amd64: Use a larger boot stack

[markj]

Summary

With sanitizers enabled, it becomes possible to overflow the stack when
only a single page is used. Follow arm64's example and use the default
kernel stack size instead. This is a bit wasteful, but without a guard
page, overflow is difficult to debug.

[kib]

Could you only enable it for sanitizers enable case?

[markj]

In D41166#937374, @kib wrote:

Could you only enable it for sanitizers enable case?

I could, but is it really important to save three pages? We already consume more than half a page for the stack below, not sure if it's the worst case. Stack overflow corrupts adjacent pages in the BSS, which can take a lot of effort to debug. I'm sure that someday we'll hit the limit in GENERIC kernels.

#0  vsscanf (inp=<optimized out>, ap=0xffffffff81791820, fmt0=<optimized out>) at /root/freebsd/sys/kern/subr_scanf.c:132                                                                                                                                                                                                     
#1  sscanf (ibuf=ibuf@entry=0xffffffff81fc81a6 "acpi_throttle.0.disabled=1", fmt=<optimized out>) at /root/freebsd/sys/kern/subr_scanf.c:102                                                                                                                                                                                  
#2  0xffffffff80b9a6e2 in res_find (hintp_cookie=hintp_cookie@entry=0xffffffff817919e0, line=line@entry=0xffffffff817919ec, startln=startln@entry=0x0, 
    name=name@entry=0xffffffff812179e3 "acpi", unit=unit@entry=0xffffffff817919dc, resname=resname@entry=0xffffffff81223da5 "disabled", value=0x0, 
    ret_name=0x0, ret_namelen=0x0, ret_unit=0x0, ret_resname=0x0, ret_resnamelen=0x0, ret_value=0xffffffff817919d0)
    at /root/freebsd/sys/kern/subr_hints.c:241
#3  0xffffffff80b99d05 in resource_find (line=0xffffffff817919ec, startln=0x0, name=0xffffffff812179e3 "acpi", unit=0xffffffff817919dc, 
    resname=0xffffffff81223da5 "disabled", value=0x0, ret_name=0x0, ret_namelen=0x0, ret_unit=0x0, ret_resname=0x0, ret_resnamelen=0x0, 
    ret_value=0xffffffff817919d0) at /root/freebsd/sys/kern/subr_hints.c:323
#4  resource_int_value (name=0xffffffff812179e3 "acpi", unit=unit@entry=0, resname=0xffffffff81223da5 "disabled", result=result@entry=0xffffffff81791a2c)
    at /root/freebsd/sys/kern/subr_hints.c:350
#5  0xffffffff80b9a0e8 in resource_disabled (name=0xffffffff81fc81c0 "", unit=-2128589492, unit@entry=0) at /root/freebsd/sys/kern/subr_hints.c:489
#6  0xffffffff81013b15 in acpi_find_table (sig=0xffffffff81184309 "FACP") at /root/freebsd/sys/amd64/acpica/acpi_machdep.c:175
#7  0xffffffff81005485 in acpi_get_fadt_bootflags (flagsp=flagsp@entry=0xffffffff81791abe) at /root/freebsd/sys/x86/x86/cpu_machdep.c:1514
#8  0xffffffff8098cb96 in vga_acpi_disabled () at /root/freebsd/sys/dev/vt/hw/vga/vt_vga.c:1270                                                                
#9  vga_probe (vd=<optimized out>) at /root/freebsd/sys/dev/vt/hw/vga/vt_vga.c:1282                                                                            
#10 0xffffffff8099290e in vtterm_cnprobe (tm=0xffffffff816ab320 <vt_consterm>, cp=0xffffffff816ab120 <vt_consterm_consdev>)
    at /root/freebsd/sys/dev/vt/vt_core.c:1656
#11 0xffffffff80add88e in cninit () at /root/freebsd/sys/kern/kern_cons.c:168
#12 0xffffffff81022f81 in hammer_time (modulep=<optimized out>, physfree=<optimized out>) at /root/freebsd/sys/amd64/amd64/machdep.c:1552
#13 0xffffffff8037e01b in btext () at /root/freebsd/sys/amd64/amd64/locore.S:88