[PATCH] consolidate do_bug_frame() / bug_fn_t

[Jan Beulich <jbeulich@xxxxxxxx>]

The type not being used in do_bug_frame() is suspicious. Apparently
that's solely because the type uses a pointer-to-const parameter,
when run_in_exception_handler() wants functions taking pointer-to-non-
const. Drop the const, in turn requiring Arm's do_bug_frame() to also
have its const dropped. This then brings that function also closer to
the common one, with Arm's use of vaddr_t remaining as a difference.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
This is an alternative proposal to
https://lists.xen.org/archives/html/xen-devel/2023-12/msg01385.html,
albeit without paving a road towards Andrew's desire of getting rid of
show_execution_state_nonconst() again. Retaining (and propagating) the
const would imply the need to cast away the const-ness somewhere on (at
least) the path to invoking gdb stub code. Personally I'm averse to such
casting away of const-ness ...

--- a/xen/arch/arm/include/asm/traps.h
+++ b/xen/arch/arm/include/asm/traps.h
@@ -69,7 +69,7 @@ void do_cp(struct cpu_user_regs *regs, c
 void do_trap_smc(struct cpu_user_regs *regs, const union hsr hsr);
 void do_trap_hvc_smccc(struct cpu_user_regs *regs);
 
-int do_bug_frame(const struct cpu_user_regs *regs, vaddr_t pc);
+int do_bug_frame(struct cpu_user_regs *regs, vaddr_t pc);
 
 void noreturn do_unexpected_trap(const char *msg,
                                  const struct cpu_user_regs *regs);
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1202,7 +1202,7 @@ void do_unexpected_trap(const char *msg,
     panic("CPU%d: Unexpected Trap: %s\n", smp_processor_id(), msg);
 }
 
-int do_bug_frame(const struct cpu_user_regs *regs, vaddr_t pc)
+int do_bug_frame(struct cpu_user_regs *regs, vaddr_t pc)
 {
     const struct bug_frame *bug = NULL;
     const char *prefix = "", *filename, *predicate;
--- a/xen/common/bug.c
+++ b/xen/common/bug.c
@@ -63,14 +63,10 @@ int do_bug_frame(struct cpu_user_regs *r
 
     if ( id == BUGFRAME_run_fn )
     {
-        void (*fn)(struct cpu_user_regs *) = bug_ptr(bug);
+        bug_fn_t *fn = bug_ptr(bug);
 
         fn(regs);
 
-        /* Re-enforce consistent types, because of the casts involved. */
-        if ( false )
-            run_in_exception_handler(fn);
-
         return id;
     }
 
--- a/xen/include/xen/bug.h
+++ b/xen/include/xen/bug.h
@@ -101,12 +101,11 @@ struct bug_frame {
 #endif
 
 struct cpu_user_regs;
-typedef void bug_fn_t(const struct cpu_user_regs *regs);
+typedef void bug_fn_t(struct cpu_user_regs *regs);
 
 #ifndef run_in_exception_handler
 
-static void always_inline run_in_exception_handler(
-    void (*fn)(struct cpu_user_regs *regs))
+static void always_inline run_in_exception_handler(bug_fn_t *fn)
 {
     BUG_FRAME(BUGFRAME_run_fn, 0, fn, 0, NULL);
 }