proc: fix arm64 crosscall2 SP restore for cgo stacktraces - #4399
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proc: fix arm64 crosscall2 SP restore for cgo stacktraces#4399derekparker wants to merge 4 commits into
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crosscall2 does SUB $(8*24), RSP but never spills SP. Linux/arm64 was restoring SP from the saved frame pointer, which only works when C frames keep a frame pointer; with newer GCC (Ubuntu 24.04 CI) that omits them, TestCgoStacktrace skips C frames after a cgo callback. Loading *(SP+8*24) is also wrong (that slot is the caller's stack contents). Restore the caller SP as SP+8*24, matching what crosscall2's epilogue adds back.
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Apply the same SP+framesize restore used on arm64: crosscall2 adjusts SP but does not spill it, so loading from SP+N reads caller stack contents. Also correct ppc64le BP/LR slot offsets from the host ABI save macros, and re-enable TestCgoStacktrace on linux/ppc64le.
The arm64 crosscall2 SP restore fix applies to all GOOS via arm64_arch.go, so re-enable the previously skipped windows/arm64 cgo stacktrace test.
C frames on windows/arm64 use PE .pdata/.xdata from clang, not DWARF .debug_frame. Delve does not unwind via .pdata yet, so step 1 fails inside C before asmcgocall or crosscall2. That is unrelated to the arm64 crosscall2 SP restore this PR fixes.
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July 28, 2026 18:08
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crosscall2adjusts SP (e.g.SUB $(8*24), RSPon arm64) but never spills it. Delve was either restoring SP from the saved frame pointer (linux/arm64) or loading*(SP+N)(other LR arches). Both are wrong: the FP fallback only works when C keeps a frame pointer, and*(SP+N)is the caller's stack contents.After the TeamCity Ubuntu 20.04 -> 24.04 bump (newer GCC), cgo-compiled C more often omits frame pointers, so
TestCgoStacktracefailed on linux/arm64 at the C→Go callback step.Restore the caller SP as
SP + framesize, matching what each arch'scrosscall2epilogue adds back. Applied on arm64, riscv64, loong64, and ppc64le (with corrected ppc64le BP/LR save slots). Re-enableTestCgoStacktraceon linux/ppc64le.darwin/arm64 shares the arm64 path and gets the same correct restore.