[PATCH v4 00/10] target/arm: Fix insn exception priorities

[PATCH v4 00/10] target/arm: Fix insn exception priorities

[Richard Henderson]

Raise pc alignment faults.
Fix single-step and pc-align priority over breakpoints.
Not yet fixing insn abort priority over breakpoints.


r~


Changes for v4:
  * Rebase on master.
  * Split some cleanups into new patches.
  * No special cases in helper_exception_pc_alignment.

Changes for v3:
  * Rebase on siginfo_t patch set -- while probably only
    force_sig_fault is required, I suspect minor conflicts
    with the other cleanups.
  * Typo fix.

Changes for v2:
  * Handle the exceptions in cpu_loop.
  * Fix how the instruction is raised for aa32 el1.
  * Add pc alignment test cases.

Richard Henderson (10):
  target/arm: Hoist pc_next to a local variable in
    aarch64_tr_translate_insn
  target/arm: Hoist pc_next to a local variable in arm_tr_translate_insn
  target/arm: Hoist pc_next to a local variable in
    thumb_tr_translate_insn
  target/arm: Split arm_pre_translate_insn
  target/arm: Advance pc for arch single-step exception
  target/arm: Split compute_fsr_fsc out of arm_deliver_fault
  target/arm: Take an exception if PC is misaligned
  target/arm: Assert thumb pc is aligned
  target/arm: Suppress bp for exceptions with more priority
  tests/tcg: Add arm and aarch64 pc alignment tests

 target/arm/helper.h               |  1 +
 target/arm/syndrome.h             |  5 +++
 linux-user/aarch64/cpu_loop.c     | 46 ++++++++++++----------
 target/arm/debug_helper.c         | 23 +++++++++++
 target/arm/gdbstub.c              |  9 ++++-
 target/arm/machine.c              | 10 +++++
 target/arm/tlb_helper.c           | 63 ++++++++++++++++++++++---------
 target/arm/translate-a64.c        | 23 +++++++++--
 target/arm/translate.c            | 58 ++++++++++++++++++++--------
 tests/tcg/aarch64/pcalign-a64.c   | 37 ++++++++++++++++++
 tests/tcg/arm/pcalign-a32.c       | 46 ++++++++++++++++++++++
 tests/tcg/aarch64/Makefile.target |  4 +-
 tests/tcg/arm/Makefile.target     |  4 ++
 13 files changed, 271 insertions(+), 58 deletions(-)
 create mode 100644 tests/tcg/aarch64/pcalign-a64.c
 create mode 100644 tests/tcg/arm/pcalign-a32.c

-- 
2.25.1

[PATCH v4 01/10] target/arm: Hoist pc_next to a local variable in aarch64_tr_translate_insn

[Richard Henderson]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/translate-a64.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index cec672f229..9c4258ccac 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -14750,6 +14750,7 @@ static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
 {
     DisasContext *s = container_of(dcbase, DisasContext, base);
     CPUARMState *env = cpu->env_ptr;
+    uint64_t pc = s->base.pc_next;
     uint32_t insn;
 
     if (s->ss_active && !s->pstate_ss) {
@@ -14769,10 +14770,10 @@ static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
         return;
     }
 
-    s->pc_curr = s->base.pc_next;
-    insn = arm_ldl_code(env, &s->base, s->base.pc_next, s->sctlr_b);
+    s->pc_curr = pc;
+    insn = arm_ldl_code(env, &s->base, pc, s->sctlr_b);
     s->insn = insn;
-    s->base.pc_next += 4;
+    s->base.pc_next = pc + 4;
 
     s->fp_access_checked = false;
     s->sve_access_checked = false;
-- 
2.25.1

[PATCH v4 02/10] target/arm: Hoist pc_next to a local variable in arm_tr_translate_insn

[Richard Henderson]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/translate.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/target/arm/translate.c b/target/arm/translate.c
index d6af5b1b03..ead77e9006 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9559,17 +9559,18 @@ static void arm_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
 {
     DisasContext *dc = container_of(dcbase, DisasContext, base);
     CPUARMState *env = cpu->env_ptr;
+    uint32_t pc = dc->base.pc_next;
     unsigned int insn;
 
     if (arm_pre_translate_insn(dc)) {
-        dc->base.pc_next += 4;
+        dc->base.pc_next = pc + 4;
         return;
     }
 
