From 6afc21a7c1a73ead3e60aa09ceeb343321f43ba4 Mon Sep 17 00:00:00 2001 From: Jorge Aparicio Date: Wed, 2 Sep 2020 15:52:17 +0200 Subject: [PATCH] [ARMv6-M] initialize the LR register the ARMv6-M Architecture Reference Manual (ARM DDI 0419D) indicates in section B1.5.5 "Reset behavior" that the LR (Link Register) starts in an unknown state when the Reset handler is taken and that its "Value must be initialised by software" So this PR does that: it initializes the LR register to 0xFFFF_FFFF (-1) first thing in the Reset handler (only for v6). The manual doesn't say which value to use so I decided to use the value used by the ARMv7-M (v7 sets LR to 0xFFFF_FFFF before invoking the Reset handler; see its Architecture Manual for details). The values of LR (these are pushed onto the stack in function preludes) are used to unwind the stack (e.g. GDB's `backtrace` or a future `cortex_m_panic_unwind` handler). Having the initial stack frame use a known value on all Cortex-M variants makes it easier to implement `panic_unwind` and avoids virtual unwinders like GDB `backtrace` trying to unwind beyond the `Reset` handler Note that this implementation uses a trampoline that runs before `Reset` to set LR on v6. This is required because the prelude of the `Reset` routine will push LR onto the stack; we want that LR value to be -1. Calling `register::lr::write` from `Reset` would perform the write after LR has been pushed onto the stack and that's too late --- asm.s | 14 ++++++++++++++ bin/thumbv6m-none-eabi.a | Bin 940 -> 1212 bytes bin/thumbv7em-none-eabi.a | Bin 940 -> 1172 bytes bin/thumbv7em-none-eabihf.a | Bin 940 -> 1172 bytes bin/thumbv7m-none-eabi.a | Bin 940 -> 1172 bytes bin/thumbv8m.base-none-eabi.a | Bin 944 -> 1216 bytes bin/thumbv8m.main-none-eabi.a | Bin 944 -> 1176 bytes bin/thumbv8m.main-none-eabihf.a | Bin 944 -> 1176 bytes link.x.in | 4 ++++ src/lib.rs | 11 +++++++++++ 10 files changed, 29 insertions(+) diff --git a/asm.s b/asm.s index 50a3fa56..c1953c67 100644 --- a/asm.s +++ b/asm.s @@ -17,3 +17,17 @@ HardFaultTrampoline: 0: mrs r0, PSP b HardFault + + # ARMv6-M leaves LR in an unknown state on Reset + # this trampoline sets LR before it's pushed onto the stack by Reset + .section .PreResetTrampoline, "ax" + .global PreResetTrampoline + # .type and .thumb_func are both required; otherwise its Thumb bit does not + # get set and an invalid vector table is generated + .type PreResetTrampoline,%function + .thumb_func +PreResetTrampoline: + # set LR to the initial value used by the ARMv7-M (0xFFFF_FFFF) + ldr r0,=0xffffffff + mov lr,r0 + b Reset diff --git a/bin/thumbv6m-none-eabi.a b/bin/thumbv6m-none-eabi.a index 6a6a54702f4eb87c5ea0161a92a9e0bdb4ca22cb..28e2ec7fe8c997a7c9eba426a57b862dff738b9e 100644 GIT binary patch literal 1212 zcma)6&1w@-6#k|Y(FO`|5XQ<}|k``?OYj{ZbwJ6#y&5 zQ^BsW!;U!