zig_probe_stack

pub fn zig_probe_stack() callconv(.naked) void

File

Code

pub fn zig_probe_stack() callconv(.naked) void {
    @setRuntimeSafety(false);

    // Versions of the Linux kernel before 5.1 treat any access below SP as
    // invalid so let's update it on the go, otherwise we'll get a segfault
    // instead of triggering the stack growth.

    switch (arch) {
        .x86_64 => {
            // %rax = probe length, %rsp = stack pointer
            asm volatile (
                \\        push   %%rcx
                \\        mov    %%rax, %%rcx
                \\        cmp    $0x1000,%%rcx
                \\        jb     2f
                \\ 1:
                \\        sub    $0x1000,%%rsp
                \\        orl    $0,16(%%rsp)
                \\        sub    $0x1000,%%rcx
                \\        cmp    $0x1000,%%rcx
                \\        ja     1b
                \\ 2:
                \\        sub    %%rcx, %%rsp
                \\        orl    $0,16(%%rsp)
                \\        add    %%rax,%%rsp
                \\        pop    %%rcx
                \\        ret
            );
        },
        .x86 => {
            // %eax = probe length, %esp = stack pointer
            asm volatile (
                \\        push   %%ecx
                \\        mov    %%eax, %%ecx
                \\        cmp    $0x1000,%%ecx
                \\        jb     2f
                \\ 1:
                \\        sub    $0x1000,%%esp
                \\        orl    $0,8(%%esp)
                \\        sub    $0x1000,%%ecx
                \\        cmp    $0x1000,%%ecx
                \\        ja     1b
                \\ 2:
                \\        sub    %%ecx, %%esp
                \\        orl    $0,8(%%esp)
                \\        add    %%eax,%%esp
                \\        pop    %%ecx
                \\        ret
            );
        },
        else => {},
    }

    unreachable;
}