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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.

Backports commit 819af24b9c1e95e6576f1cefd32f4d6bf56dfa56 from qemu
This commit is contained in:
Sergey Fedorov 2018-02-23 23:26:53 -05:00 committed by Lioncash
parent 66faf3b5df
commit c9700af2bd
No known key found for this signature in database
GPG key ID: 4E3C3CC1031BA9C7
2 changed files with 43 additions and 36 deletions
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60
qemu/cpu-exec.c
View file

@ -44,11 +44,10 @@ int cpu_exec(struct uc_struct *uc, CPUState *cpu)
X86CPU *x86_cpu = X86_CPU(uc, cpu);
#endif
int ret, interrupt_request;
TranslationBlock *tb;
uintptr_t next_tb;
TranslationBlock *tb, *last_tb;
int tb_exit = 0;
struct hook *hook;
if (cpu->halted) {
if (!cpu_has_work(cpu)) {
return EXCP_HALTED;
@ -130,7 +129,7 @@ int cpu_exec(struct uc_struct *uc, CPUState *cpu)
}
}
next_tb = 0; /* force lookup of first TB */
last_tb = NULL; /* forget the last executed TB after exception */
for(;;) {
interrupt_request = cpu->interrupt_request;
@ -167,7 +166,7 @@ int cpu_exec(struct uc_struct *uc, CPUState *cpu)
True when it is, and we should restart on a new TB,
and via longjmp via cpu_loop_exit. */
if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
next_tb = 0;
last_tb = NULL;
}
/* Don't use the cached interrupt_request value,
do_interrupt may have updated the EXITTB flag. */
@ -175,7 +174,7 @@ int cpu_exec(struct uc_struct *uc, 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)) {
@ -195,22 +194,23 @@ int cpu_exec(struct uc_struct *uc, 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);
}
if (likely(!cpu->exit_request)) {
uintptr_t ret;
cpu->current_tb = tb;
/* execute the generated code */
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
@ -223,8 +223,7 @@ int cpu_exec(struct uc_struct *uc, CPUState *cpu)
* or cpu->interrupt_request.
*/
smp_rmb();
tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
next_tb = 0;
last_tb = NULL;
break;
default:
break;
@ -277,46 +276,53 @@ static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
{
CPUArchState *env = cpu->env_ptr;
TCGContext *tcg_ctx = env->uc->tcg_ctx;
uintptr_t next_tb;
uintptr_t ret;
TranslationBlock *last_tb;
int tb_exit;
uint8_t *tb_ptr = itb->tc_ptr;
// Unicorn: commented out
//qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
// "Trace %p [" TARGET_FMT_lx "] %s\n",
// itb->tc_ptr, itb->pc, lookup_symbol(itb->pc));
next_tb = tcg_qemu_tb_exec(env, tb_ptr);
ret = tcg_qemu_tb_exec(env, tb_ptr);
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(env->uc, cpu);
TranslationBlock *tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
// Unicorn: commented out
//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) {
// avoid sync twice when helper_uc_tracecode() already did this.
if (env->uc->emu_counter <= env->uc->emu_count &&
!env->uc->stop_request && !env->uc->quit_request)
cc->synchronize_from_tb(cpu, tb);
!env->uc->stop_request && !env->uc->quit_request) {
cc->synchronize_from_tb(cpu, last_tb);
}
} else {
assert(cc->set_pc);
// avoid sync twice when helper_uc_tracecode() already did this.
if (env->uc->emu_counter <= env->uc->emu_count && !env->uc->quit_request)
cc->set_pc(cpu, tb->pc);
if (env->uc->emu_counter <= env->uc->emu_count && !env->uc->quit_request) {
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;
}
static TranslationBlock *tb_find_slow(CPUState *cpu,

19
qemu/tcg/tcg.h
View file

@ -1062,7 +1062,7 @@ 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.
@ -1073,22 +1073,23 @@ 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
* handled). The pointer returned is the TB we were about to execute
* when we noticed the pending exit request.
* about to execute when we noticed the pending exit request.
*
* If the bottom two bits indicate an exit-via-index then the CPU
@ -1096,7 +1097,7 @@ static inline unsigned get_mmuidx(TCGMemOpIdx oi)
* 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).
*