-    dc->pc_curr = dc->base.pc_next;
-    insn = arm_ldl_code(env, &dc->base, dc->base.pc_next, dc->sctlr_b);
+    dc->pc_curr = pc;
+    insn = arm_ldl_code(env, &dc->base, pc, dc->sctlr_b);
     dc->insn = insn;
-    dc->base.pc_next += 4;
+    dc->base.pc_next = pc + 4;
     disas_arm_insn(dc, insn);
 
     arm_post_translate_insn(dc);
-- 
2.25.1

[PATCH v4 03/10] target/arm: Hoist pc_next to a local variable in thumb_tr_translate_insn

[Richard Henderson]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/translate.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/target/arm/translate.c b/target/arm/translate.c
index ead77e9006..a39456ea98 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9629,25 +9629,25 @@ static void thumb_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
 {
     DisasContext *dc = container_of(dcbase, DisasContext, base);
     CPUARMState *env = cpu->env_ptr;
+    uint32_t pc = dc->base.pc_next;
     uint32_t insn;
     bool is_16bit;
 
     if (arm_pre_translate_insn(dc)) {
-        dc->base.pc_next += 2;
+        dc->base.pc_next = pc + 2;
         return;
     }
 
-    dc->pc_curr = dc->base.pc_next;
-    insn = arm_lduw_code(env, &dc->base, dc->base.pc_next, dc->sctlr_b);
+    dc->pc_curr = pc;
+    insn = arm_lduw_code(env, &dc->base, pc, dc->sctlr_b);
     is_16bit = thumb_insn_is_16bit(dc, dc->base.pc_next, insn);
-    dc->base.pc_next += 2;
+    pc += 2;
     if (!is_16bit) {
-        uint32_t insn2 = arm_lduw_code(env, &dc->base, dc->base.pc_next,
-                                       dc->sctlr_b);
-
+        uint32_t insn2 = arm_lduw_code(env, &dc->base, pc, dc->sctlr_b);
         insn = insn << 16 | insn2;
-        dc->base.pc_next += 2;
+        pc += 2;
     }
+    dc->base.pc_next = pc;
     dc->insn = insn;
 
     if (dc->pstate_il) {
-- 
2.25.1

[PATCH v4 04/10] target/arm: Split arm_pre_translate_insn

[Richard Henderson]

Create arm_check_ss_active and arm_check_kernelpage.

Reverse the order of the tests.  While it doesn't matter in practice,
because only user-only has a kernel page and user-only never sets
ss_active, ss_active has priority over execution exceptions and it
is best to keep them in the proper order.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/translate.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/target/arm/translate.c b/target/arm/translate.c
index a39456ea98..82d4e24c27 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9513,7 +9513,7 @@ static void arm_tr_insn_start(DisasContextBase *dcbase, CPUState *cpu)
     dc->insn_start = tcg_last_op();
 }
 
-static bool arm_pre_translate_insn(DisasContext *dc)
+static bool arm_check_kernelpage(DisasContext *dc)
 {
 #ifdef CONFIG_USER_ONLY
     /* Intercept jump to the magic kernel page.  */
@@ -9525,7 +9525,11 @@ static bool arm_pre_translate_insn(DisasContext *dc)
         return true;
     }
 #endif
+    return false;
+}
 
+static bool arm_check_ss_active(DisasContext *dc)
+{
     if (dc->ss_active && !dc->pstate_ss) {
         /* Singlestep state is Active-pending.
          * If we're in this state at the start of a TB then either
@@ -9562,7 +9566,7 @@ static void arm_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
     uint32_t pc = dc->base.pc_next;
     unsigned int insn;
 
-    if (arm_pre_translate_insn(dc)) {
+    if (arm_check_ss_active(dc) || arm_check_kernelpage(dc)) {
         dc->base.pc_next = pc + 4;
         return;
     }
@@ -9633,7 +9637,7 @@ static void thumb_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
     uint32_t insn;
     bool is_16bit;
 
-    if (arm_pre_translate_insn(dc)) {
+    if (arm_check_ss_active(dc) || arm_check_kernelpage(dc)) {
         dc->base.pc_next = pc + 2;
         return;
     }
-- 
2.25.1

