xen/virtual-region: Rework how bugframe linkage works

The start/stop1/etc linkage scheme predates struct virtual_region, and as
setup_virtual_regions() shows, it's awkward to express in the new scheme.

Change the linker to provide explicit start/stop symbols for each bugframe
type, and change virtual_region to have a stop pointer rather than a count.

This marginally simplifies both do_bug_frame()s and prepare_payload(), but it
massively simplifies setup_virtual_regions() by allowing the compiler to
initialise the .frame[] array at build time.

virtual_region.c is the only user of the linker symbols, and this is unlikely
to change given the purpose of struct virtual_region, so move their externs
out of bug.h

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>

xen/arch/arm/traps.c

@@ -1226,10 +1226,9 @@ int do_bug_frame(const struct cpu_user_regs *regs, vaddr_t pc)
         for ( id = 0; id < BUGFRAME_NR; id++ )
         {
             const struct bug_frame *b;
-            unsigned int i;
 
-            for ( i = 0, b = region->frame[id].bugs;
-                  i < region->frame[id].n_bugs; b++, i++ )
+            for ( b = region->frame[id].start;
+                  b < region->frame[id].stop; b++ )
             {
                 if ( ((vaddr_t)bug_loc(b)) == pc )
                 {

xen/common/bug.c

@@ -25,10 +25,9 @@ int do_bug_frame(const struct cpu_user_regs *regs, unsigned long pc)
     for ( id = 0; id < BUGFRAME_NR; id++ )
     {
         const struct bug_frame *b;
-        size_t i;
 
-        for ( i = 0, b = region->frame[id].bugs;
-              i < region->frame[id].n_bugs; b++, i++ )
+        for ( b = region->frame[id].start;
+              b < region->frame[id].stop; b++ )
         {
             if ( bug_loc(b) == pc )
             {

xen/common/livepatch.c

@@ -804,12 +804,11 @@ static int prepare_payload(struct payload *payload,
         if ( !sec )
             continue;
 
-        if ( !section_ok(elf, sec, sizeof(*region->frame[i].bugs)) )
+        if ( !section_ok(elf, sec, sizeof(*region->frame[i].start)) )
             return -EINVAL;
 
-        region->frame[i].bugs = sec->load_addr;
-        region->frame[i].n_bugs = sec->sec->sh_size /
-                                  sizeof(*region->frame[i].bugs);
+        region->frame[i].start = sec->load_addr;
+        region->frame[i].stop  = sec->load_addr + sec->sec->sh_size;
     }
 
     sec = livepatch_elf_sec_by_name(elf, ".altinstructions");

xen/common/virtual_region.c

@@ -9,12 +9,25 @@
 #include <xen/spinlock.h>
 #include <xen/virtual_region.h>
 
+extern const struct bug_frame
+    __start_bug_frames_0[], __stop_bug_frames_0[],
+    __start_bug_frames_1[], __stop_bug_frames_1[],
+    __start_bug_frames_2[], __stop_bug_frames_2[],
+    __start_bug_frames_3[], __stop_bug_frames_3[];
+
 static struct virtual_region core = {
     .list = LIST_HEAD_INIT(core.list),
     .text_start = _stext,
     .text_end = _etext,
     .rodata_start = _srodata,
     .rodata_end = _erodata,
+
+    .frame = {
+        { __start_bug_frames_0, __stop_bug_frames_0 },
+        { __start_bug_frames_1, __stop_bug_frames_1 },
+        { __start_bug_frames_2, __stop_bug_frames_2 },
+        { __start_bug_frames_3, __stop_bug_frames_3 },
+    },
 };
 
 /* Becomes irrelevant when __init sections are cleared. */
@@ -22,6 +35,13 @@ static struct virtual_region core_init __initdata = {
     .list = LIST_HEAD_INIT(core_init.list),
     .text_start = _sinittext,
     .text_end = _einittext,
+
+    .frame = {
+        { __start_bug_frames_0, __stop_bug_frames_0 },
+        { __start_bug_frames_1, __stop_bug_frames_1 },
+        { __start_bug_frames_2, __stop_bug_frames_2 },
+        { __start_bug_frames_3, __stop_bug_frames_3 },
+    },
 };
 
 /*
@@ -133,31 +153,6 @@ void __init unregister_init_virtual_region(void)
 void __init setup_virtual_regions(const struct exception_table_entry *start,
                                   const struct exception_table_entry *end)
 {
-    size_t sz;
-    unsigned int i;
-    static const struct bug_frame *const __initconstrel bug_frames[] = {
-        __start_bug_frames,
-        __stop_bug_frames_0,
-        __stop_bug_frames_1,
-        __stop_bug_frames_2,
-        __stop_bug_frames_3,
-        NULL
-    };
-
-    for ( i = 1; bug_frames[i]; i++ )
-    {
-        const struct bug_frame *s;
-
-        s = bug_frames[i - 1];
-        sz = bug_frames[i] - s;
-
-        core.frame[i - 1].n_bugs = sz;
-        core.frame[i - 1].bugs = s;
-
-        core_init.frame[i - 1].n_bugs = sz;
-        core_init.frame[i - 1].bugs = s;
-    }
-
     core_init.ex = core.ex = start;
     core_init.ex_end = core.ex_end = end;
 

xen/include/xen/bug.h

@@ -155,12 +155,6 @@ int do_bug_frame(const struct cpu_user_regs *regs, unsigned long pc);
 
 #endif /* CONFIG_GENERIC_BUG_FRAME */
 
-extern const struct bug_frame __start_bug_frames[],
-                              __stop_bug_frames_0[],
-                              __stop_bug_frames_1[],
-                              __stop_bug_frames_2[],
-                              __stop_bug_frames_3[];
-
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __XEN_BUG_H__ */

xen/include/xen/virtual_region.h

@@ -29,8 +29,7 @@ struct virtual_region
     symbols_lookup_t *symbols_lookup;
 
     struct {
-        const struct bug_frame *bugs; /* The pointer to array of bug frames. */
-        size_t n_bugs;          /* The number of them. */
+        const struct bug_frame *start, *stop; /* Pointers to array of bug frames. */
     } frame[BUGFRAME_NR];
 
     const struct exception_table_entry *ex;

xen/include/xen/xen.lds.h

@@ -115,13 +115,19 @@
 /* List of constructs other than *_SECTIONS in alphabetical order. */
 
 #define BUGFRAMES                               \
-    __start_bug_frames = .;                     \
+    __start_bug_frames_0 = .;                   \
     *(.bug_frames.0)                            \
     __stop_bug_frames_0 = .;                    \
+                                                \
+    __start_bug_frames_1 = .;                   \
     *(.bug_frames.1)                            \
     __stop_bug_frames_1 = .;                    \
+                                                \
+    __start_bug_frames_2 = .;                   \
     *(.bug_frames.2)                            \
     __stop_bug_frames_2 = .;                    \
+                                                \
+    __start_bug_frames_3 = .;                   \
     *(.bug_frames.3)                            \
     __stop_bug_frames_3 = .;