From: Nick Ripley <nick.ripley@datadoghq.com>
Date: Mon, 17 Nov 2025 16:47:20 +0000 (-0500)
Subject: runtime: clear frame pointer at thread entry points
X-Git-Tag: go1.26rc1~256
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=eda2e8c683;p=gostls13.git

runtime: clear frame pointer at thread entry points

There are a few places in the runtime where new threads enter Go code
with a possibly invalid frame pointer. mstart is the entry point for new
Ms, and rt0_go is the entrypoint for the program. As we try to introduce
frame pointer unwinding in more places (e.g. for heap profiling in CL
540476 or for execution trace events on the system stack in CL 593835),
we see these functions on the stack. We need to ensure that they have
valid frame pointers. These functions are both considered the "top"
(first) frame frame of the call stack, so this CL sets the frame pointer
register to 0 in these functions.

Updates #63630

Change-Id: I6a6a6964a9ebc6f68ba23d2616e5fb6f19677f97
Reviewed-on: https://go-review.googlesource.com/c/go/+/721020
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
---

diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index a4c6c53a90..f4244f6e06 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -181,6 +181,14 @@ TEXT runtime·rt0_go(SB),NOSPLIT|NOFRAME|TOPFRAME,$0
 	MOVQ	AX, 24(SP)
 	MOVQ	BX, 32(SP)
 
+	// This is typically the entry point for Go programs.
+	// Call stack unwinding must not proceed past this frame.
+	// Set the frame pointer register to 0 so that frame pointer-based unwinders
+	// (which don't use debug info for performance reasons)
+	// won't attempt to unwind past this function.
+	// See go.dev/issue/63630
+	MOVQ	$0, BP
+
 	// create istack out of the given (operating system) stack.
 	// _cgo_init may update stackguard.
 	MOVQ	$runtime·g0(SB), DI
@@ -408,6 +416,13 @@ TEXT runtime·asminit(SB),NOSPLIT,$0-0
 	RET
 
 TEXT runtime·mstart(SB),NOSPLIT|TOPFRAME|NOFRAME,$0
+	// This is the root frame of new Go-created OS threads.
+	// Call stack unwinding must not proceed past this frame.
+	// Set the frame pointer register to 0 so that frame pointer-based unwinders
+	// (which don't use debug info for performance reasons)
+	// won't attempt to unwind past this function.
+	// See go.dev/issue/63630
+	MOVD	$0, BP
 	CALL	runtime·mstart0(SB)
 	RET // not reached
 
diff --git a/src/runtime/asm_arm64.s b/src/runtime/asm_arm64.s
index 902a7066aa..01f2690f4e 100644
--- a/src/runtime/asm_arm64.s
+++ b/src/runtime/asm_arm64.s
@@ -109,6 +109,14 @@ TEXT runtime·rt0_go(SB),NOSPLIT|TOPFRAME,$0
 	MOVW	R0, 8(RSP) // argc
 	MOVD	R1, 16(RSP) // argv
 
+	// This is typically the entry point for Go programs.
+	// Call stack unwinding must not proceed past this frame.
+	// Set the frame pointer register to 0 so that frame pointer-based unwinders
+	// (which don't use debug info for performance reasons)
+	// won't attempt to unwind past this function.
+	// See go.dev/issue/63630
+	MOVD	$0, R29
+
 #ifdef TLS_darwin
 	// Initialize TLS.
 	MOVD	ZR, g // clear g, make sure it's not junk.
@@ -248,6 +256,13 @@ TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0
 	RET
 
 TEXT runtime·mstart(SB),NOSPLIT|TOPFRAME,$0
+	// This is the root frame of new Go-created OS threads.
+	// Call stack unwinding must not proceed past this frame.
+	// Set the frame pointer register to 0 so that frame pointer-based unwinders
+	// (which don't use debug info for performance reasons)
+	// won't attempt to unwind past this function.
+	// See go.dev/issue/63630
+	MOVD	$0, R29
 	BL	runtime·mstart0(SB)
 	RET // not reached