[release-branch.go1.26] all: merge master (f6ebd91) into release-branch.go1.26

Merge List:

+ 2026-01-07 f6ebd91129 all: update vendored x/tools
+ 2026-01-06 d1d0fc7a97 os/exec: avoid atomic.Bool for Cmd.startCalled
+ 2026-01-05 9b2e3b9a02 simd/archsimd: use V(P)MOVMSK for mask ToBits if possible
+ 2026-01-02 f8ee0f8475 cmd/go/testdata/vcstest/git: use git commands that work on older git versions
+ 2026-01-02 b094749bad test/codegen: codify bit related code generation for arm64
+ 2026-01-02 e84983fa40 cmd/compile: optimize SIMD IsNaN.Or(IsNaN)
+ 2026-01-02 8244b85677 simd/archsimd: add tests for IsNaN
+ 2026-01-02 13440fb518 simd/archsimd: make IsNaN unary
+ 2026-01-02 c3550b3352 simd/archsimd: correct documentation of Mask types
+ 2026-01-02 34ad26341d net/rpc: correct comment for isExportedOrBuiltinType function
+ 2025-12-30 b28808d838 cmd/go/internal/modindex: fix obvious bug using failed type assertion
+ 2025-12-30 d64add4d60 simd/archsimd: adjust documentations slightly
+ 2025-12-30 1843cfbcd6 runtime/secret: make tests more sturdy
+ 2025-12-30 fd45d70799 all: fix some minor grammatical issues in the comments
+ 2025-12-30 df4e08ac65 test/codegen: fix a tab in comparisons.go to ensure pattern works
+ 2025-12-30 cd668d744f cmd/compile: disable inlining for functions using runtime.deferrangefunc
+ 2025-12-29 06eff0f7c3 simd/archsimd: add tests for Saturate-Concat operations
+ 2025-12-29 110aaf7137 simd/archsimd: add tests for Saturate operations
+ 2025-12-29 22e7b94e7f simd/archsimd: add tests for ExtendLo operations
+ 2025-12-29 76dddce293 simd/archsimd: remove redundant suffix of ExtendLo operations
+ 2025-12-29 6ecdd2fc6e simd/archsimd: add more tests for Convert operations
+ 2025-12-29 e0c99fe285 simd/archsimd: add more tests for Truncate operations
+ 2025-12-29 08369369e5 reflect: document Call/CallSlice panic when v is unexported field
+ 2025-12-29 ca8effbde1 internal/coverage/decodemeta: correct wording in unknown version error
+ 2025-12-29 0b06b68e21 encoding/gob: clarify docs about pointers to zero values not being sent
+ 2025-12-29 9cb3edbfe9 regexp: standardize error message format in find_test.go
+ 2025-12-29 b3ed0627ce tests: improve consistency and clarity of test diagnostics
+ 2025-12-29 3dcb48d298 test: follow got/want convention in uintptrescapes test
+ 2025-12-29 f7b7e94b0a test: clarify log message for surrogate UTF-8 check
+ 2025-12-29 e790d59674 simd/archsimd: add tests for Truncate operations
+ 2025-12-27 f4cec7917c cmd: fix unused errors reported by ineffassign
+ 2025-12-27 ca13fe02c4 simd/archsimd: add more tests for Convert operations
+ 2025-12-27 037c047f2c simd/archsimd: add more tests for Extend operations
+ 2025-12-26 7971fcdf53 test/codegen: tidy tests for bits
+ 2025-12-24 0f620776d7 simd/archsimd: fix "go generate" command
+ 2025-12-24 a5fe8c07ae simd/archsimd: guard test helpers with amd64 tag
+ 2025-12-23 a23d1a4ebe bytes: improve consistency in split test messages
+ 2025-12-23 866e461b96 cmd/go: update pkgsite doc command to v0.0.0-20251223195805-1a3bd3c788fe
+ 2025-12-23 08dc8393d7 time: skip test that will fail with GO111MODULE=off
+ 2025-12-23 43ebed88cc runtime: improve a log message in TestCleanupLost
+ 2025-12-23 81283ad339 runtime: fix nGsyscallNoP accounting
+ 2025-12-23 3e0e1667f6 test/codegen: codify bit related code generation for riscv64
+ 2025-12-23 3faf988f21 errors: add a test verifying join does not flatten errors
+ 2025-12-23 2485a0bc2c cmd/asm/internal/asm: run riscv64 end-to-end tests for each profile
+ 2025-12-23 8254d66eab cmd/asm/internal/asm: abort end to end test if assembly failed
+ 2025-12-23 1b3db48db7 Revert "errors: optimize errors.Join for single unwrappable errors"
+ 2025-12-23 b6b8b2fe6e cmd/compile: handle propagating an out-of-range jump table index
+ 2025-12-22 2cd0371a0a debug/pe: avoid panic in File.ImportedSymbols
+ 2025-12-22 91435be153 runtime: revert entry point on freebsd/arm64
+ 2025-12-22 c1efada1d2 simd/archsimd: correct documentation for pairwise operations
+ 2025-12-22 3d77a0b15e os/exec: second call to Cmd.Start is always an error
+ 2025-12-20 7ecb1f36ac simd/archsimd: add HasAVX2() guards to tests that need them
+ 2025-12-19 70c22e0ad7 simd/archsimd: delete DotProductQuadruple methods for now
+ 2025-12-19 42cda7c1df simd/archsimd: add Grouped for 256- and 512-bit SaturateTo(U)Int16Concat, and fix type
+ 2025-12-19 baa0ae3aaa simd/archsimd: correct type and instruction for SaturateToUint8
+ 2025-12-19 d46c58debb go/doc: link to struct fields in the same package
+ 2025-12-19 25ed6c7f9b cmd/go/internal/doc: update pkgsite version
+ 2025-12-19 4411edf972 simd/archsimd: reword documentation for some operations
+ 2025-12-19 7d9418a19c simd/archsimd: reword documentation of comparison operations
+ 2025-12-18 d00e96d3ae internal/cpu: repair VNNI feature check
+ 2025-12-18 cfc024daeb simd/archsimd: reword documentation for conversion ops
+ 2025-12-17 ad91f5d241 simd/archsimd: reword documentation of shfit operations
+ 2025-12-17 b8c4cc63e7 runtime: keep track of secret allocation size
+ 2025-12-17 8564fede89 cmd/go: remove reference to no longer existing -i flag
+ 2025-12-17 eecdb61eeb crypto: rename fips140v2.0 to fips140v1.26
+ 2025-12-17 05e41225f6 simd/archsimd: reword documentation of As methods
+ 2025-12-17 516699848b runtime/secret: warn users about allocations, loosen guarantees
+ 2025-12-16 8c28ab936a cmd/cgo: don't emit C local if it is not used
+ 2025-12-16 65b71c11d4 crypto/internal/fips140only: test fips140=only mode
+ 2025-12-16 ea1aa76554 go/doc: exclude examples with results
+ 2025-12-16 5046bdf8a6 crypto/tls: reject trailing messages after client/server hello
+ 2025-12-16 3f6eabdf09 cmd/compile: use unsigned constant when folding loads for SIMD ops with constants
+ 2025-12-16 a4b5b92055 cmd/dist: preserve existing GOEXPERIMENTs when running tests with additional experiments