[PATCH v4 05/10] target/arm: Advance pc for arch single-step exception

[Richard Henderson]

The size of the code covered by a TranslationBlock cannot be 0;
this is checked via assert in tb_gen_code.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/translate-a64.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 9c4258ccac..2986fe1393 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -14767,6 +14767,7 @@ static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
         assert(s->base.num_insns == 1);
         gen_swstep_exception(s, 0, 0);
         s->base.is_jmp = DISAS_NORETURN;
+        s->base.pc_next = pc + 4;
         return;
     }
 
-- 
2.25.1

[PATCH v4 06/10] target/arm: Split compute_fsr_fsc out of arm_deliver_fault

[Richard Henderson]

We will reuse this section of arm_deliver_fault for
raising pc alignment faults.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/tlb_helper.c | 45 +++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 17 deletions(-)

diff --git a/target/arm/tlb_helper.c b/target/arm/tlb_helper.c
index 12a934e924..4cacb9658f 100644
--- a/target/arm/tlb_helper.c
+++ b/target/arm/tlb_helper.c
@@ -49,25 +49,11 @@ static inline uint32_t merge_syn_data_abort(uint32_t template_syn,
     return syn;
 }
 
-static void QEMU_NORETURN arm_deliver_fault(ARMCPU *cpu, vaddr addr,
-                                            MMUAccessType access_type,
-                                            int mmu_idx, ARMMMUFaultInfo *fi)
+static uint32_t compute_fsr_fsc(CPUARMState *env, ARMMMUFaultInfo *fi,
+                                int target_el, int mmu_idx, uint32_t *ret_fsc)
 {
-    CPUARMState *env = &cpu->env;
-    int target_el;
-    bool same_el;
-    uint32_t syn, exc, fsr, fsc;
     ARMMMUIdx arm_mmu_idx = core_to_arm_mmu_idx(env, mmu_idx);
-
-    target_el = exception_target_el(env);
-    if (fi->stage2) {
-        target_el = 2;
-        env->cp15.hpfar_el2 = extract64(fi->s2addr, 12, 47) << 4;
-        if (arm_is_secure_below_el3(env) && fi->s1ns) {
-            env->cp15.hpfar_el2 |= HPFAR_NS;
-        }
-    }
-    same_el = (arm_current_el(env) == target_el);
+    uint32_t fsr, fsc;
 
     if (target_el == 2 || arm_el_is_aa64(env, target_el) ||
         arm_s1_regime_using_lpae_format(env, arm_mmu_idx)) {
@@ -88,6 +74,31 @@ static void QEMU_NORETURN arm_deliver_fault(ARMCPU *cpu, vaddr addr,
         fsc = 0x3f;
     }
 
+    *ret_fsc = fsc;
+    return fsr;
+}
+
+static void QEMU_NORETURN arm_deliver_fault(ARMCPU *cpu, vaddr addr,
+                                            MMUAccessType access_type,
+                                            int mmu_idx, ARMMMUFaultInfo *fi)
+{
+    CPUARMState *env = &cpu->env;
+    int target_el;
+    bool same_el;
+    uint32_t syn, exc, fsr, fsc;
+
+    target_el = exception_target_el(env);
+    if (fi->stage2) {
+        target_el = 2;
+        env->cp15.hpfar_el2 = extract64(fi->s2addr, 12, 47) << 4;
+        if (arm_is_secure_below_el3(env) && fi->s1ns) {
+            env->cp15.hpfar_el2 |= HPFAR_NS;
+        }
+    }
+    same_el = (arm_current_el(env) == target_el);
+
+    fsr = compute_fsr_fsc(env, fi, target_el, mmu_idx, &fsc);
+
     if (access_type == MMU_INST_FETCH) {
         syn = syn_insn_abort(same_el, fi->ea, fi->s1ptw, fsc);
         exc = EXCP_PREFETCH_ABORT;
-- 
2.25.1

[PATCH v4 07/10] target/arm: Take an exception if PC is misaligned

[Richard Henderson]

For A64, any input to an indirect branch can cause this.

