4d
Showing 1 changed file with 141 additions and 1 deletion.
142 changes: 141 additions & 1 deletion target/arm/helper.c
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Expand Up @@ -8447,6 +8447,8 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
bool rettobase = false;
bool exc_secure = false;
bool return_to_secure;
bool ftype;
bool restore_s16_s31;

/* If we're not in Handler mode then jumps to magic exception-exit
* addresses don't have magic behaviour. However for the v8M
Expand Down Expand Up @@ -8484,6 +8486,16 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
excret);
}

ftype = excret & R_V7M_EXCRET_FTYPE_MASK;

if (!arm_feature(env, ARM_FEATURE_VFP) && !ftype) {
qemu_log_mask(LOG_GUEST_ERROR, "M profile: zero FTYPE in exception "
"exit PC value 0x%" PRIx32 " is UNPREDICTABLE "
"if FPU not present\n",
excret);
ftype = true;
}

if (arm_feature(env, ARM_FEATURE_M_SECURITY)) {
/* EXC_RETURN.ES validation check (R_SMFL). We must do this before
* we pick which FAULTMASK to clear.
Expand Down Expand Up @@ -8584,6 +8596,30 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
*/
write_v7m_control_spsel_for_secstate(env, return_to_sp_process, exc_secure);

/*
* Clear scratch FP values left in caller saved registers; this
* must happen before any kind of tail chaining.
*/
if ((env->v7m.fpccr[M_REG_S] & R_V7M_FPCCR_CLRONRET_MASK) &&
(env->v7m.control[M_REG_S] & R_V7M_CONTROL_FPCA_MASK)) {
if (env->v7m.fpccr[M_REG_S] & R_V7M_FPCCR_LSPACT_MASK) {
env->v7m.sfsr |= R_V7M_SFSR_LSERR_MASK;
armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_SECURE, false);
qemu_log_mask(CPU_LOG_INT, "...taking SecureFault on existing "
"stackframe: error during lazy state deactivation\n");
v7m_exception_taken(cpu, excret, true, false);
return;
} else {
/* Clear s0..s15 and FPSCR */
int i;

for (i = 0; i < 16; i += 2) {
*aa32_vfp_dreg(env, i / 2) = 0;
}
vfp_set_fpscr(env, 0);
}
}

if (sfault) {
env->v7m.sfsr |= R_V7M_SFSR_INVER_MASK;
armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_SECURE, false);
Expand Down Expand Up @@ -8745,8 +8781,105 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
}
}

if (!ftype) {
/* FP present and we need to handle it */
if (!return_to_secure &&
(env->v7m.fpccr[M_REG_S] & R_V7M_FPCCR_LSPACT_MASK)) {
armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_SECURE, false);
env->v7m.sfsr |= R_V7M_SFSR_LSERR_MASK;
qemu_log_mask(CPU_LOG_INT,
"...taking SecureFault on existing stackframe: "
"Secure LSPACT set but exception return is "
"not to secure state\n");
v7m_exception_taken(cpu, excret, true, false);
return;
}

restore_s16_s31 = return_to_secure &&
(env->v7m.fpccr[M_REG_S] & R_V7M_FPCCR_TS_MASK);

if (env->v7m.fpccr[return_to_secure] & R_V7M_FPCCR_LSPACT_MASK) {
/* State in FPU is still valid, just clear LSPACT */
env->v7m.fpccr[return_to_secure] &= ~R_V7M_FPCCR_LSPACT_MASK;
} else {
int i;
uint32_t fpscr;
bool cpacr_pass, nsacr_pass;

cpacr_pass = v7m_cpacr_pass(env, return_to_secure,
return_to_priv);
nsacr_pass = return_to_secure ||
extract32(env->v7m.nsacr, 10, 1);

if (!cpacr_pass) {
armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE,
return_to_secure);
env->v7m.cfsr[return_to_secure] |= R_V7M_CFSR_NOCP_MASK;
qemu_log_mask(CPU_LOG_INT,
"...taking UsageFault on existing "
"stackframe: CPACR.CP10 prevents unstacking "
"FP regs\n");
v7m_exception_taken(cpu, excret, true, false);
return;
} else if (!nsacr_pass) {
armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE, true);
env->v7m.cfsr[M_REG_S] |= R_V7M_CFSR_INVPC_MASK;
qemu_log_mask(CPU_LOG_INT,
"...taking Secure UsageFault on existing "
"stackframe: NSACR.CP10 prevents unstacking "
"FP regs\n");
v7m_exception_taken(cpu, excret, true, false);
return;
}

for (i = 0; i < (restore_s16_s31 ? 32 : 16); i += 2) {
uint32_t slo, shi;
uint64_t dn;
uint32_t faddr = frameptr + 0x20 + 4 * i;

if (i >= 16) {
faddr += 8; /* Skip the slot for the FPSCR */
}

pop_ok = pop_ok &&
v7m_stack_read(cpu, &slo, faddr, mmu_idx) &&
v7m_stack_read(cpu, &shi, faddr + 4, mmu_idx);

if (!pop_ok) {
break;
}

dn = (uint64_t)shi << 32 | slo;
*aa32_vfp_dreg(env, i / 2) = dn;
}
pop_ok = pop_ok &&
v7m_stack_read(cpu, &fpscr, frameptr + 0x60, mmu_idx);
if (pop_ok) {
vfp_set_fpscr(env, fpscr);
}
if (!pop_ok) {
/*
* These regs are 0 if security extension present;
* otherwise merely UNKNOWN. We zero always.
*/
for (i = 0; i < (restore_s16_s31 ? 32 : 16); i += 2) {
*aa32_vfp_dreg(env, i / 2) = 0;
}
vfp_set_fpscr(env, 0);
}
}
}
env->v7m.control[M_REG_S] = FIELD_DP32(env->v7m.control[M_REG_S],
V7M_CONTROL, FPCA, !ftype);

/* Commit to consuming the stack frame */
frameptr += 0x20;
if (!ftype) {
frameptr += 0x48;
if (restore_s16_s31) {
frameptr += 0x40;
}
}
/* Undo stack alignment (the SPREALIGN bit indicates that the original
* pre-exception SP was not 8-aligned and we added a padding word to
* align it, so we undo this by ORing in the bit that increases it
Expand All @@ -8759,7 +8892,14 @@ static void do_v7m_exception_exit(ARMCPU *cpu)
*frame_sp_p = frameptr;
}
/* This xpsr_write() will invalidate frame_sp_p as it may switch stack */
xpsr_write(env, xpsr, ~XPSR_SPREALIGN);
xpsr_write(env, xpsr, ~(XPSR_SPREALIGN | XPSR_SFPA));

if (env->v7m.secure) {
bool sfpa = xpsr & XPSR_SFPA;

env->v7m.control[M_REG_S] = FIELD_DP32(env->v7m.control[M_REG_S],
V7M_CONTROL, SFPA, sfpa);
}

/* The restored xPSR exception field will be zero if we're
* resuming in Thread mode. If that doesn't match what the
Expand Down

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