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tcg: Implement implicit ordering semantics 

Currently, we cannot use mttcg for running strong memory model guests
on weak memory model hosts due to missing ordering semantics.

We implicitly generate fence instructions for stronger guests if an
ordering mismatch is detected. We generate fences only for the orders
for which fence instructions are necessary, for example a fence is not
necessary between a store and a subsequent load on x86 since its
absence in the guest binary tells that ordering need not be
ensured. Also note that if we find multiple subsequent fence
instructions in the generated IR, we combine them in the TCG
optimization pass.

This patch allows us to boot an x86 guest on ARM64 hosts using mttcg.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Message-Id: <20170829063313.10237-4-bobby.prani@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Pranith Kumar 2017-08-29 02:33:12 -04:00 committed by Richard Henderson
parent 71650df7b0
commit b32dc3370a
1 changed files with 16 additions and 0 deletions
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16
tcg/tcg-op.c
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@ -28,6 +28,7 @@
#include "exec/exec-all.h"
#include "tcg.h"
#include "tcg-op.h"
#include "tcg-mo.h"
#include "trace-tcg.h"
#include "trace/mem.h"
@ -2662,8 +2663,20 @@ static void gen_ldst_i64(TCGOpcode opc, TCGv_i64 val, TCGv addr,
#endif
}
static void tcg_gen_req_mo(TCGBar type)
{
#ifdef TCG_GUEST_DEFAULT_MO
type &= TCG_GUEST_DEFAULT_MO;
#endif
type &= ~TCG_TARGET_DEFAULT_MO;
if (type) {
tcg_gen_mb(type | TCG_BAR_SC);
}
}
void tcg_gen_qemu_ld_i32(TCGv_i32 val, TCGv addr, TCGArg idx, TCGMemOp memop)
{
tcg_gen_req_mo(TCG_MO_LD_LD | TCG_MO_ST_LD);
memop = tcg_canonicalize_memop(memop, 0, 0);
trace_guest_mem_before_tcg(tcg_ctx.cpu, tcg_ctx.tcg_env,
addr, trace_mem_get_info(memop, 0));
@ -2672,6 +2685,7 @@ void tcg_gen_qemu_ld_i32(TCGv_i32 val, TCGv addr, TCGArg idx, TCGMemOp memop)
void tcg_gen_qemu_st_i32(TCGv_i32 val, TCGv addr, TCGArg idx, TCGMemOp memop)
{
tcg_gen_req_mo(TCG_MO_LD_ST | TCG_MO_ST_ST);
memop = tcg_canonicalize_memop(memop, 0, 1);
trace_guest_mem_before_tcg(tcg_ctx.cpu, tcg_ctx.tcg_env,
addr, trace_mem_get_info(memop, 1));
@ -2680,6 +2694,7 @@ void tcg_gen_qemu_st_i32(TCGv_i32 val, TCGv addr, TCGArg idx, TCGMemOp memop)
void tcg_gen_qemu_ld_i64(TCGv_i64 val, TCGv addr, TCGArg idx, TCGMemOp memop)
{
tcg_gen_req_mo(TCG_MO_LD_LD | TCG_MO_ST_LD);
if (TCG_TARGET_REG_BITS == 32 && (memop & MO_SIZE) < MO_64) {
tcg_gen_qemu_ld_i32(TCGV_LOW(val), addr, idx, memop);
if (memop & MO_SIGN) {
@ -2698,6 +2713,7 @@ void tcg_gen_qemu_ld_i64(TCGv_i64 val, TCGv addr, TCGArg idx, TCGMemOp memop)
void tcg_gen_qemu_st_i64(TCGv_i64 val, TCGv addr, TCGArg idx, TCGMemOp memop)
{
tcg_gen_req_mo(TCG_MO_LD_ST | TCG_MO_ST_ST);
if (TCG_TARGET_REG_BITS == 32 && (memop & MO_SIZE) < MO_64) {
tcg_gen_qemu_st_i32(TCGV_LOW(val), addr, idx, memop);
return;