For A32, many indirect branch paths force the branch to be aligned,
but BXWritePC does not.  This includes the BX instruction but also
other interworking changes to PC.  Prior to v8, this case is UNDEFINED.
With v8, this is CONSTRAINED UNPREDICTABLE and may either raise an
exception or force align the PC.

We choose to raise an exception because we have the infrastructure,
it makes the generated code for gen_bx simpler, and it has the
possibility of catching more guest bugs.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/helper.h           |  1 +
 target/arm/syndrome.h         |  5 ++++
 linux-user/aarch64/cpu_loop.c | 46 ++++++++++++++++++++---------------
 target/arm/tlb_helper.c       | 18 ++++++++++++++
 target/arm/translate-a64.c    | 15 ++++++++++++
 target/arm/translate.c        | 22 ++++++++++++++++-
 6 files changed, 87 insertions(+), 20 deletions(-)

diff --git a/target/arm/helper.h b/target/arm/helper.h
index 448a86edfd..b463d9343b 100644
--- a/target/arm/helper.h
+++ b/target/arm/helper.h
@@ -47,6 +47,7 @@ DEF_HELPER_FLAGS_3(sel_flags, TCG_CALL_NO_RWG_SE,
 DEF_HELPER_2(exception_internal, void, env, i32)
 DEF_HELPER_4(exception_with_syndrome, void, env, i32, i32, i32)
 DEF_HELPER_2(exception_bkpt_insn, void, env, i32)
+DEF_HELPER_2(exception_pc_alignment, noreturn, env, tl)
 DEF_HELPER_1(setend, void, env)
 DEF_HELPER_2(wfi, void, env, i32)
 DEF_HELPER_1(wfe, void, env)
diff --git a/target/arm/syndrome.h b/target/arm/syndrome.h
index f30f4130a2..8cde8e7243 100644
--- a/target/arm/syndrome.h
+++ b/target/arm/syndrome.h
@@ -282,4 +282,9 @@ static inline uint32_t syn_illegalstate(void)
     return (EC_ILLEGALSTATE << ARM_EL_EC_SHIFT) | ARM_EL_IL;
 }
 
+static inline uint32_t syn_pcalignment(void)
+{
+    return (EC_PCALIGNMENT << ARM_EL_EC_SHIFT) | ARM_EL_IL;
+}
+
 #endif /* TARGET_ARM_SYNDROME_H */
diff --git a/linux-user/aarch64/cpu_loop.c b/linux-user/aarch64/cpu_loop.c
index 97e0728b67..f9f3473288 100644
--- a/linux-user/aarch64/cpu_loop.c
+++ b/linux-user/aarch64/cpu_loop.c
@@ -113,27 +113,35 @@ void cpu_loop(CPUARMState *env)
             break;
         case EXCP_PREFETCH_ABORT:
         case EXCP_DATA_ABORT:
-            /* We should only arrive here with EC in {DATAABORT, INSNABORT}. */
             ec = syn_get_ec(env->exception.syndrome);
-            assert(ec == EC_DATAABORT || ec == EC_INSNABORT);
-
-            /* Both EC have the same format for FSC, or close enough. */
-            fsc = extract32(env->exception.syndrome, 0, 6);
-            switch (fsc) {
-            case 0x04 ... 0x07: /* Translation fault, level {0-3} */
-                si_signo = TARGET_SIGSEGV;
-                si_code = TARGET_SEGV_MAPERR;
+            switch (ec) {
+            case EC_DATAABORT:
+            case EC_INSNABORT:
+                /* Both EC have the same format for FSC, or close enough. */
+                fsc = extract32(env->exception.syndrome, 0, 6);
+                switch (fsc) {
+                case 0x04 ... 0x07: /* Translation fault, level {0-3} */
+                    si_signo = TARGET_SIGSEGV;
+                    si_code = TARGET_SEGV_MAPERR;
+                    break;
+                case 0x09 ... 0x0b: /* Access flag fault, level {1-3} */
+                case 0x0d ... 0x0f: /* Permission fault, level {1-3} */
+                    si_signo = TARGET_SIGSEGV;
+                    si_code = TARGET_SEGV_ACCERR;
+                    break;
+                case 0x11: /* Synchronous Tag Check Fault */
+                    si_signo = TARGET_SIGSEGV;
+                    si_code = TARGET_SEGV_MTESERR;
+                    break;
+                case 0x21: /* Alignment fault */
+                    si_signo = TARGET_SIGBUS;
+                    si_code = TARGET_BUS_ADRALN;
+                    break;
+                default:
+                    g_assert_not_reached();
+                }
                 break;
-            case 0x09 ... 0x0b: /* Access flag fault, level {1-3} */
-            case 0x0d ... 0x0f: /* Permission fault, level {1-3} */
-                si_signo = TARGET_SIGSEGV;
-                si_code = TARGET_SEGV_ACCERR;
-                break;
-            case 0x11: /* Synchronous Tag Check Fault */
-                si_signo = TARGET_SIGSEGV;
-                si_code = TARGET_SEGV_MTESERR;
-                break;
-            case 0x21: /* Alignment fault */
+            case EC_PCALIGNMENT:
                 si_signo = TARGET_SIGBUS;
                 si_code = TARGET_BUS_ADRALN;
                 break;
diff --git a/target/arm/tlb_helper.c b/target/arm/tlb_helper.c
index 4cacb9658f..b79004e0cc 100644
--- a/target/arm/tlb_helper.c
+++ b/target/arm/tlb_helper.c
@@ -9,6 +9,7 @@
 #include "cpu.h"
 #include "internals.h"
 #include "exec/exec-all.h"
+#include "exec/helper-proto.h"
 
