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tcg: Clean up from 'next_tb'

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The value returned from tcg_qemu_tb_exec() is the value passed to the
corresponding tcg_gen_exit_tb() at translation time of the last TB
attempted to execute. It is a little confusing to store it in a variable
named 'next_tb'. In fact, it is a combination of 4-byte aligned pointer
and additional information in its two least significant bits. Break it
down right away into two variables named 'last_tb' and 'tb_exit' which
are a pointer to the last TB attempted to execute and the TB exit
reason, correspondingly. This simplifies the code and improves its
readability.

Correct a misleading documentation comment for tcg_qemu_tb_exec() and
fix logging in cpu_tb_exec(). Also rename a misleading 'next_tb' in
another couple of places.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Sergey Fedorov 2016-04-21 15:58:23 +03:00 committed by Richard Henderson
parent 7687bf52e5
commit 819af24b9c
4 changed files with 46 additions and 40 deletions
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59
cpu-exec.c
View File

@ -136,7 +136,9 @@ static void init_delay_params(SyncClocks *sc, const CPUState *cpu)
static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
{
CPUArchState *env = cpu->env_ptr;
uintptr_t next_tb;
uintptr_t ret;
TranslationBlock *last_tb;
int tb_exit;
uint8_t *tb_ptr = itb->tc_ptr;
qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
@ -160,36 +162,37 @@ static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
#endif /* DEBUG_DISAS */
cpu->can_do_io = !use_icount;
next_tb = tcg_qemu_tb_exec(env, tb_ptr);
ret = tcg_qemu_tb_exec(env, tb_ptr);
cpu->can_do_io = 1;
trace_exec_tb_exit((void *) (next_tb & ~TB_EXIT_MASK),
next_tb & TB_EXIT_MASK);
last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
tb_exit = ret & TB_EXIT_MASK;
trace_exec_tb_exit(last_tb, tb_exit);
if ((next_tb & TB_EXIT_MASK) > TB_EXIT_IDX1) {
if (tb_exit > TB_EXIT_IDX1) {
/* We didn't start executing this TB (eg because the instruction
* counter hit zero); we must restore the guest PC to the address
* of the start of the TB.
*/
CPUClass *cc = CPU_GET_CLASS(cpu);
TranslationBlock *tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
"Stopped execution of TB chain before %p ["
TARGET_FMT_lx "] %s\n",
itb->tc_ptr, itb->pc, lookup_symbol(itb->pc));
last_tb->tc_ptr, last_tb->pc,
lookup_symbol(last_tb->pc));
if (cc->synchronize_from_tb) {
cc->synchronize_from_tb(cpu, tb);
cc->synchronize_from_tb(cpu, last_tb);
} else {
assert(cc->set_pc);
cc->set_pc(cpu, tb->pc);
cc->set_pc(cpu, last_tb->pc);
}
}
if ((next_tb & TB_EXIT_MASK) == TB_EXIT_REQUESTED) {
if (tb_exit == TB_EXIT_REQUESTED) {
/* We were asked to stop executing TBs (probably a pending
* interrupt. We've now stopped, so clear the flag.
*/
cpu->tcg_exit_req = 0;
}
return next_tb;
return ret;
}
#ifndef CONFIG_USER_ONLY
@ -358,8 +361,8 @@ int cpu_exec(CPUState *cpu)
CPUArchState *env = &x86_cpu->env;
#endif
int ret, interrupt_request;
TranslationBlock *tb;
uintptr_t next_tb;
TranslationBlock *tb, *last_tb;
int tb_exit = 0;
SyncClocks sc;
/* replay_interrupt may need current_cpu */
@ -442,7 +445,7 @@ int cpu_exec(CPUState *cpu)
#endif
}
next_tb = 0; /* force lookup of first TB */
last_tb = NULL; /* forget the last executed TB after exception */
for(;;) {
interrupt_request = cpu->interrupt_request;
if (unlikely(interrupt_request)) {
@ -487,7 +490,7 @@ int cpu_exec(CPUState *cpu)
else {
replay_interrupt();
if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
next_tb = 0;
last_tb = NULL;
}
}
/* Don't use the cached interrupt_request value,
@ -496,7 +499,7 @@ int cpu_exec(CPUState *cpu)
cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
/* ensure that no TB jump will be modified as
the program flow was changed */
next_tb = 0;
last_tb = NULL;
}
}
if (unlikely(cpu->exit_request
@ -513,22 +516,24 @@ int cpu_exec(CPUState *cpu)
/* as some TB could have been invalidated because
of memory exceptions while generating the code, we
must recompute the hash index here */
next_tb = 0;
last_tb = NULL;
tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
}
/* See if we can patch the calling TB. */
if (next_tb != 0 && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
tb_add_jump((TranslationBlock *)(next_tb & ~TB_EXIT_MASK),
next_tb & TB_EXIT_MASK, tb);
if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
tb_add_jump(last_tb, tb_exit, tb);
}
tb_unlock();
if (likely(!cpu->exit_request)) {
uintptr_t ret;
trace_exec_tb(tb, tb->pc);
/* execute the generated code */
cpu->current_tb = tb;
next_tb = cpu_tb_exec(cpu, tb);
ret = cpu_tb_exec(cpu, tb);
cpu->current_tb = NULL;
switch (next_tb & TB_EXIT_MASK) {
last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
tb_exit = ret & TB_EXIT_MASK;
switch (tb_exit) {
case TB_EXIT_REQUESTED:
/* Something asked us to stop executing
* chained TBs; just continue round the main
@ -541,7 +546,7 @@ int cpu_exec(CPUState *cpu)
* or cpu->interrupt_request.
*/
smp_rmb();
next_tb = 0;
last_tb = NULL;
break;
case TB_EXIT_ICOUNT_EXPIRED:
{
@ -559,12 +564,12 @@ int cpu_exec(CPUState *cpu)
} else {
if (insns_left > 0) {
/* Execute remaining instructions. */
tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
cpu_exec_nocache(cpu, insns_left, tb, false);
cpu_exec_nocache(cpu, insns_left,
last_tb, false);
align_clocks(&sc, cpu);
}
cpu->exception_index = EXCP_INTERRUPT;
next_tb = 0;
last_tb = NULL;
cpu_loop_exit(cpu);
}
break;

