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Revert "py/nlr: Factor out common NLR code to generic functions."

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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.
This commit is contained in:
Paul Sokolovsky 2017-12-26 18:39:51 +02:00
parent d9977a8ad9
commit 096e967aad
8 changed files with 206 additions and 159 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

74
py/nlr.c
View File

@ -1,74 +0,0 @@
/*
* This file is part of the MicroPython project, http://micropython.org/
*
* The MIT License (MIT)
*
* Copyright (c) 2013-2017 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"
// Helper macros to save/restore the pystack state
#if MICROPY_ENABLE_PYSTACK
#define MP_NLR_SAVE_PYSTACK(nlr_buf) (nlr_buf)->pystack = MP_STATE_THREAD(pystack_cur)
#define MP_NLR_RESTORE_PYSTACK(nlr_buf) MP_STATE_THREAD(pystack_cur) = (nlr_buf)->pystack
#else
#define MP_NLR_SAVE_PYSTACK(nlr_buf) (void)nlr_buf
#define MP_NLR_RESTORE_PYSTACK(nlr_buf) (void)nlr_buf
#endif
#if !MICROPY_NLR_SETJMP
// When not using setjmp, nlr_push_tail is called from inline asm so needs special care
#if MICROPY_NLR_X86 && (defined(_WIN32) || defined(__CYGWIN__))
// On these 32-bit platforms make sure nlr_push_tail doesn't have a leading underscore
unsigned int nlr_push_tail(nlr_buf_t *nlr) asm("nlr_push_tail");
#else
// LTO can't see inside inline asm functions so explicitly mark nlr_push_tail as used
__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr);
#endif
#endif
unsigned int nlr_push_tail(nlr_buf_t *nlr) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
nlr->prev = *top;
MP_NLR_SAVE_PYSTACK(nlr);
*top = nlr;
return 0; // normal return
}
void nlr_pop(void) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
*top = (*top)->prev;
}
NORETURN void nlr_jump(void *val) {
nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
nlr_buf_t *top = *top_ptr;
if (top == NULL) {
nlr_jump_fail(val);
}
top->ret_val = val;
MP_NLR_RESTORE_PYSTACK(top);
*top_ptr = top->prev;
nlr_jump_tail(top);
}