 static inline uint32_t merge_syn_data_abort(uint32_t template_syn,
                                             unsigned int target_el,
@@ -134,6 +135,23 @@ void arm_cpu_do_unaligned_access(CPUState *cs, vaddr vaddr,
     arm_deliver_fault(cpu, vaddr, access_type, mmu_idx, &fi);
 }
 
+void helper_exception_pc_alignment(CPUARMState *env, target_ulong pc)
+{
+    ARMMMUFaultInfo fi = { .type = ARMFault_Alignment };
+    int target_el = exception_target_el(env);
+    int mmu_idx = cpu_mmu_index(env, true);
+    uint32_t fsc;
+
+    env->exception.vaddress = pc;
+
+    /*
+     * Note that the fsc is not applicable to this exception,
+     * since any syndrome is pcalignment not insn_abort.
+     */
+    env->exception.fsr = compute_fsr_fsc(env, &fi, target_el, mmu_idx, &fsc);
+    raise_exception(env, EXCP_PREFETCH_ABORT, syn_pcalignment(), target_el);
+}
+
 #if !defined(CONFIG_USER_ONLY)
 
 /*
diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 2986fe1393..130a9ff8d5 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -14753,6 +14753,7 @@ static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
     uint64_t pc = s->base.pc_next;
     uint32_t insn;
 
+    /* Singlestep exceptions have the highest priority. */
     if (s->ss_active && !s->pstate_ss) {
         /* Singlestep state is Active-pending.
          * If we're in this state at the start of a TB then either
@@ -14771,6 +14772,20 @@ static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
         return;
     }
 
+    if (pc & 3) {
+        /*
+         * PC alignment fault.  This has priority over the instruction abort
+         * that we would receive from a translation fault via arm_ldl_code.
+         * This should only be possible after an indirect branch, at the
+         * start of the TB.
+         */
+        assert(s->base.num_insns == 1);
+        gen_helper_exception_pc_alignment(cpu_env, tcg_constant_tl(pc));
+        s->base.is_jmp = DISAS_NORETURN;
+        s->base.pc_next = QEMU_ALIGN_UP(pc, 4);
+        return;
+    }
+
     s->pc_curr = pc;
     insn = arm_ldl_code(env, &s->base, pc, s->sctlr_b);
     s->insn = insn;
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 82d4e24c27..828fb328ee 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9566,7 +9566,27 @@ static void arm_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
     uint32_t pc = dc->base.pc_next;
     unsigned int insn;
 
