The use of a pointer (not access, only for computations) after its
deallocation is forbiden in ISO C, but seems to work fine in all
platforms we are aware of. So, using that to correct stack pointers
after a stack reallocation seems safe and is much simpler than the
current implementation (first change all pointers to offsets and
then changing the offsets back to pointers). Anyway, for now that
option is disabled.
That reduces the size of "CallInfo". Moreover, bit CIST_HOOKED from
call status is not needed. When in a hook, 'transferinfo' is always
valid, being zero when the hook is not call/return.
Therefore, fields ftransfer/ntransfer in lua_Debug must have type
'int'. (Maximum stack size must fit in an 'int'.) Also, this commit
adds check that maximum stack size respects size_t for size in bytes.
Several definitions that don't need to be "global" (that is, that
concerns only specific parts of the code) moved out of llimits.h,
to more appropriate places.
Yielding in a hook must decrease the program counter, because it already
counted an instruction that, in the end, was not executed. However,
that decrement should be done only when about to restart the thread.
Otherwise, inspecting the thread with the debug library shows it one
instruction behind of where it really is.
To avoid the need of both the old and the new stack addresses valid
at the same time, to correct the pointers to the stack, these pointers
are changed to offsets before the reallocation and then changed back
to pointers after the reallocation.
'luaD_growstack' already checks that. This commit also fixes an
internal bug in 'luaD_growstack': a large 'n' could cause an arithmetic
overflow when computing 'needed'.
The pointer to the metamethod can be invalidated by a finalizer that
can run during a GC in 'checkstackGCp'. (This commit also fixes a
detail in the manual.) Bug introduced in commit 91673a8ec.
'luaD_pretailcall' mimics 'luaD_precall', handling call metamethods
and calling C functions directly. That makes the code in the
interpreter loop simpler.
This commit also goes back to emulating the tail call in 'luaD_precall'
with a goto, as C compilers may not do proper tail calls and the C
stack can overflow much sooner than the Lua stack (which grows as the
metamethod is added to it).
The parameters 'nresults' and 'delta1', in 'luaD_precall', were never
meaningful simultaneously. So, they were combined in a single parameter
'retdel'.
$he stack reallocation is done in two steps (allocation + free) because
the correction of the pointers pointing into the stack must be done
while both addresses (the old stack and the new one) are valid. In ISO
C, any pointer use after the pointer has been deallocated is undefined
behavior. The compiler option '-fsanitize=pointer-subtract' (plus what
it needs to work) complained about the old implementation.
More uses of macros 'likely'/'unlikely' (renamed to
'l_likely'/'l_unlikely'), both in range (extended to the
libraries) and in scope (extended to hooks, stack growth).
When, inside a coroutine, a C function with to-be-closed slots return,
the corresponding metamethods can yield. ('__close' metamethods called
through 'lua_closeslot' still cannot yield, as there is no continuation
to go when resuming.)
To-be-closed variables are linked in their own list, embedded into the
stack elements. (Due to alignment, this information does not change
the size of the stack elements in most architectures.) This new list
does not produce garbage and avoids memory errors when creating tbc
variables.
- 'L->top' is set once in 'luaD_hook', instead of being set in
'luaD_hookcall' and 'rethook';
- resume discard arguments when returning after an yield inside a hook
(arguments may interfere with the coroutine stack);
- yield inside a hook asserts it has no arguments.
The return hook should be called only after closing variables (which
are still part of the function). C functions were calling the hook
before the metamethods.
Completes commit b07fc10e91. '__close' metamethods can yield even
when they are being called due to an error. '__close' metamethods from
C functions are still not allowed to yield.
Initial implementation to allow yields inside '__close' metamethods.
This current version still does not allow a '__close' metamethod
to yield when called due to an error. '__close' metamethods from
C functions also are not allowed to yield.
When available, use the calling code to find a suitable name for what
was being called; this is particularly useful for errors of non-callable
metamethods. This commit also improved the debug information for
order metamethods.