67
py/nlr.h
View File

@ -30,49 +30,37 @@
// exception handling, basically a stack of setjmp/longjmp buffers
#include <limits.h>
#include <setjmp.h>
#include <assert.h>
#include "py/mpconfig.h"
// If MICROPY_NLR_SETJMP is not enabled then auto-detect the machine arch
// Allow a port to set MICROPY_NLR_NUM_REGS to define their own implementation
#if !MICROPY_NLR_SETJMP && !defined(MICROPY_NLR_NUM_REGS)
typedef struct _nlr_buf_t nlr_buf_t;
struct _nlr_buf_t {
// the entries here must all be machine word size
nlr_buf_t *prev;
void *ret_val; // always a concrete object (an exception instance)
#if !defined(MICROPY_NLR_SETJMP) || !MICROPY_NLR_SETJMP
#if defined(__i386__)
#define MICROPY_NLR_X86 (1)
#define MICROPY_NLR_NUM_REGS (6)
void *regs[6];
#elif defined(__x86_64__)
#define MICROPY_NLR_X64 (1)
#if defined(__CYGWIN__)
#define MICROPY_NLR_NUM_REGS (12)
void *regs[12];
#else
#define MICROPY_NLR_NUM_REGS (8)
void *regs[8];
#endif
#elif defined(__thumb2__) || defined(__thumb__) || defined(__arm__)
#define MICROPY_NLR_THUMB (1)
#define MICROPY_NLR_NUM_REGS (10)
void *regs[10];
#elif defined(__xtensa__)
#define MICROPY_NLR_XTENSA (1)
#define MICROPY_NLR_NUM_REGS (10)
void *regs[10];
#else
#define MICROPY_NLR_SETJMP (1)
//#warning "No native NLR support for this arch, using setjmp implementation"
#endif
#endif
#if MICROPY_NLR_SETJMP
#include <setjmp.h>
#endif
typedef struct _nlr_buf_t nlr_buf_t;
struct _nlr_buf_t {
// the entries here must all be machine word size
nlr_buf_t *prev;
void *ret_val; // always a concrete object (an exception instance)
#if MICROPY_NLR_SETJMP
jmp_buf jmpbuf;
#else
void *regs[MICROPY_NLR_NUM_REGS];
#endif
#if MICROPY_ENABLE_PYSTACK
@ -80,19 +68,33 @@ struct _nlr_buf_t {
#endif
};
#if MICROPY_NLR_SETJMP
// nlr_push() must be defined as a macro, because "The stack context will be
// invalidated if the function which called setjmp() returns."
// For this case it is safe to call nlr_push_tail() first.
#define nlr_push(buf) (nlr_push_tail(buf), setjmp((buf)->jmpbuf))
// Helper macros to save/restore the pystack state
#if MICROPY_ENABLE_PYSTACK
#define MP_NLR_SAVE_PYSTACK(nlr_buf) (nlr_buf)->pystack = MP_STATE_THREAD(pystack_cur)
#define MP_NLR_RESTORE_PYSTACK(nlr_buf) MP_STATE_THREAD(pystack_cur) = (nlr_buf)->pystack
#else
unsigned int nlr_push(nlr_buf_t *);
#define MP_NLR_SAVE_PYSTACK(nlr_buf) (void)nlr_buf
#define MP_NLR_RESTORE_PYSTACK(nlr_buf) (void)nlr_buf
#endif
unsigned int nlr_push_tail(nlr_buf_t *top);
#if MICROPY_NLR_SETJMP
#include "py/mpstate.h"
NORETURN void nlr_setjmp_jump(void *val);
// nlr_push() must be defined as a macro, because "The stack context will be
// invalidated if the function which called setjmp() returns."
#define nlr_push(buf) ( \
(buf)->prev = MP_STATE_THREAD(nlr_top), \
MP_NLR_SAVE_PYSTACK(buf), \
MP_STATE_THREAD(nlr_top) = (buf), \
setjmp((buf)->jmpbuf))
#define nlr_pop() { MP_STATE_THREAD(nlr_top) = MP_STATE_THREAD(nlr_top)->prev; }
#define nlr_jump(val) nlr_setjmp_jump(val)
#else
unsigned int nlr_push(nlr_buf_t *);
void nlr_pop(void);
NORETURN void nlr_jump(void *val);
NORETURN void nlr_jump_tail(nlr_buf_t *top);
#endif
// This must be implemented by a port. It's called by nlr_jump
// if no nlr buf has been pushed. It must not return, but rather
@ -121,6 +123,7 @@ NORETURN void nlr_jump_fail(void *val);
/*
#define nlr_push(val) \
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)
#endif
*/
#endif

10
py/nlrsetjmp.c
View File

@ -28,7 +28,15 @@
#if MICROPY_NLR_SETJMP
NORETURN void nlr_jump_tail(nlr_buf_t *top) {
void nlr_setjmp_jump(void *val) {
nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
nlr_buf_t *top = *top_ptr;
if (top == NULL) {
nlr_jump_fail(val);
}
top->ret_val = val;
MP_NLR_RESTORE_PYSTACK(top);
*top_ptr = top->prev;
longjmp(top->jmpbuf, 1);
}

