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docs: remove references to TCG tracing

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Users wanting this sort of functionality should turn to TCG plugins
instead.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Cc: Luis Vilanova <vilanova@imperial.ac.uk>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220204204335.1689602-18-alex.bennee@linaro.org>
This commit is contained in:
Alex Bennée 2022-02-04 20:43:26 +00:00
parent 3bdc19af00
commit d9a6bad542
2 changed files with 13 additions and 85 deletions
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13
docs/about/removed-features.rst
View File

@ -601,6 +601,19 @@ the upstream Linux kernel in 2018, and it has also been dropped from glibc, so
there is no new Linux development taking place with this architecture. For
running the old binaries, you can use older versions of QEMU.
TCG introspection features
--------------------------
TCG trace-events (since 6.2)
''''''''''''''''''''''''''''
The ability to add new TCG trace points had bit rotted and as the
feature can be replicated with TCG plugins it was removed. If
any user is currently using this feature and needs help with
converting to using TCG plugins they should contact the qemu-devel
mailing list.
System emulator devices
-----------------------

85
docs/devel/tracing.rst
View File

@ -413,88 +413,3 @@ disabled, this check will have no performance impact.
return ptr;
}
"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);
"vcpu"
------
Identifies events that trace vCPU-specific information. It implicitly adds a
"CPUState*" argument, and extends the tracing print format to show the vCPU
information. If used together with the "tcg" property, it adds a second
"TCGv_env" argument that must point to the per-target global TCG register that
points to the vCPU when guest code is executed (usually the "cpu_env" variable).
The "tcg" and "vcpu" properties are currently only honored in the root
./trace-events file.
The following example events::
foo(uint32_t a) "a=%x"
vcpu bar(uint32_t a) "a=%x"
tcg vcpu baz(uint32_t a) "a=%x", "a=%x"
Can be used as::
#include "trace-tcg.h"
CPUArchState *env;
TCGv_ptr cpu_env;
void some_disassembly_func(...)
{
/* trace emitted at this point */
trace_foo(0xd1);
/* trace emitted at this point */
trace_bar(env_cpu(env), 0xd2);
/* trace emitted at this point (env) and when guest code is executed (cpu_env) */
trace_baz_tcg(env_cpu(env), cpu_env, 0xd3);
}
If the translating vCPU has address 0xc1 and code is later executed by vCPU
0xc2, this would be an example output::
// at guest code translation
foo a=0xd1
bar cpu=0xc1 a=0xd2
baz_trans cpu=0xc1 a=0xd3
// at guest code execution
baz_exec cpu=0xc2 a=0xd3