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target/ppc: Emulate LL/SC using cmpxchg helpers 

Emulating LL/SC with cmpxchg is not correct, since it can suffer from
the ABA problem. However, portable parallel code is written assuming
only cmpxchg which means that in practice this is a viable alternative.

Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Nikunj A Dadhania 2017-04-27 10:48:19 +05:30 committed by David Gibson
parent a1a636b8b4
commit 253ce7b2cf
1 changed files with 23 additions and 6 deletions
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29
target/ppc/translate.c
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@ -73,6 +73,7 @@ static TCGv cpu_cfar;
#endif
static TCGv cpu_xer, cpu_so, cpu_ov, cpu_ca, cpu_ov32, cpu_ca32;
static TCGv cpu_reserve;
static TCGv cpu_reserve_val;
static TCGv cpu_fpscr;
static TCGv_i32 cpu_access_type;
@ -181,6 +182,9 @@ void ppc_translate_init(void)
cpu_reserve = tcg_global_mem_new(cpu_env,
offsetof(CPUPPCState, reserve_addr),
"reserve_addr");
cpu_reserve_val = tcg_global_mem_new(cpu_env,
offsetof(CPUPPCState, reserve_val),
"reserve_val");
cpu_fpscr = tcg_global_mem_new(cpu_env,
offsetof(CPUPPCState, fpscr), "fpscr");
@ -3023,7 +3027,7 @@ static void gen_##name(DisasContext *ctx) \
} \
tcg_gen_qemu_ld_tl(gpr, t0, ctx->mem_idx, memop); \
tcg_gen_mov_tl(cpu_reserve, t0); \
tcg_gen_st_tl(gpr, cpu_env, offsetof(CPUPPCState, reserve_val)); \
tcg_gen_mov_tl(cpu_reserve_val, gpr); \
tcg_temp_free(t0); \
}
@ -3155,14 +3159,27 @@ static void gen_conditional_store(DisasContext *ctx, TCGv EA,
static void gen_conditional_store(DisasContext *ctx, TCGv EA,
int reg, int memop)
{
TCGLabel *l1;
TCGLabel *l1 = gen_new_label();
TCGLabel *l2 = gen_new_label();
TCGv t0;
tcg_gen_trunc_tl_i32(cpu_crf[0], cpu_so);
l1 = gen_new_label();
tcg_gen_brcond_tl(TCG_COND_NE, EA, cpu_reserve, l1);
tcg_gen_ori_i32(cpu_crf[0], cpu_crf[0], CRF_EQ);
tcg_gen_qemu_st_tl(cpu_gpr[reg], EA, ctx->mem_idx, memop);
t0 = tcg_temp_new();
tcg_gen_atomic_cmpxchg_tl(t0, cpu_reserve, cpu_reserve_val,
cpu_gpr[reg], ctx->mem_idx,
DEF_MEMOP(memop) | MO_ALIGN);
tcg_gen_setcond_tl(TCG_COND_EQ, t0, t0, cpu_reserve_val);
tcg_gen_shli_tl(t0, t0, CRF_EQ_BIT);
tcg_gen_or_tl(t0, t0, cpu_so);
tcg_gen_trunc_tl_i32(cpu_crf[0], t0);
tcg_temp_free(t0);
tcg_gen_br(l2);
gen_set_label(l1);
tcg_gen_trunc_tl_i32(cpu_crf[0], cpu_so);
gen_set_label(l2);
tcg_gen_movi_tl(cpu_reserve, -1);
}
#endif