Change-Id: I84ad4ceba344761142b98587c07d186cf2d638ff

1 files changed, 9 insertions, 1 deletions

diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
index e84ebfc453..aa7a6be7f0 100644
--- a/src/os/exec/exec.go
+++ b/src/os/exec/exec.go
@@ -102,6 +102,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync/atomic"
 	"syscall"
 	"time"
 )
@@ -354,6 +355,11 @@ type Cmd struct {
 	// the work of resolving the extension, so Start doesn't need to do it again.
 	// This is only used on Windows.
 	cachedLookExtensions struct{ in, out string }
+
+	// startCalled records that Start was attempted, regardless of outcome.
+	// (Until go.dev/issue/77075 is resolved, we use atomic.SwapInt32,
+	// not atomic.Bool.Swap, to avoid triggering the copylocks vet check.)
+	startCalled int32
 }
 
 // A ctxResult reports the result of watching the Context associated with a
@@ -635,7 +641,8 @@ func (c *Cmd) Run() error {
 func (c *Cmd) Start() error {
 	// Check for doubled Start calls before we defer failure cleanup. If the prior
 	// call to Start succeeded, we don't want to spuriously close its pipes.
-	if c.Process != nil {
+	// It is an error to call Start twice even if the first call did not create a process.
+	if atomic.SwapInt32(&c.startCalled, 1) != 0 {
 		return errors.New("exec: already started")
 	}
 
@@ -647,6 +654,7 @@ func (c *Cmd) Start() error {
 		if !started {
 			closeDescriptors(c.parentIOPipes)
 			c.parentIOPipes = nil
+			c.goroutine = nil // aid GC, finalization of pipe fds
 		}
 	}()