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py/asmthumb: Fix PC relative load by sign extending the constant.

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PC relative offsets can be negative, in which case the movw result must be
sign extended.

Signed-off-by: Damien George <damien@micropython.org>
This commit is contained in:
Damien George 2022-05-19 15:05:32 +10:00
parent c70f96f1c5
commit 56f2d3c2e5
1 changed files with 2 additions and 1 deletions
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py/asmthumb.c
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@ -430,8 +430,9 @@ void asm_thumb_mov_reg_pcrel(asm_thumb_t *as, uint rlo_dest, uint label) {
mp_int_t rel = dest - as->base.code_offset;
rel |= 1; // to stay in Thumb state when jumping to this address
#if MICROPY_EMIT_THUMB_ARMV7M
rel -= 4 + 4; // adjust for mov_reg_i16 and then PC+4 prefetch of add_reg_reg
rel -= 6 + 4; // adjust for mov_reg_i16, sxth_rlo_rlo and then PC+4 prefetch of add_reg_reg
asm_thumb_mov_reg_i16(as, ASM_THUMB_OP_MOVW, rlo_dest, rel); // 4 bytes
asm_thumb_sxth_rlo_rlo(as, rlo_dest, rlo_dest); // 2 bytes
#else
rel -= 8 + 4; // adjust for four instructions and then PC+4 prefetch of add_reg_reg
// 6 bytes