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Add fcontext support for arm64e (AAPCS/Mach-O) #345

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Add fcontext support for arm64e (AAPCS/Mach-O) #345

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15 changes: 15 additions & 0 deletions src/asm/jump_arm64_aapcs_macho_gas.S
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,15 @@ _jump_fcontext:
stp fp, lr, [sp, #0x90]

; save LR as PC
#if defined(__arm64e__)
; signed with the address of its slot
mov x16, lr
add x17, sp, #0xa0
pacia x16, x17
str x16, [sp, #0xa0]
#else
str lr, [sp, #0xa0]
#endif

; store RSP (pointing to context-data) in X0
mov x4, sp
Expand Down Expand Up @@ -103,8 +111,15 @@ _jump_fcontext:

; load pc
ldr x4, [sp, #0xa0]
#if defined(__arm64e__)
add x17, sp, #0xa0
#endif

; restore stack from GP + FPU
add sp, sp, #0xb0

#if defined(__arm64e__)
braa x4, x17
#else
ret x4
#endif
18 changes: 18 additions & 0 deletions src/asm/make_arm64_aapcs_macho_gas.S
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Expand Up @@ -70,7 +70,25 @@ _make_fcontext:

; third arg of make_fcontext() == address of context-function
; store address as a PC to jump in
#if defined(__arm64e__)
; authenticate the C function pointer (IA, zero discriminator) and sign it
; with the address of its slot, as jump_fcontext signs a saved PC
mov x16, x2
autiza x16
; trap if authentication failed rather than re-sign a forged pointer,
; as clang does for arm64e
mov x17, x16
xpaci x17
cmp x16, x17
b.eq 1f
brk #0xc470
1:
add x17, x0, #0xa0
pacia x16, x17
str x16, [x0, #0xa0]
#else
str x2, [x0, #0xa0]
#endif

adr x1, finish

Expand Down
13 changes: 13 additions & 0 deletions src/asm/ontop_arm64_aapcs_macho_gas.S
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Expand Up @@ -74,7 +74,15 @@ _ontop_fcontext:
stp x29, x30, [sp, #0x90]

; save LR as PC
#if defined(__arm64e__)
; signed with the address of its slot, which jump_fcontext authenticates
mov x16, x30
add x17, sp, #0xa0
pacia x16, x17
str x16, [sp, #0xa0]
#else
str x30, [sp, #0xa0]
#endif

; store RSP (pointing to context-data) in X5
mov x4, sp
Expand Down Expand Up @@ -106,4 +114,9 @@ _ontop_fcontext:
add sp, sp, #0xb0

; jump to ontop-function
#if defined(__arm64e__)
; a C function pointer: IA, zero discriminator
braaz x2
#else
ret x2
#endif