target/mips: Use an exception for semihosting

Within do_interrupt, we hold the iothread lock, which
is required for Chardev access for the console, and for
the round trip for use_gdb_syscalls().

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/mips/cpu.h

@@ -1252,8 +1252,9 @@ enum {
     EXCP_MSAFPE,
     EXCP_TLBXI,
     EXCP_TLBRI,
+    EXCP_SEMIHOST,
 
-    EXCP_LAST = EXCP_TLBRI,
+    EXCP_LAST = EXCP_SEMIHOST,
 };
 
 /*

target/mips/tcg/exception.c

@@ -125,6 +125,7 @@ static const char * const excp_names[EXCP_LAST + 1] = {
     [EXCP_TLBRI] = "TLB read-inhibit",
     [EXCP_MSADIS] = "MSA disabled",
     [EXCP_MSAFPE] = "MSA floating point",
+    [EXCP_SEMIHOST] = "Semihosting",
 };
 
 const char *mips_exception_name(int32_t exception)

target/mips/tcg/micromips_translate.c.inc

@@ -826,7 +826,7 @@ static void gen_pool16c_insn(DisasContext *ctx)
         break;
     case SDBBP16:
         if (is_uhi(extract32(ctx->opcode, 0, 4))) {
-            gen_helper_do_semihosting(cpu_env);
+            generate_exception_end(ctx, EXCP_SEMIHOST);
         } else {
             /*
              * XXX: not clear which exception should be raised
@@ -942,7 +942,7 @@ static void gen_pool16c_r6_insn(DisasContext *ctx)
         case R6_SDBBP16:
             /* SDBBP16 */
             if (is_uhi(extract32(ctx->opcode, 6, 4))) {
-                gen_helper_do_semihosting(cpu_env);
+                generate_exception_end(ctx, EXCP_SEMIHOST);
             } else {
                 if (ctx->hflags & MIPS_HFLAG_SBRI) {
                     generate_exception(ctx, EXCP_RI);
@@ -1311,7 +1311,7 @@ static void gen_pool32axf(CPUMIPSState *env, DisasContext *ctx, int rt, int rs)
             break;
         case SDBBP:
             if (is_uhi(extract32(ctx->opcode, 16, 10))) {
-                gen_helper_do_semihosting(cpu_env);
+                generate_exception_end(ctx, EXCP_SEMIHOST);
             } else {
                 check_insn(ctx, ISA_MIPS_R1);
                 if (ctx->hflags & MIPS_HFLAG_SBRI) {

target/mips/tcg/mips16e_translate.c.inc

@@ -952,7 +952,7 @@ static int decode_ase_mips16e(CPUMIPSState *env, DisasContext *ctx)
             break;
         case RR_SDBBP:
             if (is_uhi(extract32(ctx->opcode, 5, 6))) {
-                gen_helper_do_semihosting(cpu_env);
+                generate_exception_end(ctx, EXCP_SEMIHOST);
             } else {
                 /*
                  * XXX: not clear which exception should be raised

target/mips/tcg/nanomips_translate.c.inc

@@ -3695,7 +3695,7 @@ static int decode_nanomips_32_48_opc(CPUMIPSState *env, DisasContext *ctx)
                 break;
             case NM_SDBBP:
                 if (is_uhi(extract32(ctx->opcode, 0, 19))) {
-                    gen_helper_do_semihosting(cpu_env);
+                    generate_exception_end(ctx, EXCP_SEMIHOST);
                 } else {
                     if (ctx->hflags & MIPS_HFLAG_SBRI) {
                         gen_reserved_instruction(ctx);
@@ -4634,7 +4634,7 @@ static int decode_isa_nanomips(CPUMIPSState *env, DisasContext *ctx)
                 break;
             case NM_SDBBP16:
                 if (is_uhi(extract32(ctx->opcode, 0, 3))) {
-                    gen_helper_do_semihosting(cpu_env);
+                    generate_exception_end(ctx, EXCP_SEMIHOST);
                 } else {
                     if (ctx->hflags & MIPS_HFLAG_SBRI) {
                         gen_reserved_instruction(ctx);

target/mips/tcg/sysemu/mips-semi.c

@@ -20,10 +20,10 @@
 #include "qemu/osdep.h"
 #include "cpu.h"
 #include "qemu/log.h"
-#include "exec/helper-proto.h"
 #include "semihosting/softmmu-uaccess.h"
 #include "semihosting/semihost.h"
 #include "semihosting/console.h"
+#include "internal.h"
 
 typedef enum UHIOp {
     UHI_exit = 1,
@@ -238,7 +238,7 @@ static int copy_argn_to_target(CPUMIPSState *env, int arg_num,
         unlock_user(p, gpr, 0);                 \
     } while (0)
 
-void helper_do_semihosting(CPUMIPSState *env)
+void mips_semihosting(CPUMIPSState *env)
 {
     target_ulong *gpr = env->active_tc.gpr;
     const UHIOp op = gpr[25];

target/mips/tcg/sysemu/tlb_helper.c

@@ -1053,6 +1053,10 @@ void mips_cpu_do_interrupt(CPUState *cs)
     }
     offset = 0x180;
     switch (cs->exception_index) {
+    case EXCP_SEMIHOST:
+        cs->exception_index = EXCP_NONE;
+        mips_semihosting(env);
+        return;
     case EXCP_DSS:
         env->CP0_Debug |= 1 << CP0DB_DSS;
         /*

target/mips/tcg/sysemu_helper.h.inc

@@ -9,8 +9,6 @@
  * SPDX-License-Identifier: LGPL-2.1-or-later
  */
 
-DEF_HELPER_1(do_semihosting, void, env)
-
 /* CP0 helpers */
 DEF_HELPER_1(mfc0_mvpcontrol, tl, env)
 DEF_HELPER_1(mfc0_mvpconf0, tl, env)

target/mips/tcg/tcg-internal.h

@@ -62,6 +62,8 @@ bool mips_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
                        MMUAccessType access_type, int mmu_idx,
                        bool probe, uintptr_t retaddr);
 
+void mips_semihosting(CPUMIPSState *env);
+
 #endif /* !CONFIG_USER_ONLY */
 
 #endif

target/mips/tcg/translate.c

@@ -12094,14 +12094,6 @@ static inline bool is_uhi(int sdbbp_code)
 #endif
 }
 
-#ifdef CONFIG_USER_ONLY
-/* The above should dead-code away any calls to this..*/
-static inline void gen_helper_do_semihosting(void *env)
-{
-    g_assert_not_reached();
-}
-#endif
-
 void gen_ldxs(DisasContext *ctx, int base, int index, int rd)
 {
     TCGv t0 = tcg_temp_new();
@@ -13910,7 +13902,7 @@ static void decode_opc_special_r6(CPUMIPSState *env, DisasContext *ctx)
         break;
     case R6_OPC_SDBBP:
         if (is_uhi(extract32(ctx->opcode, 6, 20))) {
-            gen_helper_do_semihosting(cpu_env);
+            generate_exception_end(ctx, EXCP_SEMIHOST);
         } else {
             if (ctx->hflags & MIPS_HFLAG_SBRI) {
                 gen_reserved_instruction(ctx);
@@ -14322,7 +14314,7 @@ static void decode_opc_special2_legacy(CPUMIPSState *env, DisasContext *ctx)
         break;
     case OPC_SDBBP:
         if (is_uhi(extract32(ctx->opcode, 6, 20))) {
-            gen_helper_do_semihosting(cpu_env);
+            generate_exception_end(ctx, EXCP_SEMIHOST);
         } else {
             /*
              * XXX: not clear which exception should be raised