Add output of cbrtrace.c to support branch entropy calculation. #6278
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derekbruening
requested changes
Aug 28, 2023
| /* Clean call for the cbr */ | ||
| static void | ||
| at_cbr(app_pc inst_addr, app_pc targ_addr, app_pc fall_addr, int taken, void *bb_addr) | ||
| { | ||
| cbrn += 1; |
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This global variable increment is racy and will be inaccurate for many-threaded apps. Best to use thread-local counters and aggregate at thread exit time under a lock (see e.g. instrace_simple num_refs).
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| static client_id_t client_id; | ||
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| static int tls_idx; | ||
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| static long cbrn = 0; |
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I have never seen "n" as a suffix -- best to use a clearer name like "cbr_count".
| @@ -93,6 +98,8 @@ event_thread_exit(void *drcontext) | |||
| static void | |||
| event_exit(void) | |||
| { | |||
| dr_fprintf(STDERR, "CBR instruction number: %ld, taken: %ld, not taken: %ld\n", cbrn, | |||
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This needs to be inside SHOW_RESULTS to allow a build with no output.
| @@ -75,10 +80,10 @@ event_thread_init(void *drcontext) | |||
| { | |||
| file_t log; | |||
| log = | |||
| log_file_open(client_id, drcontext, NULL /* using client lib path */, "cbrtrace", | |||
| log_file_open(client_id, drcontext, NULL /* using client lib path */, "cbrtrace", | |||
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Please maintain the clang-format style. This is likely why all the tests are failing.
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Add the output of CBR instruction number, taken number, and not taken number on the console before the information of "Client 'cbrtrace' exiting,", like this:
CBR instruction number: 826871, taken: 432406, not taken: 394465
Client 'cbrtrace' exiting
Instead of printing all the branch information, a commonly used metric to evaluate branch behavior is branch entropy. Branch entropy is calculated based on the taken ratio of CBR instructions