The following code shows how to organize debug printing with minimal impact on the loaded system
#include <syslog.h>
#include <stdarg.h>
#include <stdlib.h>
static void print_at(const char *srcfile, int line, const char *format, ...) {
va_list ap;
const char *envvar="JAVA_SHOULD_PRINT_AT";
static int requested_line = -1;
if (requested_line == -1) {
const char *should_print = getenv(envvar);
requested_line = (should_print != NULL) ? atoi(should_print) : 0;
openlog("javadebug", LOG_PID, LOG_UUCP);
}
if (requested_line == line) {
va_start(ap, format);
vsyslog(LOG_DEBUG, format, ap);
va_end(ap);
}
}
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It's not always obvious what assembly will be generated after expanding all the macros of the HotSpot meta-assembly system. The following code shows how to print the actual code generated by HotSpot.
// #define DMS_DEBUG
#ifdef DMS_DEBUG
address barrier_start = masm->code()->insts_end();
#endif
__ block_comment("nmethod_barrier begin");
__ ldr_label(tmp0, guard);
...
__ bind(skip);
__ block_comment("nmethod_barrier end");
#ifdef DMS_DEBUG
address barrier_end = masm->code()->insts_end();
tty->print_cr("DMS: barier %p %p bytes: %d", barrier_start, barrier_end, barrier_end - barrier_start);
// masm->code()->print();
masm->code()->decode();
#endif
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