target-arm: Implement new HLT trap for semihosting

Version 2.0 of the semihosting specification introduces new trap
instructions for AArch32: HLT 0xF000 for A32 and HLT 0x3C for T32.
Implement these (in the same way we implement the existing HLT
semihosting trap for A64).

The old traps via SVC and BKPT are unaffected.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1476792973-18508-1-git-send-email-peter.maydell@linaro.org

diff --git a/linux-user/main.c b/linux-user/main.c
index c6f2e20c097c075e5c393aab17487fcbec81397d..54970bc4d9062c86e3e987364ae11fd593c475b5 100644 (file)
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -806,6 +806,9 @@ void cpu_loop(CPUARMState *env)
                 }
             }
             break;
+        case EXCP_SEMIHOST:
+            env->regs[0] = do_arm_semihosting(env);
+            break;
         case EXCP_INTERRUPT:
             /* just indicate that signals should be handled asap */
             break;

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 66953900755311f11a54cedf2a1bf25e3f8f4c92..9d75227e044adb7310a7a41f543da089ed33726c 100644 (file)
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -52,7 +52,7 @@
 #define EXCP_SMC            13   /* Secure Monitor Call */
 #define EXCP_VIRQ           14
 #define EXCP_VFIQ           15
-#define EXCP_SEMIHOST       16   /* semihosting call (A64 only) */
+#define EXCP_SEMIHOST       16   /* semihosting call */
 
 #define ARMV7M_EXCP_RESET   1
 #define ARMV7M_EXCP_NMI     2

diff --git a/target-arm/helper.c b/target-arm/helper.c
index cb83ee2008864fa423b31ca61f74a2e8b288ccd3..25b15dc100fc8319cbd95be0020229ea040c7b10 100644 (file)
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -6573,12 +6573,19 @@ static inline bool check_for_semihosting(CPUState *cs)
         /* Only intercept calls from privileged modes, to provide some
          * semblance of security.
          */
-        if (!semihosting_enabled() ||
-            ((env->uncached_cpsr & CPSR_M) == ARM_CPU_MODE_USR)) {
+        if (cs->exception_index != EXCP_SEMIHOST &&
+            (!semihosting_enabled() ||
+             ((env->uncached_cpsr & CPSR_M) == ARM_CPU_MODE_USR))) {
             return false;
         }
 
         switch (cs->exception_index) {
+        case EXCP_SEMIHOST:
+            /* This is always a semihosting call; the "is this usermode"
+             * and "is semihosting enabled" checks have been done at
+             * translate time.
+             */
+            break;
         case EXCP_SWI:
             /* Check for semihosting interrupt.  */
             if (env->thumb) {

diff --git a/target-arm/translate.c b/target-arm/translate.c
index 164b52a0d0683c46e56fc288ec353200c021f8c2..ef62f8b0c4309f142e577f96ddf70babc67fa6f5 100644 (file)
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -28,6 +28,7 @@
 #include "qemu/log.h"
 #include "qemu/bitops.h"
 #include "arm_ldst.h"
+#include "exec/semihost.h"
 
 #include "exec/helper-proto.h"
 #include "exec/helper-gen.h"
@@ -1144,6 +1145,33 @@ static inline void gen_lookup_tb(DisasContext *s)
     s->is_jmp = DISAS_JUMP;
 }
 
+static inline void gen_hlt(DisasContext *s, int imm)
+{
+    /* HLT. This has two purposes.
+     * Architecturally, it is an external halting debug instruction.
+     * Since QEMU doesn't implement external debug, we treat this as
+     * it is required for halting debug disabled: it will UNDEF.
+     * Secondly, "HLT 0x3C" is a T32 semihosting trap instruction,
+     * and "HLT 0xF000" is an A32 semihosting syscall. These traps
+     * must trigger semihosting even for ARMv7 and earlier, where
+     * HLT was an undefined encoding.
+     * In system mode, we don't allow userspace access to
+     * semihosting, to provide some semblance of security
+     * (and for consistency with our 32-bit semihosting).
+     */
+    if (semihosting_enabled() &&
+#ifndef CONFIG_USER_ONLY
+        s->current_el != 0 &&
+#endif
+        (imm == (s->thumb ? 0x3c : 0xf000))) {
+        gen_exception_internal_insn(s, 0, EXCP_SEMIHOST);
+        return;
+    }
+
+    gen_exception_insn(s, s->thumb ? 2 : 4, EXCP_UDEF, syn_uncategorized(),
+                       default_exception_el(s));
+}
+
 static inline void gen_add_data_offset(DisasContext *s, unsigned int insn,
                                        TCGv_i32 var)
 {
@@ -8395,6 +8423,10 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
         {
             int imm16 = extract32(insn, 0, 4) | (extract32(insn, 8, 12) << 4);
             switch (op1) {
+            case 0:
+                /* HLT */
+                gen_hlt(s, imm16);
+                break;
             case 1:
                 /* bkpt */
                 ARCH(5);
@@ -8419,7 +8451,7 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
                 gen_smc(s);
                 break;
             default:
-                goto illegal_op;
+                g_assert_not_reached();
             }
             break;
         }
@@ -11451,19 +11483,33 @@ static void disas_thumb_insn(CPUARMState *env, DisasContext *s)
             break;
         }
 
-        case 0xa: /* rev */
+        case 0xa: /* rev, and hlt */
+        {
+            int op1 = extract32(insn, 6, 2);
+
+            if (op1 == 2) {
+                /* HLT */
+                int imm6 = extract32(insn, 0, 6);
+
+                gen_hlt(s, imm6);
+                break;
+            }
+
+            /* Otherwise this is rev */
             ARCH(6);
             rn = (insn >> 3) & 0x7;
             rd = insn & 0x7;
             tmp = load_reg(s, rn);
-            switch ((insn >> 6) & 3) {
+            switch (op1) {
             case 0: tcg_gen_bswap32_i32(tmp, tmp); break;
             case 1: gen_rev16(tmp); break;
             case 3: gen_revsh(tmp); break;
-            default: goto illegal_op;
+            default:
+                g_assert_not_reached();
             }
             store_reg(s, rd, tmp);
             break;
+        }
 
         case 6:
             switch ((insn >> 5) & 7) {