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arch: arm: Use BL instead of B to jump to _PrepC

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The __reset vector is using the 'b' instruction to jump to _PrepC. 'b'
can only jump 2KB on Cortex-M0 platforms so this causes build failures
when _PrepC happens to be too far away from __reset.

To resolve this we use 'bl' instead as it can jump two thousand times
further[0].

This can also be resolved by porting the reset vector to C or by
placing the _PrepC function in a dedicated section that the linker
places next to __reset.

[0] http://infocenter.arm.com/help/topic/com.arm.doc.dui0489e/Cihfddaf.html

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
This commit is contained in:
Sebastian Bøe 2018-09-12 09:43:14 +02:00 committed by Anas Nashif
parent 1b80f00f56
commit 1765276000
1 changed files with 6 additions and 1 deletions
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7
arch/arm/core/cortex_m/reset.S
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@ -102,4 +102,9 @@ SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)
*/
isb
b _PrepC
/*
* 'bl' jumps the furthest of the branch instructions that are
* supported on all platforms. So it is used when jumping to _PrepC
* (even though we do not intend to return).
*/
bl _PrepC