tcg: add perfmap and jitdump

Add ability to dump /tmp/perf-<pid>.map and jit-<pid>.dump.
The first one allows the perf tool to map samples to each individual
translation block. The second one adds the ability to resolve symbol
names, line numbers and inspect JITed code.

Example of use:

    perf record qemu-x86_64 -perfmap ./a.out
    perf report

or

    perf record -k 1 qemu-x86_64 -jitdump ./a.out
    DEBUGINFOD_URLS= perf inject -j -i perf.data -o perf.data.jitted
    perf report -i perf.data.jitted

Co-developed-by: Vanderson M. do Rosario <vandersonmr2@gmail.com>
Co-developed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230112152013.125680-4-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

docs/devel/tcg.rst

@@ -188,3 +188,26 @@ memory areas instead calls out to C code for device emulation.
 Finally, the MMU helps tracking dirty pages and pages pointed to by
 translation blocks.
 
+Profiling JITted code
+---------------------
+
+The Linux ``perf`` tool will treat all JITted code as a single block as
+unlike the main code it can't use debug information to link individual
+program counter samples with larger functions. To overcome this
+limitation you can use the ``-perfmap`` or the ``-jitdump`` option to generate
+map files. ``-perfmap`` is lightweight and produces only guest-host mappings.
+``-jitdump`` additionally saves JITed code and guest debug information (if
+available); its output needs to be integrated with the ``perf.data`` file
+before the final report can be viewed.
+
+.. code::
+
+  perf record $QEMU -perfmap $REMAINING_ARGS
+  perf report
+
+  perf record -k 1 $QEMU -jitdump $REMAINING_ARGS
+  DEBUGINFOD_URLS= perf inject -j -i perf.data -o perf.data.jitted
+  perf report -i perf.data.jitted
+
+Note that qemu-system generates mappings only for ``-kernel`` files in ELF
+format.