[Qemu-devel] [PATCH v2 0/3] tcg: Support debugging leakage of temporaries

[Peter Maydell]

This patchset removes the ad-hoc debug code in target-arm for
identifying cases where we leaked TCG temporary variables, in
favour of an implementation in tcg itself.

Generally any temporaries created by a target while it is
translating an instruction should be freed by the end of that
instruction; otherwise carefully crafted guest code could cause
TCG to run out of temporaries and assert.

Putting the leak-debugging code into TCG proper (a) makes more
sense as this isn't at all arm-specific (b) makes it more
comprehensive, as it now covers temporaries created in all ways,
not just via the new_tmp()/dead_tmp() wrapper functions
(c) avoids annoying false positives where eg a TCG temp created
with tcg_const_i32() was passed to dead_tmp().

The tracking only happens if qemu was configured with
--enable-debug-tcg. It should be easy to add to other targets if
desired; it's just a matter of calling tcg_clear_temp_count()
and tcg_check_temp_count() in the appropriate places.

Changes since v1:
 use "do { } while (0)" for the non-debug version of the
 tcg_clear_temp_count() macro to avoid creating empty statements

Peter Maydell (3):
  tcg: Add support for debugging leakage of temporaries
  target-arm: Remove ad-hoc leak checking code
  target-arm: Use TCG temporary leak debugging facilities

 target-arm/translate.c |  705 +++++++++++++++++++++++------------------------
 tcg/tcg.c              |   32 +++
 tcg/tcg.h              |   17 ++
 3 files changed, 394 insertions(+), 360 deletions(-)