x86: Remove gdbstub

In 13y of working on Xen, I've never seen seen it used.  The implementation
was introduced (commit b69f92f, Jul 28 2004) with known issues such as:

  /* Resuming after we've stopped used to work, but more through luck
     than any actual intention.  It doesn't at the moment. */

which appear to have gone unfixed for the 20 years since.

Nowadays there are more robust ways of inspecting crashed state, such as a
kexec crash kernel, or running Xen in a VM.

This will allow us to clean up some hooks around the codebase which are
proving awkward for other tasks.

Signed-off-by: Andrew Cooper <[email protected]>
Acked-by: Jan Beulich <[email protected]>

Author: andyhhp

CHANGELOG.md

@@ -25,6 +25,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - /usr/bin/pygrub symlink.  This was deprecated in Xen 4.2 (2012) but left for
   compatibility reasons.  VMs configured with bootloader="/usr/bin/pygrub"
   should be updated to just bootloader="pygrub".
+- The Xen gdbstub on x86.
 
 ## [4.18.0](https://xenbits.xenproject.org/gitweb/?p=xen.git;a=shortlog;h=RELEASE-4.18.0) - 2023-11-16
 

docs/misc/xen-command-line.pandoc

@@ -1242,13 +1242,6 @@ requirement can be relaxed.  This option is particularly useful for nested
 virtualization, to allow the L1 hypervisor to use EPT even if the L0 hypervisor
 does not provide `VM_ENTRY_LOAD_GUEST_PAT`.
 
-### gdb
-> `= com1[H,L] | com2[H,L] | dbgp`
-
-> Default: ``
-
-Specify which console gdbstub should use. See **console**.
-
 ### gnttab
 > `= List of [ max-ver:<integer>, transitive=<bool>, transfer=<bool> ]`
 

xen/Kconfig.debug

@@ -13,13 +13,6 @@ config DEBUG
 
 if DEBUG || EXPERT
 
-config CRASH_DEBUG
-	bool "Crash Debugging Support"
-	depends on X86
-	---help---
-	  If you want to attach gdb to Xen to debug Xen if it crashes
-	  then say Y.
-
 config GDBSX
 	bool "Guest debugging with gdbsx"
 	depends on X86

xen/arch/x86/Makefile

@@ -35,7 +35,6 @@ obj-y += e820.o
 obj-y += emul-i8254.o
 obj-y += extable.o
 obj-y += flushtlb.o
-obj-$(CONFIG_CRASH_DEBUG) += gdbstub.o
 obj-$(CONFIG_GDBSX) += gdbsx.o
 obj-y += hypercall.o
 obj-y += i387.o

xen/arch/x86/gdbstub.c

@@ -12,5 +12,3 @@ obj-$(CONFIG_COMPAT) += domain.o
 obj-$(CONFIG_COMPAT) += cpu_idle.o
 obj-$(CONFIG_COMPAT) += cpufreq.o
 obj-bin-$(CONFIG_KEXEC) += kexec_reloc.o
-
-obj-$(CONFIG_CRASH_DEBUG)   += gdbstub.o

xen/arch/x86/x86_64/Makefile

@@ -12,7 +12,6 @@ obj-$(CONFIG_OVERLAY_DTB) += dt-overlay.o
 obj-y += event_2l.o
 obj-y += event_channel.o
 obj-y += event_fifo.o
-obj-$(CONFIG_CRASH_DEBUG) += gdbstub.o
 obj-$(CONFIG_GRANT_TABLE) += grant_table.o
 obj-y += guestcopy.o
 obj-bin-y += gunzip.init.o