Commit Graph

14 Commits

Author SHA1 Message Date
Damien George 24aa81e1da py/nlrsetjmp: Use MP_NLR_JUMP_HEAD macro to simplify code.
Signed-off-by: Damien George <damien@micropython.org>
2023-06-02 21:47:34 +10:00
Damien George b25f92160b py/nlr: Factor out common NLR code to macro and generic funcs in nlr.c.
Each NLR implementation (Thumb, x86, x64, xtensa, setjmp) duplicates a lot
of the NLR code, specifically that dealing with pushing and popping the NLR
pointer to maintain the linked-list of NLR buffers.  This patch factors all
of that code out of the specific implementations into generic functions in
nlr.c, along with a helper macro in nlr.h.  This eliminates duplicated
code.
2017-12-28 16:46:30 +11:00
Paul Sokolovsky 096e967aad Revert "py/nlr: Factor out common NLR code to generic functions."
This reverts commit 6a3a742a6c.

The above commit has number of faults starting from the motivation down
to the actual implementation.

1. Faulty implementation.

The original code contained functions like:

NORETURN void nlr_jump(void *val) {
    nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
    nlr_buf_t *top = *top_ptr;
...
     __asm volatile (
    "mov    %0, %%edx           \n" // %edx points to nlr_buf
    "mov    28(%%edx), %%esi    \n" // load saved %esi
    "mov    24(%%edx), %%edi    \n" // load saved %edi
    "mov    20(%%edx), %%ebx    \n" // load saved %ebx
    "mov    16(%%edx), %%esp    \n" // load saved %esp
    "mov    12(%%edx), %%ebp    \n" // load saved %ebp
    "mov    8(%%edx), %%eax     \n" // load saved %eip
    "mov    %%eax, (%%esp)      \n" // store saved %eip to stack
    "xor    %%eax, %%eax        \n" // clear return register
    "inc    %%al                \n" // increase to make 1, non-local return
     "ret                        \n" // return
    :                               // output operands
    : "r"(top)                      // input operands
    :                               // clobbered registers
     );
}

Which clearly stated that C-level variable should be a parameter of the
assembly, whcih then moved it into correct register.

Whereas now it's:

NORETURN void nlr_jump_tail(nlr_buf_t *top) {
    (void)top;

    __asm volatile (
    "mov    28(%edx), %esi      \n" // load saved %esi
    "mov    24(%edx), %edi      \n" // load saved %edi
    "mov    20(%edx), %ebx      \n" // load saved %ebx
    "mov    16(%edx), %esp      \n" // load saved %esp
    "mov    12(%edx), %ebp      \n" // load saved %ebp
    "mov    8(%edx), %eax       \n" // load saved %eip
    "mov    %eax, (%esp)        \n" // store saved %eip to stack
    "xor    %eax, %eax          \n" // clear return register
    "inc    %al                 \n" // increase to make 1, non-local return
    "ret                        \n" // return
    );

    for (;;); // needed to silence compiler warning
}

Which just tries to perform operations on a completely random register (edx
in this case). The outcome is the expected: saving the pure random luck of
the compiler putting the right value in the random register above, there's
a crash.

2. Non-critical assessment.

The original commit message says "There is a small overhead introduced
(typically 1 machine instruction)". That machine instruction is a call
if a compiler doesn't perform tail optimization (happens regularly), and
it's 1 instruction only with the broken code shown above, fixing it
requires adding more. With inefficiencies already presented in the NLR
code, the overhead becomes "considerable" (several times more than 1%),
not "small".

The commit message also says "This eliminates duplicated code.". An
obvious way to eliminate duplication would be to factor out common code
to macros, not introduce overhead and breakage like above.

3. Faulty motivation.

All this started with a report of warnings/errors happening for a niche
compiler. It could have been solved in one the direct ways: a) fixing it
just for affected compiler(s); b) rewriting it in proper assembly (like
it was before BTW); c) by not doing anything at all, MICROPY_NLR_SETJMP
exists exactly to address minor-impact cases like thar (where a) or b) are
not applicable). Instead, a backwards "solution" was put forward, leading
to all the issues above.