19
tcg/tcg.h
View File

@ -925,7 +925,7 @@ static inline unsigned get_mmuidx(TCGMemOpIdx oi)
/**
* tcg_qemu_tb_exec:
* @env: CPUArchState * for the CPU
* @env: pointer to CPUArchState for the CPU
* @tb_ptr: address of generated code for the TB to execute
*
* Start executing code from a given translation block.
@ -936,30 +936,31 @@ static inline unsigned get_mmuidx(TCGMemOpIdx oi)
* which has not yet been directly linked, or an asynchronous
* event such as an interrupt needs handling.
*
* The return value is a pointer to the next TB to execute
* (if known; otherwise zero). This pointer is assumed to be
* 4-aligned, and the bottom two bits are used to return further
* information:
* Return: The return value is the value passed to the corresponding
* tcg_gen_exit_tb() at translation time of the last TB attempted to execute.
* The value is either zero or a 4-byte aligned pointer to that TB combined
* with additional information in its two least significant bits. The
* additional information is encoded as follows:
* 0, 1: the link between this TB and the next is via the specified
* TB index (0 or 1). That is, we left the TB via (the equivalent
* of) "goto_tb <index>". The main loop uses this to determine
* how to link the TB just executed to the next.
* 2: we are using instruction counting code generation, and we
* did not start executing this TB because the instruction counter
* would hit zero midway through it. In this case the next-TB pointer
* would hit zero midway through it. In this case the pointer
* returned is the TB we were about to execute, and the caller must
* arrange to execute the remaining count of instructions.
* 3: we stopped because the CPU's exit_request flag was set
* (usually meaning that there is an interrupt that needs to be
* handled). The next-TB pointer returned is the TB we were
* about to execute when we noticed the pending exit request.
* handled). The pointer returned is the TB we were about to execute
* when we noticed the pending exit request.
*
* If the bottom two bits indicate an exit-via-index then the CPU
* state is correctly synchronised and ready for execution of the next
* TB (and in particular the guest PC is the address to execute next).
* Otherwise, we gave up on execution of this TB before it started, and
* the caller must fix up the CPU state by calling the CPU's
* synchronize_from_tb() method with the next-TB pointer we return (falling
* synchronize_from_tb() method with the TB pointer we return (falling
* back to calling the CPU's set_pc method with tb->pb if no
* synchronize_from_tb() method exists).
*

6
tci.c
View File

@ -467,7 +467,7 @@ uintptr_t tcg_qemu_tb_exec(CPUArchState *env, uint8_t *tb_ptr)
{
long tcg_temps[CPU_TEMP_BUF_NLONGS];
uintptr_t sp_value = (uintptr_t)(tcg_temps + CPU_TEMP_BUF_NLONGS);
uintptr_t next_tb = 0;
uintptr_t ret = 0;
tci_reg[TCG_AREG0] = (tcg_target_ulong)env;
tci_reg[TCG_REG_CALL_STACK] = sp_value;
@ -1085,7 +1085,7 @@ uintptr_t tcg_qemu_tb_exec(CPUArchState *env, uint8_t *tb_ptr)
/* QEMU specific operations. */
case INDEX_op_exit_tb:
next_tb = *(uint64_t *)tb_ptr;
ret = *(uint64_t *)tb_ptr;
goto exit;
break;
case INDEX_op_goto_tb:
@ -1243,5 +1243,5 @@ uintptr_t tcg_qemu_tb_exec(CPUArchState *env, uint8_t *tb_ptr)
tci_assert(tb_ptr == old_code_ptr + op_size);
}
exit:
return next_tb;
return ret;
}

2
trace-events
View File

@ -1614,7 +1614,7 @@ kvm_failed_spr_get(int str, const char *msg) "Warning: Unable to retrieve SPR %d
# cpu-exec.c
disable exec_tb(void *tb, uintptr_t pc) "tb:%p pc=0x%"PRIxPTR
disable exec_tb_nocache(void *tb, uintptr_t pc) "tb:%p pc=0x%"PRIxPTR
disable exec_tb_exit(void *next_tb, unsigned int flags) "tb:%p flags=%x"
disable exec_tb_exit(void *last_tb, unsigned int flags) "tb:%p flags=%x"
# translate-all.c
translate_block(void *tb, uintptr_t pc, uint8_t *tb_code) "tb:%p, pc:0x%"PRIxPTR", tb_code:%p"