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include/exec/exec-all: document common exit conditions 

As a precursor to later patches attempt to come up with a more
concrete wording for what each of the common exit cases would be.

CC: Emilio G. Cota <cota@braap.org>
CC: Richard Henderson <rth@twiddle.net>
CC: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Message-id: 20170713141928.25419-2-alex.bennee@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Alex Bennée 2017-07-17 13:36:07 +01:00 committed by Peter Maydell
parent 8d92e26b45
commit df0311e634
1 changed files with 26 additions and 3 deletions
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29
include/exec/exec-all.h
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@ -35,11 +35,34 @@ typedef abi_ulong tb_page_addr_t;
typedef ram_addr_t tb_page_addr_t;
#endif
/* is_jmp field values */
/* DisasContext is_jmp field values
*
* is_jmp starts as DISAS_NEXT. The translator will keep processing
* instructions until an exit condition is reached. If we reach the
* exit condition and is_jmp is still DISAS_NEXT (because of some
* other condition) we simply "jump" to the next address.
* The remaining exit cases are:
*
* DISAS_JUMP - Only the PC was modified dynamically (e.g computed)
* DISAS_TB_JUMP - Only the PC was modified statically (e.g. branch)
*
* In these cases as long as the PC is updated we can chain to the
* next TB either by exiting the loop or looking up the next TB via
* the loookup helper.
*
* DISAS_UPDATE - CPU State was modified dynamically
*
* This covers any other CPU state which necessities us exiting the
* TCG code to the main run-loop. Typically this includes anything
* that might change the interrupt state.
*
* Individual translators may define additional exit cases to deal
* with per-target special conditions.
*/
#define DISAS_NEXT 0 /* next instruction can be analyzed */
#define DISAS_JUMP 1 /* only pc was modified dynamically */
#define DISAS_UPDATE 2 /* cpu state was modified dynamically */
#define DISAS_TB_JUMP 3 /* only pc was modified statically */
#define DISAS_TB_JUMP 2 /* only pc was modified statically */
#define DISAS_UPDATE 3 /* cpu state was modified dynamically */
#include "qemu/log.h"