-    if (arm_check_ss_active(dc) || arm_check_kernelpage(dc)) {
+    /* Singlestep exceptions have the highest priority. */
+    if (arm_check_ss_active(dc)) {
+        dc->base.pc_next = pc + 4;
+        return;
+    }
+
+    if (pc & 3) {
+        /*
+         * PC alignment fault.  This has priority over the instruction abort
+         * that we would receive from a translation fault via arm_ldl_code
+         * (or the execution of the kernelpage entrypoint). This should only
+         * be possible after an indirect branch, at the start of the TB.
+         */
+        assert(dc->base.num_insns == 1);
+        gen_helper_exception_pc_alignment(cpu_env, tcg_constant_tl(pc));
+        dc->base.is_jmp = DISAS_NORETURN;
+        dc->base.pc_next = QEMU_ALIGN_UP(pc, 4);
+        return;
+    }
+
+    if (arm_check_kernelpage(dc)) {
         dc->base.pc_next = pc + 4;
         return;
     }
-- 
2.25.1

[PATCH v4 08/10] target/arm: Assert thumb pc is aligned

[Richard Henderson]

Misaligned thumb PC is architecturally impossible.
Assert is better than proceeding, in case we've missed
something somewhere.

Expand a comment about aligning the pc in gdbstub.
Fail an incoming migrate if a thumb pc is misaligned.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/gdbstub.c   |  9 +++++++--
 target/arm/machine.c   | 10 ++++++++++
 target/arm/translate.c |  3 +++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/target/arm/gdbstub.c b/target/arm/gdbstub.c
index e0dcb33e32..90bf803be2 100644
--- a/target/arm/gdbstub.c
+++ b/target/arm/gdbstub.c
@@ -77,8 +77,13 @@ int arm_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
 
     tmp = ldl_p(mem_buf);
 
-    /* Mask out low bit of PC to workaround gdb bugs.  This will probably
-       cause problems if we ever implement the Jazelle DBX extensions.  */
+    /*
+     * Mask out low bits of PC to workaround gdb bugs.
+     * This avoids an assert in thumb_tr_translate_insn, because it is
+     * architecturally impossible to misalign the pc.
+     * This will probably cause problems if we ever implement the
+     * Jazelle DBX extensions.
+     */
     if (n == 15) {
         tmp &= ~1;
     }
diff --git a/target/arm/machine.c b/target/arm/machine.c
index c74d8c3f4b..135d2420b5 100644
--- a/target/arm/machine.c
+++ b/target/arm/machine.c
@@ -794,6 +794,16 @@ static int cpu_post_load(void *opaque, int version_id)
             return -1;
         }
     }
+
+    /*
+     * Misaligned thumb pc is architecturally impossible.
+     * We have an assert in thumb_tr_translate_insn to verify this.
+     * Fail an incoming migrate to avoid this assert.
+     */
+    if (!is_a64(env) && env->thumb && (env->regs[15] & 1)) {
+        return -1;
+    }
+
     if (!kvm_enabled()) {
         pmu_op_finish(&cpu->env);
     }
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 828fb328ee..9ac4292cfb 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -9657,6 +9657,9 @@ static void thumb_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
     uint32_t insn;
     bool is_16bit;
 
+    /* Misaligned thumb PC is architecturally impossible. */
+    assert((dc->base.pc_next & 1) == 0);
+
     if (arm_check_ss_active(dc) || arm_check_kernelpage(dc)) {
         dc->base.pc_next = pc + 2;
         return;
-- 
2.25.1

[PATCH v4 09/10] target/arm: Suppress bp for exceptions with more priority

[Richard Henderson]

Both single-step and pc alignment faults have priority over
breakpoint exceptions.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/debug_helper.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/target/arm/debug_helper.c b/target/arm/debug_helper.c
index 2983e36dd3..32f3caec23 100644
--- a/target/arm/debug_helper.c
+++ b/target/arm/debug_helper.c
@@ -220,6 +220,7 @@ bool arm_debug_check_breakpoint(CPUState *cs)
 {
     ARMCPU *cpu = ARM_CPU(cs);
     CPUARMState *env = &cpu->env;
+    target_ulong pc;
     int n;
 
     /*
@@ -231,6 +232,28 @@ bool arm_debug_check_breakpoint(CPUState *cs)
         return false;
     }
 
