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:
#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.
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.
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.
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:
#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. x32 driver
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. Otherwise, it routes to the 64-bit table
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. And sometimes, the most optimal path is the
