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runtime: fix frame pointer loop on amd64

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This commit addresses a regression caused by commit
43f911b0b6 (CL 472195) which led to frame
pointer cycles, causing frame pointer unwinders (refer to CL 463835) to
encounter repetitive stack frames.

The issue occurs when mcall invokes fn on g0's stack. fn is expected not
to return but to continue g's execution through gogo(&g.sched). To
achieve this, g.sched must hold the sp, pc, and bp of mcall's caller. CL
472195 mistakenly altered g.sched.bp to store mcall's own bp, causing
gogo to resume execution with a bp value that points downwards into the
now non-existent mcall frame. This results in the next function call
executed by mcall's callee pushing a bp that points to itself on the
stack, creating a pointer loop.

Fix this by dereferencing bp before storing it in g.sched.bp to
reinstate the correct behavior. Although this problem could potentially
be resolved by reverting the mcall-related changes from CL 472195, doing
so would hide mcall's caller frame from async frame pointer unwinders
like Linux perf when unwinding during fn's execution.

Currently, there is no test coverage for frame pointers to validate
these changes. However, runtime/trace.TestTraceSymbolize at CL 463835
will add basic test coverage and can be used to validate this change.

Change-Id: Iad3c42908eeb1b0009fcb839d7fcfffe53d13326
Reviewed-on: https://go-review.googlesource.com/c/go/+/476235
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Felix Geisendörfer <felix.geisendoerfer@datadoghq.com>
This commit is contained in:
Felix Geisendörfer 2023-03-14 18:25:31 +01:00 committed by Michael Pratt
parent 8890c3a05f
commit b52f6d3721
1 changed files with 7 additions and 4 deletions
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11
src/runtime/asm_amd64.s
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@ -428,15 +428,18 @@ TEXT gogo<>(SB), NOSPLIT, $0
TEXT runtime·mcall<ABIInternal>(SB), NOSPLIT, $0-8
MOVQ AX, DX // DX = fn
// Save state in g->sched.
// The original frame pointer is stored in BP,
// which is useful for stack unwinding.
// Save state in g->sched. The caller's SP and PC are restored by gogo to
// resume execution in the caller's frame (implicit return). The caller's BP
// is also restored to support frame pointer unwinding.
MOVQ SP, BX // hide (SP) reads from vet
MOVQ 8(BX), BX // caller's PC
MOVQ BX, (g_sched+gobuf_pc)(R14)
LEAQ fn+0(FP), BX // caller's SP
MOVQ BX, (g_sched+gobuf_sp)(R14)
MOVQ BP, (g_sched+gobuf_bp)(R14)
// Get the caller's frame pointer by dereferencing BP. Storing BP as it is
// can cause a frame pointer cycle, see CL 476235.
MOVQ (BP), BX // caller's BP
MOVQ BX, (g_sched+gobuf_bp)(R14)
// switch to m->g0 & its stack, call fn
MOVQ g_m(R14), BX