[asd1192698984]

fix(arm64): avoid clobbering R10 (11th argument slot) in the stub trampoline

What

Fix a SIGBUS on arm64 (darwin/arm64 & linux/arm64) caused by the stub trampoline clobbering register R10, which holds the 11th argument slot.

Why

In jmp_arm64.go, buildJmpDirective uses x10 as a temporary register:

LDR x10, [x26]
BR  x10

In Go's arm64 ABI, R0–R15 are the integer argument/result registers, so R10 is the 11th argument slot. Moreover, struct arguments are flattened field-by-field, so a signature like func Parse(in SomeBigStruct, out any) can easily put out's data word in R10.

When the target function is stubbed, LDR x10, [x26] overwrites the caller's 11th argument slot with the mock's own code address. If the mock dereferences or writes through that argument (e.g. *out.(*T) = ...), it writes into the mock's read-only text segment — SIGBUS on darwin/arm64 (W^X), SIGSEGV on linux/arm64.

Fix

Use x17 (the platform-reserved temp register REGRT2, never used to pass arguments) instead of x10:

- res = append(res, []byte{0x4A, 0x03, 0x40, 0xF9}...) // LDR x10, [x26]
- res = append(res, []byte{0x40, 0x01, 0x1F, 0xD6}...) // BR   x10
+ res = append(res, []byte{0x51, 0x03, 0x40, 0xF9}...) // LDR x17, [x26]
+ res = append(res, []byte{0x20, 0x02, 0x1F, 0xD6}...) // BR   x17

MOVZ/MOVK x26 is unchanged (x26 is callee-saved and not on the argument path).

Test

Added TestApplyFuncArm64R10: stubs a function whose signature puts an any argument's data word in R10, and the mock writes through it. On unpatched arm64 this writes to the mock's own text segment (SIGBUS); with the fix it passes.

Scope

• Fixes darwin/arm64 and linux/arm64 (shared jmp_arm64.go).
• amd64 / 386 / loong64 / riscv64 use their own jmp_*.go with non-argument temp registers — unaffected.

Related: #181