Alright, let's break down this problem. The user is reporting an issue where QEMU isn't handling the `set_robust_list` system call properly. They've provided a test program that works on native Linux but fails when run in QEMU. First, I'll look at what `set_robust_list` does. It's used by glibc for robust mutexes, which are important for thread safety across process boundaries. If this syscall isn't implemented correctly in QEMU, applications relying on it will fail. The test program shows that on native Linux, both calls to `set_robust_list` work as expected. But when run in QEMU, the second call fails with "Function not implemented," indicating that QEMU doesn't support this system call at all. This means any application depending on robust mutexes won't function correctly under QEMU. Looking deeper, glibc uses `set_robust_list` during initialization to check for robust list support. If it's missing, functions like `pthread_mutex_init` with robust attributes will return `ENOTSUP`, preventing the use of these mutex types. This is critical because robust mutexes are vital for reliable process synchronization. Since QEMU emulates a system, it should accurately implement all necessary system calls to ensure compatibility. The absence of `set_robust_list` breaks this compatibility, especially for applications that rely on pthread robust features. So, the issue here is a missing or improperly implemented system call in QEMU's Linux user mode emulation. This directly affects runtime behavior because applications can't use certain pthread functionalities when running under QEMU. The bug report describes an issue where the `set_robust_list` system call is not properly handled by QEMU, leading to errors when applications try to use it. Since this relates to a specific system call implementation in QEMU, the category is: **syscall** The error occurs because the `set_robust_list` syscall isn't implemented in QEMU's user mode emulation for Linux targets. This affects applications that rely on robust mutexes provided by glibc, such as those using named locks or process-shared mutexes. To fix this, QEMU needs to implement the `set_robust_list` system call correctly in its Linux user mode codebase to ensure compatibility with applications expecting this functionality.