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tcg arm/mips/ia64: add a comment about retranslation and caches

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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 <edgar.iglesias@gmail.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Aurelien Jarno 2011-01-10 18:30:05 +01:00
parent dace20dcc9
commit 5677903453
3 changed files with 9 additions and 1 deletions
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3
tcg/arm/tcg-target.c
View File

@ -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) 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 #ifdef HOST_WORDS_BIGENDIAN
tcg_out8(s, (cond << 4) | 0x0a); tcg_out8(s, (cond << 4) | 0x0a);
s->code_ptr += 3; s->code_ptr += 3;

3
tcg/ia64/tcg-target.c
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@ -871,6 +871,9 @@ static void tcg_out_br(TCGContext *s, int label_index)
{ {
TCGLabel *l = &s->labels[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_out_bundle(s, mmB,
tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0), tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0),
tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0), tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0),

4
tcg/mips/tcg-target.c
View File

@ -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) 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); uint16_t offset = (uint16_t)(*(uint32_t *) s->code_ptr);
tcg_out_opc_imm(s, opc, rt, rs, offset); tcg_out_opc_imm(s, opc, rt, rs, offset);