+    /*
+     * Single-step exceptions have priority over breakpoint exceptions.
+     * If single-step state is active-pending, suppress the bp.
+     */
+    if (arm_singlestep_active(env) && !(env->pstate & PSTATE_SS)) {
+        return false;
+    }
+
+    /*
+     * PC alignment faults have priority over breakpoint exceptions.
+     */
+    pc = is_a64(env) ? env->pc : env->regs[15];
+    if ((is_a64(env) || !env->thumb) && (pc & 3) != 0) {
+        return false;
+    }
+
+    /*
+     * Instruction aborts have priority over breakpoint exceptions.
+     * TODO: We would need to look up the page for PC and verify that
+     * it is present and executable.
+     */
+
     for (n = 0; n < ARRAY_SIZE(env->cpu_breakpoint); n++) {
         if (bp_wp_matches(cpu, n, false)) {
             return true;
-- 
2.25.1

[PATCH v4 10/10] tests/tcg: Add arm and aarch64 pc alignment tests

[Richard Henderson]

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tests/tcg/aarch64/pcalign-a64.c   | 37 +++++++++++++++++++++++++
 tests/tcg/arm/pcalign-a32.c       | 46 +++++++++++++++++++++++++++++++
 tests/tcg/aarch64/Makefile.target |  4 +--
 tests/tcg/arm/Makefile.target     |  4 +++
 4 files changed, 89 insertions(+), 2 deletions(-)
 create mode 100644 tests/tcg/aarch64/pcalign-a64.c
 create mode 100644 tests/tcg/arm/pcalign-a32.c

diff --git a/tests/tcg/aarch64/pcalign-a64.c b/tests/tcg/aarch64/pcalign-a64.c
new file mode 100644
index 0000000000..6b9277f919
--- /dev/null
+++ b/tests/tcg/aarch64/pcalign-a64.c
@@ -0,0 +1,37 @@
+/* Test PC misalignment exception */
+
+#include <assert.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+static void *expected;
+
+static void sigbus(int sig, siginfo_t *info, void *vuc)
+{
+    assert(info->si_code == BUS_ADRALN);
+    assert(info->si_addr == expected);
+    exit(EXIT_SUCCESS);
+}
+
+int main()
+{
+    void *tmp;
+
+    struct sigaction sa = {
+        .sa_sigaction = sigbus,
+        .sa_flags = SA_SIGINFO
+    };
+
+    if (sigaction(SIGBUS, &sa, NULL) < 0) {
+        perror("sigaction");
+        return EXIT_FAILURE;
+    }
+
+    asm volatile("adr %0, 1f + 1\n\t"
+                 "str %0, %1\n\t"
+                 "br  %0\n"
+                 "1:"
+                 : "=&r"(tmp), "=m"(expected));
+    abort();
+}
diff --git a/tests/tcg/arm/pcalign-a32.c b/tests/tcg/arm/pcalign-a32.c
new file mode 100644
index 0000000000..3c9c8cc97b
--- /dev/null
+++ b/tests/tcg/arm/pcalign-a32.c
@@ -0,0 +1,46 @@
+/* Test PC misalignment exception */
+
+#ifdef __thumb__
+#error "This test must be compiled for ARM"
+#endif
+
+#include <assert.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+static void *expected;
+
+static void sigbus(int sig, siginfo_t *info, void *vuc)
+{
+    assert(info->si_code == BUS_ADRALN);
+    assert(info->si_addr == expected);
+    exit(EXIT_SUCCESS);
+}
+
+int main()
+{
+    void *tmp;
+
+    struct sigaction sa = {
+        .sa_sigaction = sigbus,
+        .sa_flags = SA_SIGINFO
+    };
+
+    if (sigaction(SIGBUS, &sa, NULL) < 0) {
+        perror("sigaction");
+        return EXIT_FAILURE;
+    }
+
+    asm volatile("adr %0, 1f + 2\n\t"
+                 "str %0, %1\n\t"
+                 "bx  %0\n"
+                 "1:"
+                 : "=&r"(tmp), "=m"(expected));
+
+    /*
+     * From v8, it is CONSTRAINED UNPREDICTABLE whether BXWritePC aligns
+     * the address or not.  If so, we can legitimately fall through.
+     */
+    return EXIT_SUCCESS;
+}
diff --git a/tests/tcg/aarch64/Makefile.target b/tests/tcg/aarch64/Makefile.target
index 2c05c90d17..1d967901bd 100644
--- a/tests/tcg/aarch64/Makefile.target
+++ b/tests/tcg/aarch64/Makefile.target
@@ -8,8 +8,8 @@ VPATH 		+= $(ARM_SRC)
 AARCH64_SRC=$(SRC_PATH)/tests/tcg/aarch64
 VPATH 		+= $(AARCH64_SRC)
 
