Introduction: The Forgotten Architecture In the landscape of operating system development, two primary execution environments dominate: 32-bit (x86) and 64-bit (x86-64, often called x64) . The former is the aging workhorse of the late 90s and early 2000s; the latter is the current standard. Yet, lurking in the shadow of these two giants is a third, often misunderstood beast: x32 .
For the systems programmer, studying x32 offers a profound lesson: Every pointer dereference carries the weight of its width. And sometimes, the most optimal path is the one the hardware never expected you to take. x32 driver
To truly understand the x32 driver, one must stop looking for a file named x32.sys and start looking at the entry_64.S file in the Linux kernel source—because in there, guarded by a single bitmask test on orig_ax , lies a ghost of what computing could have been: fast, lean, and forever limited to 4GB. Introduction: The Forgotten Architecture In the landscape of
static bool is_x32_task(struct task_struct *task) { return task->thread_info.status & TS_COMPAT; } Wait—that is too generic. Actually, the kernel uses: For the systems programmer, studying x32 offers a
#define in_x32_syscall() (task_pt_regs(current)->orig_ax & __X32_SYSCALL_BIT) In arch/x86/entry/entry_64.S , the system call entry point checks the system call number. If the __X32_SYSCALL_BIT (bit 30) is set in orig_ax , it jumps to the x32 syscall table. Otherwise, it routes to the 64-bit table. For a 32-bit (non-x32) process, a completely different entry path ( ia32 ) is used, which involves switching to 32-bit compatibility mode.