On Mon, Jan 10, 2011 at 06:34:42PM +0100, Aurelien Jarno wrote:
> Add a comment about cache coherency and retranslation, so that people
> developping new targets based on existing ones are warned of the issue.
>
> Cc: Alexander Graf <ag...@suse.de>
> Cc: Edgar E. Iglesias <edgar.igles...@gmail.com>
> Signed-off-by: Aurelien Jarno <aurel...@aurel32.net>
Looks good to me, thanks.
Acked-by: Edgar E. Iglesias <edgar.igles...@gmail.com>
> ---
> tcg/arm/tcg-target.c | 3 +++
> tcg/ia64/tcg-target.c | 3 +++
> tcg/mips/tcg-target.c | 4 +++-
> 3 files changed, 9 insertions(+), 1 deletions(-)
>
> 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);
> --
> 1.7.2.3
>
