arm64: debug: remove debug exception registration infrastructure

JIRA: https://issues.redhat.com/browse/RHEL-65658

CONFLICTS: context due to the lack of commit 8ce71d2 ("arm64/traps:
           Handle GCS exceptions") and commit 25b8400 ("arm64: Support
           Clang UBSAN trap codes for better reporting")

commit a8b8cce
Author: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Date:   Mon Jul 7 12:41:09 2025 +0100

    arm64: debug: remove debug exception registration infrastructure

    Now that debug exceptions are handled individually and without the need
    for dynamic registration, remove the unused registration infrastructure.

    This removes the external caller for `debug_exception_enter()` and
    `debug_exception_exit()`.
    Make them static again and remove them from the header.

    Remove `early_brk64()` as it has been made redundant by
    (arm64: debug: split brk64 exception entry) and is not used anymore.
    Note : in `early_brk64()` `bug_brk_handler()` is called unconditionally
    as a fall-through, but now `call_break_hook()` only calls it if the
    immediate matches.
    This does not change the behaviour in early boot, as if
    `bug_brk_handler()` was called on a non-BUG immediate it would return
    DBG_HOOK_ERROR anyway, which `call_break_hook()` will do if no immediate
    matches.

    Remove `trap_init()`, as it would be empty and a weak definition already
    exists in `init/main.c`.

    Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
    Tested-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
    Reviewed-by: Will Deacon <will@kernel.org>
    Acked-by: Mark Rutland <mark.rutland@arm.com>
    Link: https://lore.kernel.org/r/20250707114109.35672-14-ada.coupriediaz@arm.com
    Signed-off-by: Will Deacon <will@kernel.org>

Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>

Author: lclaudio

arch/arm64/include/asm/debug-monitors.h

@@ -93,7 +93,5 @@ static inline bool try_step_suspended_breakpoints(struct pt_regs *regs)
 
 bool try_handle_aarch32_break(struct pt_regs *regs);
 
-void debug_traps_init(void);
-
 #endif	/* __ASSEMBLY */
 #endif	/* __ASM_DEBUG_MONITORS_H */

arch/arm64/include/asm/exception.h

@@ -57,8 +57,6 @@ void do_el0_undef(struct pt_regs *regs, unsigned long esr);
 void do_el1_undef(struct pt_regs *regs, unsigned long esr);
 void do_el0_bti(struct pt_regs *regs);
 void do_el1_bti(struct pt_regs *regs, unsigned long esr);
-void do_debug_exception(unsigned long addr_if_watchpoint, unsigned long esr,
-			struct pt_regs *regs);
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 void do_breakpoint(unsigned long esr, struct pt_regs *regs);
 void do_watchpoint(unsigned long addr, unsigned long esr,
@@ -91,8 +89,4 @@ void do_serror(struct pt_regs *regs, unsigned long esr);
 void do_signal(struct pt_regs *regs);
 
 void __noreturn panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far);
-
-void debug_exception_enter(struct pt_regs *regs);
-void debug_exception_exit(struct pt_regs *regs);
-
 #endif	/* __ASM_EXCEPTION_H */

arch/arm64/include/asm/system_misc.h

@@ -25,10 +25,6 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
 		      int signo, int sicode, unsigned long far,
 		      unsigned long err);
 
-void hook_debug_fault_code(int nr, int (*fn)(unsigned long, unsigned long,
-					     struct pt_regs *),
-			   int sig, int code, const char *name);
-
 struct mm_struct;
 extern void __show_regs(struct pt_regs *);
 

arch/arm64/kernel/debug-monitors.c

@@ -313,9 +313,6 @@ bool try_handle_aarch32_break(struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(try_handle_aarch32_break);
 
-void __init debug_traps_init(void)
-{}
-
 /* Re-enable single step for syscall restarting. */
 void user_rewind_single_step(struct task_struct *task)
 {

arch/arm64/kernel/entry-common.c

@@ -425,7 +425,7 @@ static inline void fp_user_discard(void)
  * accidentally schedule in exception context and it will force a warning
  * if we somehow manage to schedule by accident.
  */
-void debug_exception_enter(struct pt_regs *regs)
+static void debug_exception_enter(struct pt_regs *regs)
 {
 	preempt_disable();
 
