On 2015-06-19 08:09, Pavel Dovgaluk wrote: > > From: Aurelien Jarno [mailto:aurel...@aurel32.net] > > On 2015-06-18 12:02, Paolo Bonzini wrote: > > > > > > TCG can then use them to fill in an array stored inside the > > > TranslationBlock, together with the host PC. Since the gen_opc_pc, > > > gen_opc_instr_start, gen_opc_icount arrays are inside tcg_ctx, it may be > > > a good idea to store the checkpoint information compressed in a byte > > > array (e.g. as a series of ULEB128 values---the host and target PCs can > > > even be stored as deltas from the last value). > > > > Either as deltas to the last value or as delta from the start of the > > TB. What I am worried about is the size of the checkpoint information, > > even if we do some compression, we might have one per guest instruction. > > I have implemented a naive version of that without compression, storing > > the checkpoint data at the end of the generated code, and it's about 30% > > of the size of the TB for MIPS. It's probably smaller on architectures > > storing only the PC. Also it's size is quite variable. That's why it's > > probably not a good idea to store it directly in the TranslationBlock. > > I don't like storing it directly in the generated code either, > > especially given this part is supposed to be executable. > > > > > As a first step, gen_intermediate_code_pc and tcg_gen_code_search_pc can > > > then be merged into a single target-independent function that > > > uncompresses the byte array up to the required host PC into tcg_ctx. > > > Later you can optimize them to remove the tcg_ctx arrays altogether. > > > > > > So the patches could be something like this: > > > > > > 1) SPARC: put the jump target information directly in gen_opc_* without > > > using gen_opc_jump_pc (not trivial) > > > > > > 2) a few targets: instead of gen_opc_* arrays, use a new generic member > > > of tcg_ctx (similar to how csbase is used generically), e.g. > > > tcg_ctx.gen_opc_target1[] and tcg_ctx.gen_opc_target2[]. > > > > > > 3) all targets: always fill in tcg_ctx.gen_*, even if search_pc is false > > > > > > 4) TCG: add support for a checkpoint operation, make it fill in > > > tcg_ctx.gen_* > > > > > > 5) all targets: change explicit filling of tcg_ctx.gen_* to use the > > > checkpoint operation > > > > > > 6) TCG/translate-all: convert gen_intermediate_code_pc as outlined above > > > > That's sounds like a plan when I have more time ;-) > > Doesn't this approach still require my fixes to work correctly?
Yes it does. Aurélien -- Aurelien Jarno GPG: 4096R/1DDD8C9B aurel...@aurel32.net http://www.aurel32.net
