cpu: Move icount_decr to CPUNegativeOffsetState

Amusingly, we had already ignored the comment to keep this value
at the end of CPUState. This restores the minimum negative offset
from TCG_AREG0 for code generation.

For the couple of uses within qom/cpu.c, without NEED_CPU_H, add
a pointer from the CPUState object to the IcountDecr object within
CPUNegativeOffsetState.

Backports commit 5e1401969b25f676fee6b1c564441759cf967a43 from qemu

qemu/accel/tcg/cpu-exec.c

@@ -442,14 +442,14 @@ static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 #ifdef CONFIG_USER_ONLY
         abort();
 #else
-        int insns_left = cpu->icount_decr.u32;
+        int insns_left = atomic_read(&cpu_neg(cpu)->icount_decr.u32);
         *last_tb = NULL;
         if (cpu->icount_extra && insns_left >= 0) {
             /* Refill decrementer and continue execution.  */
             cpu->icount_extra += insns_left;
             insns_left = MIN(0xffff, cpu->icount_extra);
             cpu->icount_extra -= insns_left;
-            cpu->icount_decr.u16.low = insns_left;
+            cpu_neg(cpu)->icount_decr.u16.low = insns_left;
         } else {
             if (insns_left > 0) {
                 /* Execute remaining instructions.  */

qemu/accel/tcg/translate-all.c

@@ -315,13 +315,15 @@ static int cpu_restore_state_from_tb(CPUState *cpu, TranslationBlock *tb,
     return -1;
 
 found:
-    // UNICORN: Commented out
+    // UNICORN: If'd out
-    //if (reset_icount && (tb_cflags(tb) & CF_USE_ICOUNT)) {
+#if 0
-    //    assert(use_icount);
+    if (reset_icount && (tb_cflags(tb) & CF_USE_ICOUNT)) {
-    //    /* Reset the cycle counter to the start of the block
+        assert(use_icount);
-    //       and shift if to the number of actually executed instructions */
+        /* Reset the cycle counter to the start of the block
-    //    cpu->icount_decr.u16.low += num_insns - i;
+           and shift if to the number of actually executed instructions */
-    //}
+        cpu_neg(cpu)->icount_decr.u16.low += num_insns - i;
+    }
+#endif
     restore_state_to_opc(env, tb, data);
 
 #ifdef CONFIG_PROFILER
@@ -1865,11 +1867,11 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
         cpu_abort(cpu, "cpu_io_recompile: could not find TB for pc=%p",
                   (void *)retaddr);
     }
-    n = cpu->icount_decr.u16.low + tb->icount;
+    n = cpu_neg(cpu)->icount_decr.u16.low + tb->icount;
     cpu_restore_state_from_tb(cpu, tb, retaddr, true);
     /* Calculate how many instructions had been executed before the fault
        occurred.  */
-    n = n - cpu->icount_decr.u16.low;
+    n = n - cpu_neg(cpu)->icount_decr.u16.low;
     /* Generate a new TB ending on the I/O insn.  */
     n++;
     /* On MIPS and SH, delay slot instructions can only be restarted if
@@ -1879,14 +1881,14 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
 #if defined(TARGET_MIPS)
     if ((env->hflags & MIPS_HFLAG_BMASK) != 0 && n > 1) {
         env->active_tc.PC -= (env->hflags & MIPS_HFLAG_B16 ? 2 : 4);
-        cpu->icount_decr.u16.low++;
+        cpu_neg(cpu)->icount_decr.u16.low++;
         env->hflags &= ~MIPS_HFLAG_BMASK;
     }
 #elif defined(TARGET_SH4)
     if ((env->flags & ((DELAY_SLOT | DELAY_SLOT_CONDITIONAL))) != 0
             && n > 1) {
         env->pc -= 2;
-        cpu->icount_decr.u16.low++;
+        cpu_neg(cpu)->icount_decr.u16.low++;
         env->flags &= ~(DELAY_SLOT | DELAY_SLOT_CONDITIONAL);
     }
 #endif
@@ -2003,6 +2005,7 @@ void cpu_interrupt(CPUState *cpu, int mask)
 {
     cpu->interrupt_request |= mask;
     cpu->tcg_exit_req = 1;
+    atomic_set(&cpu_neg(cpu)->icount_decr.u16.high, -1);
 }
 
