MicroPython doesn't work on recent Android SDKs
Building MicroPython for armeabi-v7a will result in code having some relocation. This is not accepted on recent Android API levels.
The problem comes from the non-local return routine. On ARM64 it works well because we essentially use setjmp. It seems to be working fine on x86 and x86_64 as well, probably because the code in nlrx86.c and nlrx64.c is kosher in that regard. But the code in nrlthumb.c seems to be generating code with relocation, which Android will outright refuse to load.
There are two options to fix this:
- Always define
MICROPY_NLR_SETJMPwhen building for Android - Fix
nrlthumb.cto not generate text relocations, or to have an option not to
py/nlrthumb: Make non-Thumb2 workaround opt-in.
py/nlrthumb: Make non-Thumb2 workaround opt-in.
Although the original motivation given for the workaround[1] is correct,
nlr.o and nlrthumb.o are linked with a small enough distance that the
problem does not occur, and the workaround isn't necessary. The distance
between the b instruction and its target (nlr_push_tail) is just 64
bytes[2], well within the ±2046 byte range addressable by an
unconditional branch instruction in Thumb mode.
The workaround induces a relocation in the text section (textrel), which
isn't supported everywhere, notably not on musl-libc3, where it causes
a crash on start-up. With the workaround removed, micropython works on an
ARMv5T Linux system built with musl-libc.
This commit changes nlrthumb.c to use a direct jump by default, but
leaves the long jump workaround as an option for those cases where it's
actually needed.
[1]: commit dd376a239dc4f47b0ee7866810fcda151f3cf6dd
Author: Damien George damien.p.george@gmail.com
Date: Fri Sep 1 15:25:29 2017 +1000
py/nlrthumb: Get working again on standard Thumb arch (ie not Thumb2).
"b" on Thumb might not be long enough for the jump to nlr_push_tail so
it must be done indirectly.
[2]: Excerpt from objdump -d micropython:
000095c4 <nlr_push_tail>:
95c4: b510 push {r4, lr}
95c6: 0004 movs r4, r0
95c8: f02d fd42 bl 37050 <mp_thread_get_state>
95cc: 6943 ldr r3, [r0, #20]
95ce: 6023 str r3, [r4, #0]
95d0: 6144 str r4, [r0, #20]
95d2: 2000 movs r0, #0
95d4: bd10 pop {r4, pc}
000095d6 <nlr_pop>:
95d6: b510 push {r4, lr}
95d8: f02d fd3a bl 37050 <mp_thread_get_state>
95dc: 6943 ldr r3, [r0, #20]
95de: 681b ldr r3, [r3, #0]
95e0: 6143 str r3, [r0, #20]
95e2: bd10 pop {r4, pc}
000095e4 <nlr_push>:
95e4: 60c4 str r4, [r0, #12]
95e6: 6105 str r5, [r0, #16]
95e8: 6146 str r6, [r0, #20]
95ea: 6187 str r7, [r0, #24]
95ec: 4641 mov r1, r8
95ee: 61c1 str r1, [r0, #28]
95f0: 4649 mov r1, r9
95f2: 6201 str r1, [r0, #32]
95f4: 4651 mov r1, sl
95f6: 6241 str r1, [r0, #36] @ 0x24
95f8: 4659 mov r1, fp
95fa: 6281 str r1, [r0, #40] @ 0x28
95fc: 4669 mov r1, sp
95fe: 62c1 str r1, [r0, #44] @ 0x2c
9600: 4671 mov r1, lr
9602: 6081 str r1, [r0, #8]
9604: e7de b.n 95c4 <nlr_push_tail>
Signed-off-by: Jonathan Neuschäfer j.neuschaefer@gmx.net