From the very little research I did signal handlers actually use the same stack as the user-space thread it runs on, unless sigaltstack is used to set up a sepa

From the very little research I did signal handlers actually use the same stack as the user-space thread it runs on, unless sigaltstack is used to set up a separate stack. Although it's probably possible for the kernel to adjust the stack pointer over the red-zone before returning to user-space, so the signal handler can run safely.