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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 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 the same time using the 'trace_event_get_state' routine (see header
"trace/control.h" for more information). "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);