38
py/nlrthumb.c
View File

@ -26,7 +26,7 @@
#include "py/mpstate.h"
#if MICROPY_NLR_THUMB
#if (!defined(MICROPY_NLR_SETJMP) || !MICROPY_NLR_SETJMP) && (defined(__thumb2__) || defined(__thumb__) || defined(__arm__))
#undef nlr_push
@ -37,6 +37,7 @@
// r4-r11, r13=sp
__attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
__asm volatile (
"str r4, [r0, #12] \n" // store r4 into nlr_buf
"str r5, [r0, #16] \n" // store r5 into nlr_buf
@ -74,10 +75,36 @@ __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
"b nlr_push_tail \n" // do the rest in C
#endif
);
return 0; // needed to silence compiler warning
}
NORETURN __attribute__((naked)) void nlr_jump_tail(nlr_buf_t *top) {
__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
nlr->prev = *top;
MP_NLR_SAVE_PYSTACK(nlr);
*top = nlr;
return 0; // normal return
}
void nlr_pop(void) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
*top = (*top)->prev;
}
NORETURN __attribute__((naked)) void nlr_jump(void *val) {
nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
nlr_buf_t *top = *top_ptr;
if (top == NULL) {
nlr_jump_fail(val);
}
top->ret_val = val;
MP_NLR_RESTORE_PYSTACK(top);
*top_ptr = top->prev;
__asm volatile (
"mov r0, %0 \n" // r0 points to nlr_buf
"ldr r4, [r0, #12] \n" // load r4 from nlr_buf
"ldr r5, [r0, #16] \n" // load r5 from nlr_buf
"ldr r6, [r0, #20] \n" // load r6 from nlr_buf
@ -106,7 +133,12 @@ NORETURN __attribute__((naked)) void nlr_jump_tail(nlr_buf_t *top) {
#endif
"movs r0, #1 \n" // return 1, non-local return
"bx lr \n" // return
: // output operands
: "r"(top) // input operands
: // clobbered registers
);
for (;;); // needed to silence compiler warning
}
#endif // MICROPY_NLR_THUMB
#endif // (!defined(MICROPY_NLR_SETJMP) || !MICROPY_NLR_SETJMP) && (defined(__thumb2__) || defined(__thumb__) || defined(__arm__))

70
py/nlrx64.c
View File

@ -26,7 +26,7 @@
#include "py/mpstate.h"
#if MICROPY_NLR_X64
#if !MICROPY_NLR_SETJMP && defined(__x86_64__)
#undef nlr_push
@ -39,6 +39,8 @@
#define NLR_OS_WINDOWS 0
#endif
__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr);
unsigned int nlr_push(nlr_buf_t *nlr) {
(void)nlr;
@ -86,38 +88,54 @@ unsigned int nlr_push(nlr_buf_t *nlr) {
return 0; // needed to silence compiler warning
}
NORETURN void nlr_jump_tail(nlr_buf_t *top) {
(void)top;
__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
nlr->prev = *top;
MP_NLR_SAVE_PYSTACK(nlr);
*top = nlr;
return 0; // normal return
}
void nlr_pop(void) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
*top = (*top)->prev;
}
NORETURN void nlr_jump(void *val) {
nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
nlr_buf_t *top = *top_ptr;
if (top == NULL) {
nlr_jump_fail(val);
}
top->ret_val = val;
MP_NLR_RESTORE_PYSTACK(top);
*top_ptr = top->prev;
__asm volatile (
"movq %0, %%rcx \n" // %rcx points to nlr_buf
#if NLR_OS_WINDOWS
"movq 88(%rcx), %rsi \n" // load saved %rsi
"movq 80(%rcx), %rdi \n" // load saved %rdr
"movq 72(%rcx), %r15 \n" // load saved %r15
"movq 64(%rcx), %r14 \n" // load saved %r14
"movq 56(%rcx), %r13 \n" // load saved %r13
"movq 48(%rcx), %r12 \n" // load saved %r12
"movq 40(%rcx), %rbx \n" // load saved %rbx
"movq 32(%rcx), %rsp \n" // load saved %rsp
"movq 24(%rcx), %rbp \n" // load saved %rbp
"movq 16(%rcx), %rax \n" // load saved %rip
#else
"movq 72(%rdi), %r15 \n" // load saved %r15
"movq 64(%rdi), %r14 \n" // load saved %r14
"movq 56(%rdi), %r13 \n" // load saved %r13
"movq 48(%rdi), %r12 \n" // load saved %r12
"movq 40(%rdi), %rbx \n" // load saved %rbx
"movq 32(%rdi), %rsp \n" // load saved %rsp
"movq 24(%rdi), %rbp \n" // load saved %rbp
"movq 16(%rdi), %rax \n" // load saved %rip
"movq 88(%%rcx), %%rsi \n" // load saved %rsi
"movq 80(%%rcx), %%rdi \n" // load saved %rdr
#endif
"movq %rax, (%rsp) \n" // store saved %rip to stack
"xorq %rax, %rax \n" // clear return register
"inc %al \n" // increase to make 1, non-local return
"movq 72(%%rcx), %%r15 \n" // load saved %r15
"movq 64(%%rcx), %%r14 \n" // load saved %r14
"movq 56(%%rcx), %%r13 \n" // load saved %r13
"movq 48(%%rcx), %%r12 \n" // load saved %r12
"movq 40(%%rcx), %%rbx \n" // load saved %rbx
"movq 32(%%rcx), %%rsp \n" // load saved %rsp
"movq 24(%%rcx), %%rbp \n" // load saved %rbp
"movq 16(%%rcx), %%rax \n" // load saved %rip
"movq %%rax, (%%rsp) \n" // store saved %rip to stack
"xorq %%rax, %%rax \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
);
for (;;); // needed to silence compiler warning
}
#endif // MICROPY_NLR_X64
#endif // !MICROPY_NLR_SETJMP && defined(__x86_64__)