The best action thus appears to be revert and rework, not trying to work
around what went haywire in the first place.
2017-12-26 19:27:58 +02:00
Damien George 6a3a742a6c py/nlr: Factor out common NLR code to generic functions.
Each NLR implementation (Thumb, x86, x64, xtensa, setjmp) duplicates a lot
of the NLR code, specifically that dealing with pushing and popping the NLR
pointer to maintain the linked-list of NLR buffers.  This patch factors all
of that code out of the specific implementations into generic functions in
nlr.c.  This eliminates duplicated code.

The factoring also allows to make the machine-specific NLR code pure
assembler code, thus allowing nlrthumb.c to use naked function attributes
in the correct way (naked functions can only have basic inline assembler
code in them).

There is a small overhead introduced (typically 1 machine instruction)
because now the generic nlr_jump() must call nlr_jump_tail() rather than
them being one combined function.
2017-12-20 15:42:06 +11:00
Damien George 02d830c035 py: Introduce a Python stack for scoped allocation.
This patch introduces the MICROPY_ENABLE_PYSTACK option (disabled by
default) which enables a "Python stack" that allows to allocate and free
memory in a scoped, or Last-In-First-Out (LIFO) way, similar to alloca().

A new memory allocation API is introduced along with this Py-stack.  It
includes both "local" and "nonlocal" LIFO allocation.  Local allocation is
intended to be equivalent to using alloca(), whereby the same function must
free the memory.  Nonlocal allocation is where another function may free
the memory, so long as it's still LIFO.

Follow-up patches will convert all uses of alloca() and VLA to the new
scoped allocation API.  The old behaviour (using alloca()) will still be
available, but when MICROPY_ENABLE_PYSTACK is enabled then alloca() is no
longer required or used.

The benefits of enabling this option are (or will be once subsequent
patches are made to convert alloca()/VLA):
- Toolchains without alloca() can use this feature to obtain correct and
  efficient scoped memory allocation (compared to using the heap instead
  of alloca(), which is slower).
- Even if alloca() is available, enabling the Py-stack gives slightly more
  efficient use of stack space when calling nested Python functions, due to
  the way that compilers implement alloca().
- Enabling the Py-stack with the stackless mode allows for even more
  efficient stack usage, as well as retaining high performance (because the
  heap is no longer used to build and destroy stackless code states).
- With Py-stack and stackless enabled, Python-calling-Python is no longer
  recursive in the C mp_execute_bytecode function.

The micropython.pystack_use() function is included to measure usage of the
Python stack.
2017-12-11 13:49:09 +11:00
Alexander Steffen 55f33240f3 all: Use the name MicroPython consistently in comments
There were several different spellings of MicroPython present in comments,
when there should be only one.
2017-07-31 18:35:40 +10:00
Damien George 08242eed26 py/nlrsetjmp: Add check for failed NLR jump.
Also optimise the function so it only needs to call the MP_STATE_THREAD
macro once (following how other nlr code is written).
2017-04-12 13:50:31 +10:00
Damien George 94238d4ae5 py/nlrsetjmp: Update to take into account new location of nlr_top.
It's now accessed via the MP_STATE_THREAD macro.
2016-06-28 11:28:52 +01:00
Damien George b4b10fd350 py: Put all global state together in state structures.
This patch consolidates all global variables in py/ core into one place,
in a global structure.  Root pointers are all located together to make
GC tracing easier and more efficient.
2015-01-07 20:33:00 +00:00
Damien George 8a2347723e py: Move global variable nlr_top to one place, in a .c file.
This reduces dependency on assembler, and allows to consolidate global
variables in the future.
2015-01-01 21:47:58 +00:00
Damien George 51dfcb4bb7 py: Move to guarded includes, everywhere in py/ core.
Addresses issue #1022.
2015-01-01 20:32:09 +00:00
Damien George 04b9147e15 Add license header to (almost) all files.
Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.
2014-05-03 23:27:38 +01:00
Paul Sokolovsky f54bcbf099 py, unix: Make "mpconfig.h" be first included, as other headers depend on it.
Specifically, nlr.h does.
2014-05-02 17:48:40 +03:00
Paul Sokolovsky 3a83b805fc nlr: Add implementation using setjmp/longjmp.
Having an optimized asm implementation is good, but if we want portability,
that's it.
2014-04-17 00:19:18 +03:00