 #if 0

qemu/include/exec/cpu-all.h

@@ -384,6 +384,7 @@ int cpu_exec(struct uc_struct *uc, CPUState *cpu);
 static inline void cpu_set_cpustate_pointers(ArchCPU *cpu)
 {
     cpu->parent_obj.env_ptr = &cpu->env;
+    cpu->parent_obj.icount_decr_ptr = &cpu->neg.icount_decr;
 }
 
 /**

qemu/include/exec/cpu-defs.h

@@ -34,6 +34,7 @@
 #include "exec/hwaddr.h"
 #endif
 #include "exec/memattrs.h"
+#include "qom/cpu.h"
 
 #include "cpu-param.h"
 
@@ -220,7 +221,7 @@ typedef struct CPUTLBDesc {
  * before CPUArchState, as a field named "neg".
  */
 typedef struct CPUNegativeOffsetState {
-    /* Empty */
+    IcountDecr icount_decr;
 } CPUNegativeOffsetState;
 
 #endif

qemu/include/exec/gen-icount.h

@@ -5,8 +5,6 @@
 
 /* Helpers for instruction counting code generation.  */
 
-#define ENV_OFFSET   offsetof(ArchCPU, env)
-
 //static TCGOp *icount_start_insn;
 
 static inline void gen_tb_start(TCGContext *tcg_ctx, TranslationBlock *tb)
@@ -17,7 +15,7 @@ static inline void gen_tb_start(TCGContext *tcg_ctx, TranslationBlock *tb)
     tcg_ctx->exitreq_label = gen_new_label(tcg_ctx);
     flag = tcg_temp_new_i32(tcg_ctx);
     tcg_gen_ld_i32(tcg_ctx, flag, tcg_ctx->cpu_env,
-                   offsetof(CPUState, tcg_exit_req) - ENV_OFFSET);
+                   offsetof(CPUState, tcg_exit_req) - offsetof(ArchCPU, env));
     tcg_gen_brcondi_i32(tcg_ctx, TCG_COND_NE, flag, 0, tcg_ctx->exitreq_label);
     tcg_temp_free_i32(tcg_ctx, flag);
 
@@ -30,7 +28,8 @@ static inline void gen_tb_start(TCGContext *tcg_ctx, TranslationBlock *tb)
     }
 
     tcg_gen_ld_i32(tcg_ctx, count, tcg_ctx->cpu_env,
-                   -ENV_OFFSET + offsetof(CPUState, icount_decr.u32));
+                   offsetof(ArchCPU, neg.icount_decr.u32) -
+                   offsetof(ArchCPU, env));
 
     if (tb_cflags(tb) & CF_USE_ICOUNT) {
         imm = tcg_temp_new_i32(tcg_ctx);
@@ -48,7 +47,8 @@ static inline void gen_tb_start(TCGContext *tcg_ctx, TranslationBlock *tb)
 
     if (tb_cflags(tb) & CF_USE_ICOUNT) {
         tcg_gen_st16_i32(tcg_ctx, count, tcg_ctx, cpu_env,
-                         -ENV_OFFSET + offsetof(CPUState, icount_decr.u16.low));
+                         offsetof(ArchCPU, neg.icount_decr.u16.low) -
+                         offsetof(ArchCPU, env));
     }
 
     tcg_temp_free_i32(tcg_ctx, count);
@@ -69,20 +69,26 @@ static inline void gen_tb_end(TCGContext *tcg_ctx, TranslationBlock *tb, int num
     tcg_gen_exit_tb(tcg_ctx, tb, TB_EXIT_REQUESTED);
 }
 
-#if 0
 static inline void gen_io_start(TCGContext *tcg_ctx)
 {
+#if 0
     TCGv_i32 tmp = tcg_const_i32(tcg_ctx, 1);
-    tcg_gen_st_i32(tcg_ctx, tmp, tcg_ctx->tcg_env, -ENV_OFFSET + offsetof(CPUState, can_do_io));
+    tcg_gen_st_i32(tcg_ctx, tmp, tcg_ctx->tcg_env,
+                   offsetof(ArchCPU, parent_obj.can_do_io) -
+                   offsetof(ArchCPU, env));
     tcg_temp_free_i32(tcg_ctx, tmp);
+#endif
 }
 
 static inline void gen_io_end(TCGContext *tcg_ctx)
 {
+#if 0
     TCGv_i32 tmp = tcg_const_i32(tcg_ctx, 0);
-    tcg_gen_st_i32(tcg_ctx, tmp, tcg_ctx->tcg_env, -ENV_OFFSET + offsetof(CPUState, can_do_io));
+    tcg_gen_st_i32(tcg_ctx, tmp, tcg_ctx->tcg_env,
+                   offsetof(ArchCPU, parent_obj.can_do_io) -
+                   offsetof(ArchCPU, env));
     tcg_temp_free_i32(tcg_ctx, tmp);
-}
 #endif
+}
 
