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tcg: Emit prologue to the beginning of code_gen_buffer

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By putting the prologue at the end, we risk overwriting the
prologue should our estimate of maximum TB size.  Given the
two different placements of the call to tcg_prologue_init,
move the high water mark computation into tcg_prologue_init.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Richard Henderson 2015-09-18 23:43:05 -07:00
parent 04fe640001
commit 8163b74938
2 changed files with 35 additions and 24 deletions
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35
tcg/tcg.c
View File

@ -363,17 +363,38 @@ void tcg_context_init(TCGContext *s)
void tcg_prologue_init(TCGContext *s)
{
/* init global prologue and epilogue */
s->code_buf = s->code_gen_prologue;
s->code_ptr = s->code_buf;
size_t prologue_size, total_size;
void *buf0, *buf1;
/* Put the prologue at the beginning of code_gen_buffer. */
buf0 = s->code_gen_buffer;
s->code_ptr = buf0;
s->code_buf = buf0;
s->code_gen_prologue = buf0;
/* Generate the prologue. */
tcg_target_qemu_prologue(s);
flush_icache_range((uintptr_t)s->code_buf, (uintptr_t)s->code_ptr);
buf1 = s->code_ptr;
flush_icache_range((uintptr_t)buf0, (uintptr_t)buf1);
/* Deduct the prologue from the buffer. */
prologue_size = tcg_current_code_size(s);
s->code_gen_ptr = buf1;
s->code_gen_buffer = buf1;
s->code_buf = buf1;
total_size = s->code_gen_buffer_size - prologue_size;
s->code_gen_buffer_size = total_size;
/* Compute a high-water mark, at which we voluntarily flush the
buffer and start over. */
s->code_gen_buffer_max_size = total_size - TCG_MAX_OP_SIZE * OPC_BUF_SIZE;
tcg_register_jit(s->code_gen_buffer, total_size);
#ifdef DEBUG_DISAS
if (qemu_loglevel_mask(CPU_LOG_TB_OUT_ASM)) {
size_t size = tcg_current_code_size(s);
qemu_log("PROLOGUE: [size=%zu]\n", size);
log_disas(s->code_buf, size);
qemu_log("PROLOGUE: [size=%zu]\n", prologue_size);
log_disas(buf0, prologue_size);
qemu_log("\n");
qemu_log_flush();
}

24
translate-all.c
View File

@ -690,23 +690,15 @@ static inline void code_gen_alloc(size_t tb_size)
}
qemu_madvise(tcg_ctx.code_gen_buffer, tcg_ctx.code_gen_buffer_size,
QEMU_MADV_HUGEPAGE);
QEMU_MADV_HUGEPAGE);
/* Steal room for the prologue at the end of the buffer. This ensures
(via the MAX_CODE_GEN_BUFFER_SIZE limits above) that direct branches
from TB's to the prologue are going to be in range. It also means
that we don't need to mark (additional) portions of the data segment
as executable. */
tcg_ctx.code_gen_prologue = tcg_ctx.code_gen_buffer +
tcg_ctx.code_gen_buffer_size - 1024;
tcg_ctx.code_gen_buffer_size -= 1024;
/* Estimate a good size for the number of TBs we can support. We
still haven't deducted the prologue from the buffer size here,
but that's minimal and won't affect the estimate much. */
tcg_ctx.code_gen_max_blocks
= tcg_ctx.code_gen_buffer_size / CODE_GEN_AVG_BLOCK_SIZE;
tcg_ctx.tb_ctx.tbs = g_new(TranslationBlock, tcg_ctx.code_gen_max_blocks);
tcg_ctx.code_gen_buffer_max_size = tcg_ctx.code_gen_buffer_size -
(TCG_MAX_OP_SIZE * OPC_BUF_SIZE);
tcg_ctx.code_gen_max_blocks = tcg_ctx.code_gen_buffer_size /
CODE_GEN_AVG_BLOCK_SIZE;
tcg_ctx.tb_ctx.tbs =
g_malloc(tcg_ctx.code_gen_max_blocks * sizeof(TranslationBlock));
qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock);
}
@ -717,8 +709,6 @@ void tcg_exec_init(unsigned long tb_size)
{
cpu_gen_init();
code_gen_alloc(tb_size);
tcg_ctx.code_gen_ptr = tcg_ctx.code_gen_buffer;
tcg_register_jit(tcg_ctx.code_gen_buffer, tcg_ctx.code_gen_buffer_size);
page_init();
#if defined(CONFIG_SOFTMMU)
/* There's no guest base to take into account, so go ahead and