_y8~+`v*~#BCB{b^@5f2(t8h5AE0vgf{aIc-R2C7)YtW&6$-mUz+x-OmFTwYz5NrUcr=jIalP1t=* zXA_&j2*E=M-ul$+p;%q*mHpIdMxTUtDg$9Uin&KfjSnFT3lRn1Oz+}?y~qeqtB{>b zdh{%!3Q@u;xi-DdXt|og0}4-xb9)inY9tpsHXJsFShmVr-Lj>oOJ;bLcto!(Z)Uf15MZ5dG$T(+5gA*4gtoGj^ z^O1SzjI(z$56_+xP|y8zqlprKVOnjRgE?7wRBs!U` zpwxR$^zYH-S$3fyegb<$Ki_u-NxbN!7tQyXGVd@WOW}a@NiGZ1`wG`yMK1xri1K4t fBT7E)S7$;M`V8C=AqUMT-=FXIgNBJZk*nVyfNO;M delta 239 zcmdnPxrTj$g@}=b0u&^0F)%PN0&&8`0Fj9m1}x?lCJGbRXlOKm1Q{4uO~8}}0~Z4) zLxCHMB8L;x#rK~%8vZ?h|Ctj=PUc|jQDFfpf~aR;5Mp3qkN|6f5CR}drGx=!{$zb7 zE+Cf&D3HbhQVF6bXEAw9KE?D(QvzrLNHIGQgA4>=pehDeAZBJ@C;(Dm;4xX3MV&VV i$esYiAQkMB6IrBLzW`ZElN(u-Sv7zrg-&*476t&qcqLW< diff --git a/bin/thumbv7em-none-eabi.a b/bin/thumbv7em-none-eabi.a index 51d9aef4767948e5b33318aa4b2f00d22b811e92..8d9a9eb85014fe2bafdb8500201cefff8406ab8f 100644 GIT binary patch delta 390 zcmZ3(K816Fg}tef0u&^0F)%PN0dWNgdn6X6xFwe6l!O!|<`(4VWagzZ1QewPr52|m z3r&nSWVW<4nmAcg7_66pfz<@4oq<7vfro*6;(1Xv{}2BS+T12S>XT;#OTY*=7z0c* zGjL4KXH*na0`g$$gc#TuOeZ%o8X91+80-)Rpd}0pX+VbyL1~bwX*`n;F?w(prRL~C zHBSD^_+7UGXs!TIniGgwpqK+ldjc`YN|=K@fNYM*7ny`DU4bl+Y6l<&fexTDkPeU- zNHxe55I+`(nHd-gfD{-6OqOL<=gk4KF90zpSUD#LGE1}C0QFl>E@W0_od9IzPHtop F1^|nBK{fyY delta 212 zcmbQjxrTj$g@}=b0u&^0F)%PN0&&8`0Fj9m2F&IbCKFd{sx^Sb7#LVhz?2397Xv3l zfg6h=hZEDq_n$c${yl&HnX_Rs6Jy`x4U7ttKQJl@Ffi}{6{m49FbIL^$xcijlNT|) z(v<+31(aoA2Vxc|2C8Ck1!86fh5{f31|C3CX0ju*@MIYl0p1iKZvqg5RI*RDWRYh5 T0%R$H<#SjBST%sAhJtti_?;w{ diff --git a/bin/thumbv7em-none-eabihf.a b/bin/thumbv7em-none-eabihf.a index 51d9aef4767948e5b33318aa4b2f00d22b811e92..8d9a9eb85014fe2bafdb8500201cefff8406ab8f 100644 GIT binary patch delta 390 zcmZ3(K816Fg}tef0u&^0F)%PN0dWNgdn6X6xFwe6l!O!|<`(4VWagzZ1QewPr52|m z3r&nSWVW<4nmAcg7_66pfz<@4oq<7vfro*6;(1Xv{}2BS+T12S>XT;#OTY*=7z0c* zGjL4KXH*na0`g$$gc#TuOeZ%o8X91+80-)Rpd}0pX+VbyL1~bwX*`n;F?w(prRL~C zHBSD^_+7UGXs!TIniGgwpqK+ldjc`YN|=K@fNYM*7ny`DU4bl+Y6l<&fexTDkPeU- zNHxe55I+`(nHd-gfD{-6OqOL<=gk4KF90zpSUD#LGE1}C0QFl>E@W0_od9IzPHtop F1^|nBK{fyY delta 212 zcmbQjxrTj$g@}=b0u&^0F)%PN0&&8`0Fj9m2F&IbCKFd{sx^Sb7#LVhz?2397Xv3l zfg6h=hZEDq_n$c${yl&HnX_Rs6Jy`x4U7ttKQJl@Ffi}{6{m49FbIL^$xcijlNT|) z(v<+31(aoA2Vxc|2C8Ck1!86fh5{f31|C3CX0ju*@MIYl0p1iKZvqg5RI*RDWRYh5 T0%R$H<#SjBST%sAhJtti_?;w{ diff --git a/bin/thumbv7m-none-eabi.a b/bin/thumbv7m-none-eabi.a index dc37fbf0404c2a27212652a1fb72b009e3b2d193..504c0c873afa1145924be34353a1f82bc173c641 100644 GIT binary patch delta 390 zcmZ3(K816Fg}tef0u&^0F)%PN0dWNgdn6X6xFwe6l!O!