From 99d8a00235e58d5f0b65abafcfcf839984225a92 Mon Sep 17 00:00:00 2001 From: Aurelien Jarno Date: Mon, 10 Jan 2011 18:30:05 +0100 Subject: [PATCH] tcg arm/mips/ia64: add a comment about retranslation and caches Add a comment about cache coherency and retranslation, so that people developping new targets based on existing ones are warned of the issue. Acked-by: Edgar E. Iglesias Signed-off-by: Aurelien Jarno --- tcg/arm/tcg-target.c | 3 +++ tcg/ia64/tcg-target.c | 3 +++ tcg/mips/tcg-target.c | 4 +++- 3 files changed, 9 insertions(+), 1 deletion(-) diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c index 1eb5605..918e2f7 100644 --- a/tcg/arm/tcg-target.c +++ b/tcg/arm/tcg-target.c @@ -352,6 +352,9 @@ static inline void tcg_out_b(TCGContext *s, int cond, int32_t offset) static inline void tcg_out_b_noaddr(TCGContext *s, int cond) { + /* We pay attention here to not modify the branch target by skipping + the corresponding bytes. This ensure that caches and memory are + kept coherent during retranslation. */ #ifdef HOST_WORDS_BIGENDIAN tcg_out8(s, (cond << 4) | 0x0a); s->code_ptr += 3; diff --git a/tcg/ia64/tcg-target.c b/tcg/ia64/tcg-target.c index e2e44f7..8dac7f7 100644 --- a/tcg/ia64/tcg-target.c +++ b/tcg/ia64/tcg-target.c @@ -871,6 +871,9 @@ static void tcg_out_br(TCGContext *s, int label_index) { TCGLabel *l = &s->labels[label_index]; + /* We pay attention here to not modify the branch target by reading + the existing value and using it again. This ensure that caches and + memory are kept coherent during retranslation. */ tcg_out_bundle(s, mmB, tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0), tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0), diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c index 4e92a50..e04b0dc 100644 --- a/tcg/mips/tcg-target.c +++ b/tcg/mips/tcg-target.c @@ -351,7 +351,9 @@ static inline void tcg_out_opc_imm(TCGContext *s, int opc, int rt, int rs, int i */ static inline void tcg_out_opc_br(TCGContext *s, int opc, int rt, int rs) { - /* We need to keep the offset unchanged for retranslation */ + /* We pay attention here to not modify the branch target by reading + the existing value and using it again. This ensure that caches and + memory are kept coherent during retranslation. */ uint16_t offset = (uint16_t)(*(uint32_t *) s->code_ptr); tcg_out_opc_imm(s, opc, rt, rs, offset); -- 2.7.4