runtime: SEGV in gcBgMarkStartWorkers

[gopherbot]

#!watchflakes
default <- pkg == "golang.org/x/tools/go/ssa" && test == "TestGenericAliases"

Issue created automatically to collect these failures.

Example (log):

=== RUN   TestGenericAliases
    builder_test.go:1122: out=<<--- FAIL: TestGenericAliases (0.35s)
            testutil_test.go:117: go tool not available: /Volumes/Work/s/w/ir/x/w/goroot/bin/go build -o /dev/null /Volumes/Work/s/w/ir/x/t/testenv-3396701366/main.go: exit status 1
                # command-line-arguments
                unexpected fault address 0x5ad00000415
                fatal error: fault
                [signal SIGSEGV: segmentation violation code=0x1 addr=0x5ad00000415 pc=0xf827c69]
                
                goroutine 1 gp=0xc000004380 m=5 mp=0xc0004a8008 [running]:
                runtime.throw({0xf9268ed?, 0xfa32740?})
...
                runtime.gcBgMarkStartWorkers.gowrap1()
                	runtime/mgc.go:1373 +0x25 fp=0xc0001787e0 sp=0xc0001787c8 pc=0xf683c65
                runtime.goexit({})
                	runtime/asm_amd64.s:1693 +0x1 fp=0xc0001787e8 sp=0xc0001787e0 pc=0xf6def41
                created by runtime.gcBgMarkStartWorkers in goroutine 1
                	runtime/mgc.go:1373 +0x105
        FAIL
        >>
    builder_test.go:1130: exited 1, want 0
--- FAIL: TestGenericAliases (0.39s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "golang.org/x/tools/go/ssa" && test == "TestGenericAliases"

2025-07-09 19:52 x_tools-gotip-darwin-amd64_12 tools@63f81c9f go@67c17044 x/tools/go/ssa.TestGenericAliases (log)

=== RUN   TestGenericAliases
    builder_test.go:1122: out=<<--- FAIL: TestGenericAliases (0.35s)
            testutil_test.go:117: go tool not available: /Volumes/Work/s/w/ir/x/w/goroot/bin/go build -o /dev/null /Volumes/Work/s/w/ir/x/t/testenv-3396701366/main.go: exit status 1
                # command-line-arguments
                unexpected fault address 0x5ad00000415
                fatal error: fault
                [signal SIGSEGV: segmentation violation code=0x1 addr=0x5ad00000415 pc=0xf827c69]
                
                goroutine 1 gp=0xc000004380 m=5 mp=0xc0004a8008 [running]:
                runtime.throw({0xf9268ed?, 0xfa32740?})
...
                runtime.gcBgMarkStartWorkers.gowrap1()
                	runtime/mgc.go:1373 +0x25 fp=0xc0001787e0 sp=0xc0001787c8 pc=0xf683c65
                runtime.goexit({})
                	runtime/asm_amd64.s:1693 +0x1 fp=0xc0001787e8 sp=0xc0001787e0 pc=0xf6def41
                created by runtime.gcBgMarkStartWorkers in goroutine 1
                	runtime/mgc.go:1373 +0x105
        FAIL
        >>
    builder_test.go:1130: exited 1, want 0
--- FAIL: TestGenericAliases (0.39s)

— watchflakes