rename the types of core peripherals to UPPERCASE #41
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japaric
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adamgreig
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Jan 12, 2022
This is one possible solution to the stack overflow problem described in #34. This approach uses a linker wrapper, called [swap-ld], to generate the desired memory layout. See #34 for a description of the desired memory layout and #41 for a description of how `swap-ld` works. The observable effects of this change in cortex-m programs are: - the `_sbss` symbol is now override-able. - there is now a `.stack` linker section that denotes the span of the call stack. `.stack` won't be loaded into the program; it just exists for informative purposes (`swap-ld` uses this information). Given the following program: ``` rust fn main() { static mut X: u32 = 0; static mut Y: u32 = 1; loop { unsafe { ptr::write_volatile(&mut X, X + 1); ptr::write_volatile(&mut Y, Y + 1); } } } ``` If you link this program using the `arm-none-eabi-ld` linker, which is the cortex-m-quickstart default, you'll get the following memory layout: ``` console $ console section size addr .vector_table 0x130 0x8000000 .text 0x94 0x8000130 .rodata 0x0 0x80001c4 .stack 0x5000 0x20000000 .bss 0x4 0x20000000 .data 0x4 0x20000004 ``` Note how the space reserved for the stack (depicted by the `.stack` linker section) overlaps with the space where .bss and .data reside. If you, instead, link this program using `swap-ld` you'll get the following memory layout: ``` console $ arm-none-eabi-size -Ax app section size addr .vector_table 0x130 0x8000000 .text 0x94 0x8000130 .rodata 0x0 0x80001c4 .stack 0x4ff8 0x20000000 .bss 0x4 0x20004ff8 .data 0x4 0x20004ffc ``` Note that no overlap exists in this case and that the call stack size has reduced to accommodate the .bss and .data sections. Unlike #41 the addresses of static variables is now correct: ``` console $ arm-none-eabi-objdump -CD app Disassembly of section .vector_table: 08000000 <_svector_table>: 8000000: 20004ff8 strdcs r4, [r0], -r8 ; initial Stack Pointer 08000004 <cortex_m_rt::RESET_VECTOR>: 8000004: 08000131 stmdaeq r0, {r0, r4, r5, r8} 08000008 <EXCEPTIONS>: 8000008: 080001bd stmdaeq r0, {r0, r2, r3, r4, r5, r7, r8} (..) Disassembly of section .stack: 20000000 <.stack>: ... Disassembly of section .bss: 20004ff8 <cortex_m_quickstart::main::X>: 20004ff8: 00000000 andeq r0, r0, r0 Disassembly of section .data: 20004ffc <_sdata>: 20004ffc: 00000001 andeq r0, r0, r1 ``` closes #34 [swap-ld]: https://github.com/japaric/swap-ld
reitermarkus
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May 4, 2022
This is one possible solution to the stack overflow problem described in rust-embedded#34. This approach uses a linker wrapper, called [swap-ld], to generate the desired memory layout. See rust-embedded#34 for a description of the desired memory layout and rust-embedded#41 for a description of how `swap-ld` works. The observable effects of this change in cortex-m programs are: - the `_sbss` symbol is now override-able. - there is now a `.stack` linker section that denotes the span of the call stack. `.stack` won't be loaded into the program; it just exists for informative purposes (`swap-ld` uses this information). Given the following program: ``` rust fn main() { static mut X: u32 = 0; static mut Y: u32 = 1; loop { unsafe { ptr::write_volatile(&mut X, X + 1); ptr::write_volatile(&mut Y, Y + 1); } } } ``` If you link this program using the `arm-none-eabi-ld` linker, which is the cortex-m-quickstart default, you'll get the following memory layout: ``` console $ console section size addr .vector_table 0x130 0x8000000 .text 0x94 0x8000130 .rodata 0x0 0x80001c4 .stack 0x5000 0x20000000 .bss 0x4 0x20000000 .data 0x4 0x20000004 ``` Note how the space reserved for the stack (depicted by the `.stack` linker section) overlaps with the space where .bss and .data reside. If you, instead, link this program using `swap-ld` you'll get the following memory layout: ``` console $ arm-none-eabi-size -Ax app section size addr .vector_table 0x130 0x8000000 .text 0x94 0x8000130 .rodata 0x0 0x80001c4 .stack 0x4ff8 0x20000000 .bss 0x4 0x20004ff8 .data 0x4 0x20004ffc ``` Note that no overlap exists in this case and that the call stack size has reduced to accommodate the .bss and .data sections. Unlike rust-embedded#41 the addresses of static variables is now correct: ``` console $ arm-none-eabi-objdump -CD app Disassembly of section .vector_table: 08000000 <_svector_table>: 8000000: 20004ff8 strdcs r4, [r0], -r8 ; initial Stack Pointer 08000004 <cortex_m_rt::RESET_VECTOR>: 8000004: 08000131 stmdaeq r0, {r0, r4, r5, r8} 08000008 <EXCEPTIONS>: 8000008: 080001bd stmdaeq r0, {r0, r2, r3, r4, r5, r7, r8} (..) Disassembly of section .stack: 20000000 <.stack>: ... Disassembly of section .bss: 20004ff8 <cortex_m_quickstart::main::X>: 20004ff8: 00000000 andeq r0, r0, r0 Disassembly of section .data: 20004ffc <_sdata>: 20004ffc: 00000001 andeq r0, r0, r1 ``` closes rust-embedded#34 [swap-ld]: https://github.com/japaric/swap-ld
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to match the changes in svd2rust.
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