-# Float-convert Tests
-AARCH64_TESTS=fcvt
+# Base architecture tests
+AARCH64_TESTS=fcvt pcalign-a64
 
 fcvt: LDFLAGS+=-lm
 
diff --git a/tests/tcg/arm/Makefile.target b/tests/tcg/arm/Makefile.target
index 5ab59ed6ce..f509d823d4 100644
--- a/tests/tcg/arm/Makefile.target
+++ b/tests/tcg/arm/Makefile.target
@@ -29,6 +29,10 @@ run-fcvt: fcvt
 	$(call run-test,fcvt,$(QEMU) $<,"$< on $(TARGET_NAME)")
 	$(call diff-out,fcvt,$(ARM_SRC)/fcvt.ref)
 
+# PC alignment test
+ARM_TESTS += pcalign-a32
+pcalign-a32: CFLAGS+=-marm
+
 ifeq ($(CONFIG_ARM_COMPATIBLE_SEMIHOSTING),y)
 
 # Semihosting smoke test for linux-user
-- 
2.25.1

Re: [PATCH v4 03/10] target/arm: Hoist pc_next to a local variable in thumb_tr_translate_insn

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:04, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/translate.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

Re: [PATCH v4 01/10] target/arm: Hoist pc_next to a local variable in aarch64_tr_translate_insn

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:04, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/translate-a64.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

Re: [PATCH v4 02/10] target/arm: Hoist pc_next to a local variable in arm_tr_translate_insn

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:07, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/translate.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

Re: [PATCH v4 04/10] target/arm: Split arm_pre_translate_insn

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:07, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Create arm_check_ss_active and arm_check_kernelpage.
>
> Reverse the order of the tests.  While it doesn't matter in practice,
> because only user-only has a kernel page and user-only never sets
> ss_active, ss_active has priority over execution exceptions and it
> is best to keep them in the proper order.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

Re: [PATCH v4 05/10] target/arm: Advance pc for arch single-step exception

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:09, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> The size of the code covered by a TranslationBlock cannot be 0;
> this is checked via assert in tb_gen_code.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/translate-a64.c | 1 +
>  1 file changed, 1 insertion(+)
>

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

Re: [PATCH v4 06/10] target/arm: Split compute_fsr_fsc out of arm_deliver_fault

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:09, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> We will reuse this section of arm_deliver_fault for
> raising pc alignment faults.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

Re: [PATCH v4 07/10] target/arm: Take an exception if PC is misaligned

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:11, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> For A64, any input to an indirect branch can cause this.
>
> For A32, many indirect branch paths force the branch to be aligned,
> but BXWritePC does not.  This includes the BX instruction but also
> other interworking changes to PC.  Prior to v8, this case is UNDEFINED.
> With v8, this is CONSTRAINED UNPREDICTABLE and may either raise an
> exception or force align the PC.
>
> We choose to raise an exception because we have the infrastructure,
> it makes the generated code for gen_bx simpler, and it has the
> possibility of catching more guest bugs.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM

Re: [PATCH v4 00/10] target/arm: Fix insn exception priorities

[Peter Maydell]

On Wed, 3 Nov 2021 at 04:04, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Raise pc alignment faults.
> Fix single-step and pc-align priority over breakpoints.
> Not yet fixing insn abort priority over breakpoints.

Do you have a view on whether we should put this into 6.2
or hold it for 7.0 ?

-- PMM

Re: [PATCH v4 00/10] target/arm: Fix insn exception priorities

[Richard Henderson]

On 11/8/21 3:16 PM, Peter Maydell wrote:
> On Wed, 3 Nov 2021 at 04:04, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> Raise pc alignment faults.
>> Fix single-step and pc-align priority over breakpoints.
>> Not yet fixing insn abort priority over breakpoints.
> 
> Do you have a view on whether we should put this into 6.2
> or hold it for 7.0 ?

I think it's safe enough to go in.
But it's something that has been broken since forever, so it could also wait.


r~