|<`(4VWagzZ1QewPr52|m z3r&nSWVW<4nmAcg7_66pfz<@4oq<7vfro*6;(1Xv{}2BS+T12S>XT;#OTY*=7z0c* zGjL4KXH*na0`g$$gc#TuOeZ%o8X91+80-)Rpd}0pX+VbyL1~bwX*`n;F?w(prRL~C zHBSD^_+7UGXs!TIniGgwpqK+ldjc`YN|=K@fNYM*7ny`DU4bl+Y6l<&fexTDkPeU- zNHxe55I+`(nHd-gfD{-6OqOL<=gk4KF90zpSUD#LGE1}C0QFl>E@W0_od9IzPHtop F1^|nBK{fyY delta 212 zcmbQjxrTj$g@}=b0u&^0F)%PN0&&8`0Fj9m2F&IbCKFd{sx^Sb7#LVhz?2397Xv3l zfg6h=hZEDq_n$c${yl&HnX_Rs6Jy`x4U7ttKQJl@Ffi}{6{m49FbIL^$xcijlNT|) z(v<+31(aoA2Vxc|2C8Ck1!86fh5{f31|C3Cda@(4@MIYl0p1iKZvqg5RI*RDWRYh5 T0%R$H<#SjBST%sAhJtti_-Z7T diff --git a/bin/thumbv8m.base-none-eabi.a b/bin/thumbv8m.base-none-eabi.a index dda8dcc75a9d831309f2498525f6d5ace57c30eb..067ead6ec349448ccc94084201477217d43307e4 100644 GIT binary patch literal 1216 zcma)6K}%af5dNMojY*VZr9Jh~1T6Jnwy8$(P^1wOQfQ!9uLU>eiGjp~eJkjxJ@uFL zC-m4q(O==wf_K|*-g}#DLZls-nVp$$X7+&qsJTpD}vRvNXc7T%- zfF<&ka9f*ROJ5G`vC+fvXwbii@X0;#;)XWYMg(N@kIkuZLE5sjW%%xjXSeSg4-18mb$|P$n9vNjL97C4mL6N;Qr;N?U9C-AfzA z?DpRz^O1SE8K-Y&nw~x>ppxO-M(1&E=C6p8{rn48%j)@kpVH^Z_1&VQNPd?EzO#|+ zQG7C6Vd?jt?0-j_w(P=@;DnlFzupffNxt~xF0S5Zp7{-9s)UXy%jq$Z(o0CRyQ|oi l{F^L4hZVBabN6*Kp$k1G9>^ghSMLdJANP}ip#xDn++SDWh9Cd{ delta 284 zcmX@Wxq*Fxg@}=b0u&^0F)%PN0&&9Rg-jw7D-2l7Ei4o!uF=qF0f{m&u$q7=4F)a- zPKE+E7DWyxri<@Cb2R*W{{Ay3ketlHI6;L4s0gB-fkB9Yg+T(W2|@^fD3uZhkOfj6 ziA5=HiKRIuKrtR5PU8S+0MV24m^>z*V|t}212hPvhaHGP=7KO#6@x1fGczz004Xr= sm~6blhm<6Plfq~ToOldIiFmO*iFUscs;lDwf+r&qc{ delta 215 zcmbQixq*Fxg@}=b0u&^0F)%PN0&&8`0Fj9m2F&Ib786%%sP-U|`?@Do*2IU=RY+liip+CNE=p zr6~h63nklAHX>u%! 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SvV;!Mq);Fa1|W`PU;qGQhawCB diff --git a/link.x.in b/link.x.in index 30d4af10..5a277e27 100644 --- a/link.x.in +++ b/link.x.in @@ -85,6 +85,10 @@ SECTIONS /* ### .text */ .text _stext : { + /* place these 2 close to each other or the `b` instruction will fail to link */ + *(.PreResetTrampoline); + *(.Reset); + *(.text .text.*); *(.HardFaultTrampoline); *(.HardFault.*); diff --git a/src/lib.rs b/src/lib.rs index 85d94965..1f95dc2d 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -482,9 +482,17 @@ pub fn heap_start() -> *mut u32 { #[doc(hidden)] #[link_section = ".vector_table.reset_vector"] #[no_mangle] +#[cfg(not(armv6m))] pub static __RESET_VECTOR: unsafe extern "C" fn() -> ! = Reset; #[doc(hidden)] +#[link_section = ".vector_table.reset_vector"] +#[no_mangle] +#[cfg(armv6m)] +pub static __RESET_VECTOR: unsafe extern "C" fn() -> ! = PreResetTrampoline; + +#[doc(hidden)] +#[link_section = ".Reset"] #[no_mangle] pub unsafe extern "C" fn Reset() -> ! { extern "C" { @@ -600,6 +608,9 @@ pub enum Exception { } extern "C" { + #[cfg(armv6m)] + fn PreResetTrampoline() -> !; + fn NonMaskableInt(); fn HardFaultTrampoline();