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trace: [tcg] Add documentation

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Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Lluís Vilanova 2014-05-30 14:11:26 +02:00 committed by Stefan Hajnoczi
parent e0b2fd0efb
commit 0bb403b0ae
1 changed files with 40 additions and 0 deletions
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docs/tracing.txt
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@ -307,3 +307,43 @@ guard such computations and avoid its compilation when the event is disabled:
You can check both if the event has been disabled and is dynamically enabled at
the same time using the 'trace_event_get_state' routine (see header
"trace/control.h" for more information).
=== "tcg" ===
Guest code generated by TCG can be traced by defining an event with the "tcg"
event property. Internally, this property generates two events:
"<eventname>_trans" to trace the event at translation time, and
"<eventname>_exec" to trace the event at execution time.
Instead of using these two events, you should instead use the function
"trace_<eventname>_tcg" during translation (TCG code generation). This function
will automatically call "trace_<eventname>_trans", and will generate the
necessary TCG code to call "trace_<eventname>_exec" during guest code execution.
Events with the "tcg" property can be declared in the "trace-events" file with a
mix of native and TCG types, and "trace_<eventname>_tcg" will gracefully forward
them to the "<eventname>_trans" and "<eventname>_exec" events. Since TCG values
are not known at translation time, these are ignored by the "<eventname>_trans"
event. Because of this, the entry in the "trace-events" file needs two printing
formats (separated by a comma):
tcg foo(uint8_t a1, TCGv_i32 a2) "a1=%d", "a1=%d a2=%d"
For example:
#include "trace-tcg.h"
void some_disassembly_func (...)
{
uint8_t a1 = ...;
TCGv_i32 a2 = ...;
trace_foo_tcg(a1, a2);
}
This will immediately call:
void trace_foo_trans(uint8_t a1);
and will generate the TCG code to call:
void trace_foo(uint8_t a1, uint32_t a2);