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micropython/py/nlrxtensa.c

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py/nlrxtensa: Convert from assembler to C file with inline asm. nlr_jump is a little bit inefficient because it now saves a register to the stack.
2017-02-16 06:23:29 +00:00
/*
* This file is part of the MicroPython project, http://micropython.org/
*
* The MIT License (MIT)
*
* Copyright (c) 2014-2017 Damien P. George
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "py/mpstate.h"
py/nlr: Clean up selection and config of NLR implementation. If MICROPY_NLR_SETJMP is not enabled and the machine is auto-detected then nlr.h now defines some convenience macros for the individual NLR implementations to use (eg MICROPY_NLR_THUMB). This keeps nlr.h and the implementation in sync, and also makes the nlr_buf_t struct easier to read.
2017-12-28 05:18:39 +00:00
#if MICROPY_NLR_XTENSA
py/nlrxtensa: Convert from assembler to C file with inline asm. nlr_jump is a little bit inefficient because it now saves a register to the stack.
2017-02-16 06:23:29 +00:00
#undef nlr_push
// Xtensa calling conventions:
// a0 = return address
// a1 = stack pointer
// a2 = first arg, return value
// a3-a7 = rest of args
unsigned int nlr_push(nlr_buf_t *nlr) {
__asm volatile (
all: Reformat C and Python source code with tools/codeformat.py. This is run with uncrustify 0.70.1, and black 19.10b0.
2020-02-27 04:36:53 +00:00
"s32i.n a0, a2, 8 \n" // save regs...
"s32i.n a1, a2, 12 \n"
"s32i.n a8, a2, 16 \n"
"s32i.n a9, a2, 20 \n"
"s32i.n a10, a2, 24 \n"
"s32i.n a11, a2, 28 \n"
"s32i.n a12, a2, 32 \n"
"s32i.n a13, a2, 36 \n"
"s32i.n a14, a2, 40 \n"
"s32i.n a15, a2, 44 \n"
"j nlr_push_tail \n" // do the rest in C
);
py/nlrxtensa: Convert from assembler to C file with inline asm. nlr_jump is a little bit inefficient because it now saves a register to the stack.
2017-02-16 06:23:29 +00:00
return 0; // needed to silence compiler warning
}
Revert "py/nlr: Factor out common NLR code to generic functions." This reverts commit 6a3a742a6c9caaa2be0fd0aac7a5df4ac816081c. 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 16:39:51 +00:00
NORETURN void nlr_jump(void *val) {
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 05:46:30 +00:00
MP_NLR_JUMP_HEAD(val, top)
py/nlrxtensa: Convert from assembler to C file with inline asm. nlr_jump is a little bit inefficient because it now saves a register to the stack.
2017-02-16 06:23:29 +00:00
__asm volatile (
all: Reformat C and Python source code with tools/codeformat.py. This is run with uncrustify 0.70.1, and black 19.10b0.
2020-02-27 04:36:53 +00:00
"mov.n a2, %0 \n" // a2 points to nlr_buf
"l32i.n a0, a2, 8 \n" // restore regs...
"l32i.n a1, a2, 12 \n"
"l32i.n a8, a2, 16 \n"
"l32i.n a9, a2, 20 \n"
"l32i.n a10, a2, 24 \n"
"l32i.n a11, a2, 28 \n"
"l32i.n a12, a2, 32 \n"
"l32i.n a13, a2, 36 \n"
"l32i.n a14, a2, 40 \n"
"l32i.n a15, a2, 44 \n"
"movi.n a2, 1 \n" // return 1, non-local return
"ret.n \n" // return
: // output operands
: "r" (top) // input operands
: // clobbered registers
);
py/nlrxtensa: Convert from assembler to C file with inline asm. nlr_jump is a little bit inefficient because it now saves a register to the stack.
2017-02-16 06:23:29 +00:00
py/nlr: Use MP_UNREACHABLE at the end of arch-specific nlr_jump funcs. Recent versions of gcc perform optimisations which can lead to the following code from the MP_NLR_JUMP_HEAD macro being omitted: top->ret_val = val; \ MP_NLR_RESTORE_PYSTACK(top); \ *_top_ptr = top->prev; \ This is noticeable (at least) in the unix coverage on x86-64 built with gcc 9.1.0. This is because the nlr_jump function is marked as no-return, so gcc deduces that the above code has no effect. Adding MP_UNREACHABLE tells the compiler that the asm code may branch elsewhere, and so it cannot optimise away the code.
2019-08-19 05:51:40 +00:00
MP_UNREACHABLE
py/nlrxtensa: Convert from assembler to C file with inline asm. nlr_jump is a little bit inefficient because it now saves a register to the stack.
2017-02-16 06:23:29 +00:00
}
py/nlr: Clean up selection and config of NLR implementation. If MICROPY_NLR_SETJMP is not enabled and the machine is auto-detected then nlr.h now defines some convenience macros for the individual NLR implementations to use (eg MICROPY_NLR_THUMB). This keeps nlr.h and the implementation in sync, and also makes the nlr_buf_t struct easier to read.
2017-12-28 05:18:39 +00:00
#endif // MICROPY_NLR_XTENSA