micropython: Add patch to avoid textrel on arm/thumb
Signed-off-by: J. Neuschäfer <j.neuschaefer@gmx.net> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
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J. Neuschäfer
Yann E. MORIN
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From 7b050b366b7dacfb43779c51702a892d8f1873d0 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?J=2E=20Neusch=C3=A4fer?= <j.ne@posteo.net>
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Date: Sun, 2 Apr 2023 19:58:42 +0200
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Subject: [PATCH] py/nlrthumb: Make non-Thumb2 long-jump workaround opt-in.
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Although the original motivation given for the workaround[1] is correct,
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nlr.o and nlrthumb.o are linked with a small enough distance that the
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problem does not occur, and the workaround isn't necessary. The distance
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between the b instruction and its target (nlr_push_tail) is just 64
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bytes[2], well within the ±2046 byte range addressable by an
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unconditional branch instruction in Thumb mode.
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The workaround induces a relocation in the text section (textrel), which
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isn't supported everywhere, notably not on musl-libc[3], where it causes
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a crash on start-up. With the workaround removed, micropython works on an
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ARMv5T Linux system built with musl-libc.
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This commit changes nlrthumb.c to use a direct jump by default, but
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leaves the long jump workaround as an option for those cases where it's
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actually needed.
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[1]: commit dd376a239dc4f47b0ee7866810fcda151f3cf6dd
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Author: Damien George <damien.p.george@gmail.com>
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Date: Fri Sep 1 15:25:29 2017 +1000
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py/nlrthumb: Get working again on standard Thumb arch (ie not Thumb2).
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"b" on Thumb might not be long enough for the jump to nlr_push_tail so
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it must be done indirectly.
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[2]: Excerpt from objdump -d micropython:
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000095c4 <nlr_push_tail>:
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95c4: b510 push {r4, lr}
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95c6: 0004 movs r4, r0
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95c8: f02d fd42 bl 37050 <mp_thread_get_state>
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95cc: 6943 ldr r3, [r0, #20]
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95ce: 6023 str r3, [r4, #0]
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95d0: 6144 str r4, [r0, #20]
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95d2: 2000 movs r0, #0
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95d4: bd10 pop {r4, pc}
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000095d6 <nlr_pop>:
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95d6: b510 push {r4, lr}
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95d8: f02d fd3a bl 37050 <mp_thread_get_state>
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95dc: 6943 ldr r3, [r0, #20]
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95de: 681b ldr r3, [r3, #0]
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95e0: 6143 str r3, [r0, #20]
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95e2: bd10 pop {r4, pc}
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000095e4 <nlr_push>:
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95e4: 60c4 str r4, [r0, #12]
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95e6: 6105 str r5, [r0, #16]
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95e8: 6146 str r6, [r0, #20]
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95ea: 6187 str r7, [r0, #24]
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95ec: 4641 mov r1, r8
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95ee: 61c1 str r1, [r0, #28]
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95f0: 4649 mov r1, r9
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95f2: 6201 str r1, [r0, #32]
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95f4: 4651 mov r1, sl
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95f6: 6241 str r1, [r0, #36] @ 0x24
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95f8: 4659 mov r1, fp
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95fa: 6281 str r1, [r0, #40] @ 0x28
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95fc: 4669 mov r1, sp
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95fe: 62c1 str r1, [r0, #44] @ 0x2c
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9600: 4671 mov r1, lr
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9602: 6081 str r1, [r0, #8]
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9604: e7de b.n 95c4 <nlr_push_tail>
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[3]: https://www.openwall.com/lists/musl/2020/09/25/4
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Signed-off-by: J. Neuschäfer <j.ne@posteo.net>
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Upstream: https://github.com/micropython/micropython/commit/7b050b366b7dacfb43779c51702a892d8f1873d0
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---
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py/mpconfig.h | 6 ++++++
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py/nlrthumb.c | 10 +++++++++-
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2 files changed, 15 insertions(+), 1 deletion(-)
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diff --git a/py/mpconfig.h b/py/mpconfig.h
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index af2480266..1aa3e0699 100644
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--- a/py/mpconfig.h
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+++ b/py/mpconfig.h
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@@ -587,6 +587,12 @@
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/*****************************************************************************/
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/* Python internal features */
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+// Use a special long jump in nlrthumb.c, which may be necessary if nlr.o and
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+// nlrthumb.o are linked far apart from each other.
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+#ifndef MICROPY_NLR_THUMB_USE_LONG_JUMP
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+#define MICROPY_NLR_THUMB_USE_LONG_JUMP (0)
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+#endif
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+
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// Whether to enable import of external modules
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// When disabled, only importing of built-in modules is supported
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// When enabled, a port must implement mp_import_stat (among other things)
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diff --git a/py/nlrthumb.c b/py/nlrthumb.c
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index a22c5df5b..e7b24f242 100644
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--- a/py/nlrthumb.c
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+++ b/py/nlrthumb.c
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@@ -38,6 +38,14 @@
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__attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
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+ // If you get a linker error here, indicating that a relocation doesn't
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+ // fit, try the following (in that order):
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+ //
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+ // 1. Ensure that nlr.o nlrthumb.o are linked closely together, i.e.
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+ // there aren't too many other files between them in the linker list
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+ // (PY_CORE_O_BASENAME in py/py.mk)
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+ // 2. Set -DMICROPY_NLR_THUMB_USE_LONG_JUMP=1 during the build
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+ //
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__asm volatile (
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"str r4, [r0, #12] \n" // store r4 into nlr_buf
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"str r5, [r0, #16] \n" // store r5 into nlr_buf
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@@ -71,7 +79,7 @@ __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
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"str lr, [r0, #8] \n" // store lr into nlr_buf
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#endif
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- #if !defined(__thumb2__)
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+ #if MICROPY_NLR_THUMB_USE_LONG_JUMP
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"ldr r1, nlr_push_tail_var \n"
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"bx r1 \n" // do the rest in C
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".align 2 \n"
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--
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2.43.0
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