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cortex-m-rt: ensure the stack is 8-byte aligned. #463

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cortex-m-rt: ensure the stack is 8-byte aligned. #463

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cortex-m-rt: ensure the stack is 8-byte aligned.
Dirbaio Feb 11, 2023
6681bc7
Update cortex-m-rt/src/lib.rs
Dirbaio Feb 13, 2023
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8 changes: 5 additions & 3 deletions cortex-m-rt/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -573,10 +573,12 @@ cfg_global_asm! {
isb",

// Push `lr` to the stack for debuggers, to prevent them unwinding past Reset.
// See https://sourceware.org/binutils/docs/as/CFI-directives.html.
// Push a dummy `r4` (which is always 0xFFFF_FFFF) to ensure the stack stays 8-byte aligned.
// For CFI information, see https://sourceware.org/binutils/docs/as/CFI-directives.html.
// For 8 byte alignment, see https://github.com/ARM-software/abi-aa/blob/edd7460d87493fff124b8b5713acf71ffc06ee91/aapcs32/aapcs32.rst#6212stack-constraints-at-a-public-interface.
".cfi_def_cfa sp, 0
push {{lr}}
.cfi_offset lr, 0",
push {{r4, lr}}
.cfi_offset lr, 4",

// Jump to user main function.
// `bl` is used for the extended range, but the user main function should not return,
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