63
py/nlrx86.c
View File

@ -26,13 +26,25 @@
#include "py/mpstate.h"
#if MICROPY_NLR_X86
#if !MICROPY_NLR_SETJMP && defined(__i386__)
#undef nlr_push
// For reference, x86 callee save regs are:
// ebx, esi, edi, ebp, esp, eip
#if defined(_WIN32) || defined(__CYGWIN__)
#define NLR_OS_WINDOWS 1
#else
#define NLR_OS_WINDOWS 0
#endif
#if NLR_OS_WINDOWS
unsigned int nlr_push_tail(nlr_buf_t *nlr) asm("nlr_push_tail");
#else
__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr);
#endif
unsigned int nlr_push(nlr_buf_t *nlr) {
(void)nlr;
@ -58,23 +70,48 @@ unsigned int nlr_push(nlr_buf_t *nlr) {
return 0; // needed to silence compiler warning
}
NORETURN void nlr_jump_tail(nlr_buf_t *top) {
(void)top;
__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
nlr->prev = *top;
MP_NLR_SAVE_PYSTACK(nlr);
*top = nlr;
return 0; // normal return
}
void nlr_pop(void) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
*top = (*top)->prev;
}
NORETURN void nlr_jump(void *val) {
nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
nlr_buf_t *top = *top_ptr;
if (top == NULL) {
nlr_jump_fail(val);
}
top->ret_val = val;
MP_NLR_RESTORE_PYSTACK(top);
*top_ptr = top->prev;
__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
"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
);
for (;;); // needed to silence compiler warning
}
#endif // MICROPY_NLR_X86
#endif // !MICROPY_NLR_SETJMP && defined(__i386__)

34
py/nlrxtensa.c
View File

@ -26,7 +26,7 @@
#include "py/mpstate.h"
#if MICROPY_NLR_XTENSA
#if !MICROPY_NLR_SETJMP && defined(__xtensa__)
#undef nlr_push
@ -37,7 +37,6 @@
// a3-a7 = rest of args
unsigned int nlr_push(nlr_buf_t *nlr) {
(void)nlr;
__asm volatile (
"s32i.n a0, a2, 8 \n" // save regs...
@ -56,10 +55,32 @@ unsigned int nlr_push(nlr_buf_t *nlr) {
return 0; // needed to silence compiler warning
}
NORETURN void nlr_jump_tail(nlr_buf_t *top) {
(void)top;
__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
nlr->prev = *top;
MP_NLR_SAVE_PYSTACK(nlr);
*top = nlr;
return 0; // normal return
}
void nlr_pop(void) {
nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
*top = (*top)->prev;
}
NORETURN void nlr_jump(void *val) {
nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
nlr_buf_t *top = *top_ptr;
if (top == NULL) {
nlr_jump_fail(val);
}
top->ret_val = val;
MP_NLR_RESTORE_PYSTACK(top);
*top_ptr = top->prev;
__asm volatile (
"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"
@ -72,9 +93,12 @@ NORETURN void nlr_jump_tail(nlr_buf_t *top) {
"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
);
for (;;); // needed to silence compiler warning
}
#endif // MICROPY_NLR_XTENSA
#endif // !MICROPY_NLR_SETJMP && defined(__xtensa__)

1
py/py.mk
View File

@ -103,7 +103,6 @@ endif
# py object files
PY_O_BASENAME = \
mpstate.o \
nlr.o \
nlrx86.o \
nlrx64.o \
nlrthumb.o \