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runtime: add valgrind instrumentation

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Add build tag gated Valgrind annotations to the runtime which let it
understand how the runtime manages memory. This allows for Go binaries
to be run under Valgrind without emitting spurious errors.

Instead of adding the Valgrind headers to the tree, and using cgo to
call the various Valgrind client request macros, we just add an assembly
function which emits the necessary instructions to trigger client
requests.

In particular we add instrumentation of the memory allocator, using a
two-level mempool structure (as described in the Valgrind manual [0]).
We also add annotations which allow Valgrind to track which memory we
use for stacks, which seems necessary to let it properly function.

We describe the memory model to Valgrind as follows: we treat heap
arenas as a "pool" created with VALGRIND_CREATE_MEMPOOL_EXT (so that we
can use VALGRIND_MEMPOOL_METAPOOL and VALGRIND_MEMPOOL_AUTO_FREE).
Within the pool we treat spans as "superblocks", annotated with
VALGRIND_MEMPOOL_ALLOC. We then allocate individual objects within spans
with VALGRIND_MALLOCLIKE_BLOCK.

It should be noted that running binaries under Valgrind can be _quite
slow_, and certain operations, such as running the GC, can be _very
slow_. It is recommended to run programs with GOGC=off. Additionally,
async preemption should be turned off, since it'll cause strange
behavior (GODEBUG=asyncpreemptoff=1).

Running Valgrind with --leak-check=yes will result in some errors
resulting from some things not being marked fully free'd. These likely
need more annotations to rectify, but for now it is recommended to run
with --leak-check=off.

Updates #73602

[0] https://valgrind.org/docs/manual/mc-manual.html#mc-manual.mempools

Change-Id: I71b26c47d7084de71ef1e03947ef6b1cc6d38301
Reviewed-on: https://go-review.googlesource.com/c/go/+/674077
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Roland Shoemaker 2025-03-22 00:58:55 +00:00
parent 2a5ac1a993
commit 40b19b56a9
15 changed files with 364 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

48
src/runtime/stack.go
View file

@ -211,6 +211,13 @@ func stackpoolalloc(order uint8) gclinkptr {
s.elemsize = fixedStack << order
for i := uintptr(0); i < _StackCacheSize; i += s.elemsize {
x := gclinkptr(s.base() + i)
if valgrindenabled {
// The address of x.ptr() becomes the base of stacks. We need to
// mark it allocated here and in stackfree and stackpoolfree, and free'd in
// stackalloc in order to avoid overlapping allocations and
// uninitialized memory errors in valgrind.
valgrindMalloc(unsafe.Pointer(x.ptr()), unsafe.Sizeof(x.ptr()))
}
x.ptr().next = s.manualFreeList
s.manualFreeList = x
}
@ -388,6 +395,12 @@ func stackalloc(n uint32) stack {
c.stackcache[order].list = x.ptr().next
c.stackcache[order].size -= uintptr(n)
}
if valgrindenabled {
// We're about to allocate the stack region starting at x.ptr().
// To prevent valgrind from complaining about overlapping allocations,
// we need to mark the (previously allocated) memory as free'd.
valgrindFree(unsafe.Pointer(x.ptr()))
}
v = unsafe.Pointer(x)
} else {
var s *mspan
@ -432,6 +445,9 @@ func stackalloc(n uint32) stack {
if asanenabled {
asanunpoison(v, uintptr(n))
}
if valgrindenabled {
valgrindMalloc(v, uintptr(n))
}
if stackDebug >= 1 {
print(" allocated ", v, "\n")
}
@ -479,6 +495,9 @@ func stackfree(stk stack) {
if asanenabled {
asanpoison(v, n)
}
if valgrindenabled {
valgrindFree(v)
}
if n < fixedStack<<_NumStackOrders && n < _StackCacheSize {
order := uint8(0)
n2 := n
@ -489,6 +508,11 @@ func stackfree(stk stack) {
x := gclinkptr(v)
if stackNoCache != 0 || gp.m.p == 0 || gp.m.preemptoff != "" {
lock(&stackpool[order].item.mu)
if valgrindenabled {
// x.ptr() is the head of the list of free stacks, and will be used
// when allocating a new stack, so it has to be marked allocated.
valgrindMalloc(unsafe.Pointer(x.ptr()), unsafe.Sizeof(x.ptr()))
}
stackpoolfree(x, order)
unlock(&stackpool[order].item.mu)
} else {
@ -496,6 +520,12 @@ func stackfree(stk stack) {
if c.stackcache[order].size >= _StackCacheSize {
stackcacherelease(c, order)
}
if valgrindenabled {
// x.ptr() is the head of the list of free stacks, and will
// be used when allocating a new stack, so it has to be
// marked allocated.
valgrindMalloc(unsafe.Pointer(x.ptr()), unsafe.Sizeof(x.ptr()))
}
x.ptr().next = c.stackcache[order].list
c.stackcache[order].list = x
c.stackcache[order].size += n
@ -583,6 +613,16 @@ func adjustpointer(adjinfo *adjustinfo, vpp unsafe.Pointer) {
if stackDebug >= 4 {
print(" ", pp, ":", hex(p), "\n")
}
if valgrindenabled {
// p is a pointer on a stack, it is inherently initialized, as
// everything on the stack is, but valgrind for _some unknown reason_
// sometimes thinks it's uninitialized, and flags operations on p below
// as uninitialized. We just initialize it if valgrind thinks its
// uninitialized.
//
// See go.dev/issues/73801.
valgrindMakeMemDefined(unsafe.Pointer(&p), unsafe.Sizeof(&p))
}
if adjinfo.old.lo <= p && p < adjinfo.old.hi {
*pp = p + adjinfo.delta
if stackDebug >= 3 {
@ -936,6 +976,14 @@ func copystack(gp *g, newsize uintptr) {
adjustframe(&u.frame, &adjinfo)
}
if valgrindenabled {
if gp.valgrindStackID == 0 {
gp.valgrindStackID = valgrindRegisterStack(unsafe.Pointer(new.lo), unsafe.Pointer(new.hi))
} else {
valgrindChangeStack(gp.valgrindStackID, unsafe.Pointer(new.lo), unsafe.Pointer(new.hi))
}
}
// free old stack
if stackPoisonCopy != 0 {
fillstack(old, 0xfc)