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This document details how the Android-specific -trace <name> instruction works.
hw/goldfish_trace.c:
- virtual hardware i/o memory used by the goldfish kernel to send event information
to the emulator (e.g. context switches, forks, execs, etc...). Used by both -trace
and -memcheck implementations.
trace.c/trace.h:
- support functions for the runtime tracing facility. E.g. record static/dynamic
blocks, compute instruction sizes, etc..
trace_common.h:
- a header included by "trace.h" but also by the sources of the trace file processor
tool (sdk/emulator/qtools). Defines common data structures and types only.
target-arm/translate.c:
- each new translated basic block is recorded by:
1. calling trace_bb_start()
2. for each instruction in the block, calling trace_bb_insn()
3. calling trace_bb_end() at the end of the basic block.
this is done at "translation time".
- each basic block is translated into a "tb" of x86 machine code that
will have, at its start, a call to a helper function like:
trace_bb_helper(bb_num, tb)
where 'bb_num' is the unique 64-bit ID of the original basic block.
-> at "execution time", we record which BB are executed.
- we record context switches and other events from goldfish_trace.c through
functions like trace_switch(), trace_fork(), trace_exception(), etc...
(see trace.c, some of these miss a declaration in trace.h)
- see genTraceTicks(), genTraceBB()
- the number of virtual CPU cycles / instruction is returned by get_insn_ticks_arm()
(implemented in trace.c). This does not account for dynamic data interlocks or
variable cycles due to operand sizes (e.g. multiplications instructions).
target-arm/helpers.h:
- contains a list of helper functions that are going to be called by x86 machine code
at runtime. see #ifdef CONFIG_TRACE .. #endif
target-arm/helpers.c:
- implementation of the helper functions. see #ifdef CONFIG_TRACE .. #endif at the end
- helper traceTicks(ticks): used to record that we executed 'ticks' simulated ARM CPU
cycles. This just increments a global uint64_t counter.
- helper traceInsn(): used to record that we executed properly a single instruction.
this allows to properly recover/profile when a basic block is exited by an exceptional
condition (e.g. a signal, a page fault, etc...), instead of reaching its end.
- helper_traceBB32/traceBB64: used to record that we entered a given basic block at
runtime. Simply calls trace_bb_helper()
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