Skip to content

cortex-m-rt: Remove LR push, to ensure the stack is 8-byte aligned. #467

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Feb 14, 2023
Merged

cortex-m-rt: Remove LR push, to ensure the stack is 8-byte aligned. #467

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
16 changes: 1 addition & 15 deletions cortex-m-rt/src/lib.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -507,12 +507,6 @@ cfg_global_asm! {
".cfi_startproc
Reset:",

// Ensure LR is loaded with 0xFFFF_FFFF at startup to help debuggers find the first call frame.
// On ARMv6-M LR is not initialised at all, while other platforms should initialise it.
"movs r4, #0
mvns r4, r4
mov lr, r4",

// If enabled, initialise the SP. This is normally initialised by the CPU itself or by a
// bootloader, but some debuggers fail to set it when resetting the target, leading to
// stack corruptions.
Expand All @@ -533,9 +527,7 @@ cfg_global_asm! {
// Run user pre-init code which must be executed immediately after startup, before the
// potentially time-consuming memory initialisation takes place.
// Example use cases include disabling default watchdogs or enabling RAM.
// Reload LR after returning from pre-init (r4 is preserved by subroutines).
"bl __pre_init
mov lr, r4",
"bl __pre_init",

// Initialise .bss memory. `__sbss` and `__ebss` come from the linker script.
"ldr r0, =__sbss
Expand Down Expand Up @@ -572,12 +564,6 @@ cfg_global_asm! {
dsb
isb",

// Push `lr` to the stack for debuggers, to prevent them unwinding past Reset.
// See https://sourceware.org/binutils/docs/as/CFI-directives.html.
".cfi_def_cfa sp, 0
push {{lr}}
.cfi_offset lr, 0",

// Jump to user main function.
// `bl` is used for the extended range, but the user main function should not return,
// so trap on any unexpected return.
Expand Down