 #endif

qemu/include/qom/cpu.h

@@ -189,17 +189,25 @@ typedef struct CPUClass {
     bool tcg_initialized;
 } CPUClass;
 
+/*
+ * Low 16 bits: number of cycles left, used only in icount mode.
+ * High 16 bits: Set to -1 to force TCG to stop executing linked TBs
+ * for this CPU and return to its top level loop (even in non-icount mode).
+ * This allows a single read-compare-cbranch-write sequence to test
+ * for both decrementer underflow and exceptions.
+ */
+typedef union IcountDecr {
+    uint32_t u32;
+    struct {
 #ifdef HOST_WORDS_BIGENDIAN
-typedef struct icount_decr_u16 {
+        uint16_t high;
-    uint16_t high;
+        uint16_t low;
-    uint16_t low;
-} icount_decr_u16;
 #else
-typedef struct icount_decr_u16 {
+        uint16_t low;
-    uint16_t low;
+        uint16_t high;
-    uint16_t high;
-} icount_decr_u16;
 #endif
+    } u16;
+} IcountDecr;
 
 typedef struct CPUBreakpoint {
     vaddr pc;
@@ -286,6 +294,7 @@ struct CPUAddressSpace {
  * @as: Pointer to the first AddressSpace, for the convenience of targets which
  *      only have a single AddressSpace
  * @env_ptr: Pointer to subclass-specific CPUArchState field.
+ * @icount_decr_ptr: Pointer to IcountDecr field within subclass.
  * @next_cpu: Next CPU sharing TB cache.
  * @opaque: User data.
  * @mem_io_pc: Host Program Counter at which the memory was accessed.
@@ -329,6 +338,7 @@ struct CPUState {
     MemoryRegion *memory;
 
     void *env_ptr; /* CPUArchState */
+    IcountDecr *icount_decr_ptr;
 
     /* Accessed in parallel; all accesses must be atomic */
     struct TranslationBlock *tb_jmp_cache[TB_JMP_CACHE_SIZE];
@@ -364,10 +374,6 @@ struct CPUState {
     int cpu_index;
     int cluster_index;
     uint32_t halted;
-    union {
-        uint32_t u32;
-        icount_decr_u16 u16;
-    } icount_decr;
     uint32_t can_do_io;
     int32_t exception_index;
 

qemu/qom/cpu.c

@@ -91,6 +91,7 @@ void cpu_exit(CPUState *cpu)
     /* Ensure cpu_exec will see the exit request after TCG has exited.  */
     smp_wmb();
     atomic_set(&cpu->tcg_exit_req, 1);
+    atomic_set(&cpu->icount_decr_ptr->u16.high, -1);
 }
 
 static void cpu_common_noop(CPUState *cpu)
@@ -145,7 +146,7 @@ static void cpu_common_reset(CPUState *cpu)
     cpu->mem_io_pc = 0;
     cpu->mem_io_vaddr = 0;
     cpu->icount_extra = 0;
-    atomic_set(&cpu->icount_decr.u32, 0);
+    atomic_set(&cpu->icount_decr_ptr->u32, 0);
     cpu->can_do_io = 0;
     cpu->exception_index = -1;
     cpu->crash_occurred = false;

qemu/tcg/tcg-op.c

@@ -2807,7 +2807,7 @@ void check_exit_request(TCGContext *tcg_ctx)
 
     flag = tcg_temp_new_i32(tcg_ctx);
     tcg_gen_ld_i32(tcg_ctx, flag, tcg_ctx->cpu_env,
-            offsetof(CPUState, tcg_exit_req) - ENV_OFFSET);
+            offsetof(CPUState, tcg_exit_req) - offsetof(ArchCPU, env));
     tcg_gen_brcondi_i32(tcg_ctx, TCG_COND_NE, flag, 0, tcg_ctx->exitreq_label);
     tcg_temp_free_i32(tcg_ctx, flag);
 }