096e967aad
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.
133 lines
4.2 KiB
C
133 lines
4.2 KiB
C
/*
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* This file is part of the MicroPython project, http://micropython.org/
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*
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* The MIT License (MIT)
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*
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* Copyright (c) 2013, 2014 Damien P. George
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#ifndef MICROPY_INCLUDED_PY_NLR_H
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#define MICROPY_INCLUDED_PY_NLR_H
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// non-local return
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// exception handling, basically a stack of setjmp/longjmp buffers
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#include <limits.h>
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#include <setjmp.h>
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#include <assert.h>
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#include "py/mpconfig.h"
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typedef struct _nlr_buf_t nlr_buf_t;
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struct _nlr_buf_t {
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// the entries here must all be machine word size
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nlr_buf_t *prev;
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void *ret_val; // always a concrete object (an exception instance)
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#if !defined(MICROPY_NLR_SETJMP) || !MICROPY_NLR_SETJMP
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#if defined(__i386__)
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void *regs[6];
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#elif defined(__x86_64__)
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#if defined(__CYGWIN__)
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void *regs[12];
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#else
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void *regs[8];
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#endif
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#elif defined(__thumb2__) || defined(__thumb__) || defined(__arm__)
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void *regs[10];
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#elif defined(__xtensa__)
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void *regs[10];
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#else
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#define MICROPY_NLR_SETJMP (1)
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//#warning "No native NLR support for this arch, using setjmp implementation"
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#endif
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#endif
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#if MICROPY_NLR_SETJMP
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jmp_buf jmpbuf;
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#endif
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#if MICROPY_ENABLE_PYSTACK
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void *pystack;
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#endif
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};
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// Helper macros to save/restore the pystack state
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#if MICROPY_ENABLE_PYSTACK
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#define MP_NLR_SAVE_PYSTACK(nlr_buf) (nlr_buf)->pystack = MP_STATE_THREAD(pystack_cur)
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#define MP_NLR_RESTORE_PYSTACK(nlr_buf) MP_STATE_THREAD(pystack_cur) = (nlr_buf)->pystack
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#else
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#define MP_NLR_SAVE_PYSTACK(nlr_buf) (void)nlr_buf
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#define MP_NLR_RESTORE_PYSTACK(nlr_buf) (void)nlr_buf
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#endif
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#if MICROPY_NLR_SETJMP
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#include "py/mpstate.h"
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NORETURN void nlr_setjmp_jump(void *val);
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// nlr_push() must be defined as a macro, because "The stack context will be
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// invalidated if the function which called setjmp() returns."
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#define nlr_push(buf) ( \
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(buf)->prev = MP_STATE_THREAD(nlr_top), \
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MP_NLR_SAVE_PYSTACK(buf), \
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MP_STATE_THREAD(nlr_top) = (buf), \
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setjmp((buf)->jmpbuf))
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#define nlr_pop() { MP_STATE_THREAD(nlr_top) = MP_STATE_THREAD(nlr_top)->prev; }
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#define nlr_jump(val) nlr_setjmp_jump(val)
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#else
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unsigned int nlr_push(nlr_buf_t *);
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void nlr_pop(void);
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NORETURN void nlr_jump(void *val);
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#endif
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// This must be implemented by a port. It's called by nlr_jump
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// if no nlr buf has been pushed. It must not return, but rather
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// should bail out with a fatal error.
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NORETURN void nlr_jump_fail(void *val);
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// use nlr_raise instead of nlr_jump so that debugging is easier
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#ifndef MICROPY_DEBUG_NLR
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#define nlr_raise(val) nlr_jump(MP_OBJ_TO_PTR(val))
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#else
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#include "mpstate.h"
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#define nlr_raise(val) \
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do { \
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/*printf("nlr_raise: nlr_top=%p\n", MP_STATE_THREAD(nlr_top)); \
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fflush(stdout);*/ \
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void *_val = MP_OBJ_TO_PTR(val); \
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assert(_val != NULL); \
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assert(mp_obj_is_exception_instance(val)); \
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nlr_jump(_val); \
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} while (0)
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#if !MICROPY_NLR_SETJMP
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#define nlr_push(val) \
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assert(MP_STATE_THREAD(nlr_top) != val),nlr_push(val)
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/*
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#define nlr_push(val) \
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printf("nlr_push: before: nlr_top=%p, val=%p\n", MP_STATE_THREAD(nlr_top), val),assert(MP_STATE_THREAD(nlr_top) != val),nlr_push(val)
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#endif
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*/
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#endif
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#endif
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#endif // MICROPY_INCLUDED_PY_NLR_H
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