@@ -434,7 +434,7 @@ void debug_exception_enter(struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(debug_exception_enter);
 
-void debug_exception_exit(struct pt_regs *regs)
+static void debug_exception_exit(struct pt_regs *regs)
 {
 	preempt_enable_no_resched();
 }

arch/arm64/kernel/traps.c

@@ -1061,27 +1061,3 @@ int kasan_brk_handler(struct pt_regs *regs, unsigned long esr)
 	return DBG_HOOK_HANDLED;
 }
 #endif
-
-
-/*
- * Initial handler for AArch64 BRK exceptions
- * This handler only used until debug_traps_init().
- */
-int __init early_brk64(unsigned long addr, unsigned long esr,
-		struct pt_regs *regs)
-{
-#ifdef CONFIG_CFI_CLANG
-	if (esr_is_cfi_brk(esr))
-		return cfi_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
-#endif
-#ifdef CONFIG_KASAN_SW_TAGS
-	if ((esr_brk_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
-		return kasan_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
-#endif
-	return bug_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
-}
-
-void __init trap_init(void)
-{
-	debug_traps_init();
-}

arch/arm64/mm/fault.c

@@ -52,18 +52,12 @@ struct fault_info {
 };
 
 static const struct fault_info fault_info[];
-static struct fault_info debug_fault_info[];
 
 static inline const struct fault_info *esr_to_fault_info(unsigned long esr)
 {
 	return fault_info + (esr & ESR_ELx_FSC);
 }
 
-static inline const struct fault_info *esr_to_debug_fault_info(unsigned long esr)
-{
-	return debug_fault_info + DBG_ESR_EVT(esr);
-}
-
 static void data_abort_decode(unsigned long esr)
 {
 	unsigned long iss2 = ESR_ELx_ISS2(esr);
@@ -857,53 +851,6 @@ void do_sp_pc_abort(unsigned long addr, unsigned long esr, struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(do_sp_pc_abort);
 
-/*
- * __refdata because early_brk64 is __init, but the reference to it is
- * clobbered at arch_initcall time.
- * See traps.c and debug-monitors.c:debug_traps_init().
- */
-static struct fault_info __refdata debug_fault_info[] = {
-	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware breakpoint"	},
-	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware single-step"	},
-	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware watchpoint"	},
-	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 3"		},
-	{ do_bad,	SIGTRAP,	TRAP_BRKPT,	"aarch32 BKPT"		},
-	{ do_bad,	SIGKILL,	SI_KERNEL,	"aarch32 vector catch"	},
-	{ early_brk64,	SIGTRAP,	TRAP_BRKPT,	"aarch64 BRK"		},
-	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 7"		},
-};
-
-void __init hook_debug_fault_code(int nr,
-				  int (*fn)(unsigned long, unsigned long, struct pt_regs *),
-				  int sig, int code, const char *name)
-{
-	BUG_ON(nr < 0 || nr >= ARRAY_SIZE(debug_fault_info));
-
-	debug_fault_info[nr].fn		= fn;
-	debug_fault_info[nr].sig	= sig;
-	debug_fault_info[nr].code	= code;
-	debug_fault_info[nr].name	= name;
-}
-
-void do_debug_exception(unsigned long addr_if_watchpoint, unsigned long esr,
-			struct pt_regs *regs)
-{
-	const struct fault_info *inf = esr_to_debug_fault_info(esr);
-	unsigned long pc = instruction_pointer(regs);
-
-	debug_exception_enter(regs);
-
-	if (user_mode(regs) && !is_ttbr0_addr(pc))
-		arm64_apply_bp_hardening();
-
-	if (inf->fn(addr_if_watchpoint, esr, regs)) {
-		arm64_notify_die(inf->name, regs, inf->sig, inf->code, pc, esr);
-	}
-
-	debug_exception_exit(regs);
-}
-NOKPROBE_SYMBOL(do_debug_exception);
-
 /*
  * Used during anonymous page fault handling.
  */