From 63046d800d64081a4f7756476f5249179179ff5e Mon Sep 17 00:00:00 2001 From: Damien George Date: Mon, 19 Aug 2019 15:50:02 +1000 Subject: [PATCH 1/3] py: Introduce MP_UNREACHABLE macro to annotate unreachable code. And use it to replace the same pattern at the end of nlrthumb.c:nlr_jump. --- py/mpconfig.h | 9 +++++++++ py/nlrthumb.c | 6 +----- 2 files changed, 10 insertions(+), 5 deletions(-) diff --git a/py/mpconfig.h b/py/mpconfig.h index 3ec383817e..a0d211bfaa 100755 --- a/py/mpconfig.h +++ b/py/mpconfig.h @@ -1440,6 +1440,15 @@ typedef double mp_float_t; #define MP_UNLIKELY(x) __builtin_expect((x), 0) #endif +// To annotate that code is unreachable +#ifndef MP_UNREACHABLE +#if defined(__GNUC__) +#define MP_UNREACHABLE __builtin_unreachable(); +#else +#define MP_UNREACHABLE for (;;); +#endif +#endif + #ifndef MP_HTOBE16 #if MP_ENDIANNESS_LITTLE # define MP_HTOBE16(x) ((uint16_t)( (((x) & 0xff) << 8) | (((x) >> 8) & 0xff) )) diff --git a/py/nlrthumb.c b/py/nlrthumb.c index 69d3f868af..eb32e2ce5b 100644 --- a/py/nlrthumb.c +++ b/py/nlrthumb.c @@ -127,11 +127,7 @@ NORETURN void nlr_jump(void *val) { : // clobbered registers ); - #if defined(__GNUC__) - __builtin_unreachable(); - #else - for (;;); // needed to silence compiler warning - #endif + MP_UNREACHABLE } #endif // MICROPY_NLR_THUMB From 1cf0ce094a4a1571b7404643e7a3b992592317a5 Mon Sep 17 00:00:00 2001 From: Damien George Date: Mon, 19 Aug 2019 15:51:40 +1000 Subject: [PATCH 2/3] 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. --- py/nlrx64.c | 2 +- py/nlrx86.c | 2 +- py/nlrxtensa.c | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/py/nlrx64.c b/py/nlrx64.c index 9b2b22c225..569ad84fb0 100644 --- a/py/nlrx64.c +++ b/py/nlrx64.c @@ -108,7 +108,7 @@ NORETURN void nlr_jump(void *val) { : // clobbered registers ); - for (;;); // needed to silence compiler warning + MP_UNREACHABLE } #endif // MICROPY_NLR_X64 diff --git a/py/nlrx86.c b/py/nlrx86.c index 4900a4c0d2..6fbbe44327 100644 --- a/py/nlrx86.c +++ b/py/nlrx86.c @@ -100,7 +100,7 @@ NORETURN void nlr_jump(void *val) { : // clobbered registers ); - for (;;); // needed to silence compiler warning + MP_UNREACHABLE } #endif // MICROPY_NLR_X86 diff --git a/py/nlrxtensa.c b/py/nlrxtensa.c index d66c7a9a7f..5640350043 100644 --- a/py/nlrxtensa.c +++ b/py/nlrxtensa.c @@ -77,7 +77,7 @@ NORETURN void nlr_jump(void *val) { : // clobbered registers ); - for (;;); // needed to silence compiler warning + MP_UNREACHABLE } #endif // MICROPY_NLR_XTENSA From 767d47dd6025e8046b03e6b307fd0ba6a81cf504 Mon Sep 17 00:00:00 2001 From: Damien George Date: Mon, 17 Jun 2019 23:19:34 +1000 Subject: [PATCH 3/3] py/nlrthumb: Save and restore VFP registers s16-s21 when CPU has them. These s16-s21 registers are used by gcc so need to be saved. Future versions of gcc (beyond v9.1.0), or other compilers, may eventually need additional registers saved/restored. See issue #4844. --- py/nlr.h | 9 ++++++++- py/nlrthumb.c | 10 ++++++++++ 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/py/nlr.h b/py/nlr.h index b442aaf8a0..1b95002d3b 100644 --- a/py/nlr.h +++ b/py/nlr.h @@ -54,7 +54,14 @@ #endif #elif defined(__thumb2__) || defined(__thumb__) || defined(__arm__) #define MICROPY_NLR_THUMB (1) - #define MICROPY_NLR_NUM_REGS (10) + #if defined(__SOFTFP__) + #define MICROPY_NLR_NUM_REGS (10) + #else + // With hardware FP registers s16-s31 are callee save so in principle + // should be saved and restored by the NLR code. gcc only uses s16-s21 + // so only save/restore those as an optimisation. + #define MICROPY_NLR_NUM_REGS (10 + 6) + #endif #elif defined(__xtensa__) #define MICROPY_NLR_XTENSA (1) #define MICROPY_NLR_NUM_REGS (10) diff --git a/py/nlrthumb.c b/py/nlrthumb.c index eb32e2ce5b..056aa358e7 100644 --- a/py/nlrthumb.c +++ b/py/nlrthumb.c @@ -63,6 +63,11 @@ __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) { "str r10, [r0, #36] \n" // store r10 into nlr_buf "str r11, [r0, #40] \n" // store r11 into nlr_buf "str r13, [r0, #44] \n" // store r13=sp into nlr_buf + #if MICROPY_NLR_NUM_REGS == 16 + "vstr d8, [r0, #48] \n" // store s16-s17 into nlr_buf + "vstr d9, [r0, #56] \n" // store s18-s19 into nlr_buf + "vstr d10, [r0, #64] \n" // store s20-s21 into nlr_buf + #endif "str lr, [r0, #8] \n" // store lr into nlr_buf #endif @@ -118,6 +123,11 @@ NORETURN void nlr_jump(void *val) { "ldr r10, [r0, #36] \n" // load r10 from nlr_buf "ldr r11, [r0, #40] \n" // load r11 from nlr_buf "ldr r13, [r0, #44] \n" // load r13=sp from nlr_buf + #if MICROPY_NLR_NUM_REGS == 16 + "vldr d8, [r0, #48] \n" // load s16-s17 from nlr_buf + "vldr d9, [r0, #56] \n" // load s18-s19 from nlr_buf + "vldr d10, [r0, #64] \n" // load s20-s21 from nlr_buf + #endif "ldr lr, [r0, #8] \n" // load lr from nlr_buf #endif "movs r0, #1 \n" // return 1, non-local return