[PATCH v5 1/3] xen/arm: add support for run_in_exception_handler()

[Juergen Gross <jgross@xxxxxxxx>]

Add support to run a function in an exception handler for Arm. Do it
the same way as on x86 via a bug_frame.

Use the same BUGFRAME_* #defines as on x86 in order to make a future
common header file more easily achievable.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V4:
- new patch

V5:
- adjust BUG_FRAME() macro (Jan Beulich)
- adjust arm linker script (Jan Beulich)
- drop #ifdef x86 in common/virtual_region.c

I have verified the created bugframes are correct by inspecting the
created binary.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/arm/traps.c        | 10 ++++++++-
 xen/arch/arm/xen.lds.S      |  2 ++
 xen/common/virtual_region.c |  2 --
 xen/include/asm-arm/bug.h   | 45 +++++++++++++++++--------------------
 4 files changed, 32 insertions(+), 27 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 22bd1bd4c6..912b9a3d77 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1236,8 +1236,16 @@ int do_bug_frame(const struct cpu_user_regs *regs, 
vaddr_t pc)
     if ( !bug )
         return -ENOENT;
 
+    if ( id == BUGFRAME_run_fn )
+    {
+        void (*fn)(const struct cpu_user_regs *) = bug_ptr(bug);
+
+        fn(regs);
+        return 0;
+    }
+
     /* WARN, BUG or ASSERT: decode the filename pointer and line number. */
-    filename = bug_file(bug);
+    filename = bug_ptr(bug);
     if ( !is_kernel(filename) )
         return -EINVAL;
     fixup = strlen(filename);
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 6342ac4ead..004b182acb 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -49,6 +49,8 @@ SECTIONS
        __stop_bug_frames_1 = .;
        *(.bug_frames.2)
        __stop_bug_frames_2 = .;
+       *(.bug_frames.3)
+       __stop_bug_frames_3 = .;
        *(.rodata)
        *(.rodata.*)
        *(.data.rel.ro)
diff --git a/xen/common/virtual_region.c b/xen/common/virtual_region.c
index 4fbc02e35a..30b0b4ab9c 100644
--- a/xen/common/virtual_region.c
+++ b/xen/common/virtual_region.c
@@ -123,9 +123,7 @@ void __init setup_virtual_regions(const struct 
exception_table_entry *start,
         __stop_bug_frames_0,
         __stop_bug_frames_1,
         __stop_bug_frames_2,
-#ifdef CONFIG_X86
         __stop_bug_frames_3,
-#endif
         NULL
     };
 
diff --git a/xen/include/asm-arm/bug.h b/xen/include/asm-arm/bug.h
index 36c803357c..4610835ac3 100644
--- a/xen/include/asm-arm/bug.h
+++ b/xen/include/asm-arm/bug.h
@@ -15,65 +15,62 @@
 
 struct bug_frame {
     signed int loc_disp;    /* Relative address to the bug address */
-    signed int file_disp;   /* Relative address to the filename */
+    signed int ptr_disp;    /* Relative address to the filename or function */
     signed int msg_disp;    /* Relative address to the predicate (for ASSERT) 
*/
     uint16_t line;          /* Line number */
     uint32_t pad0:16;       /* Padding for 8-bytes align */
 };
 
 #define bug_loc(b) ((const void *)(b) + (b)->loc_disp)
-#define bug_file(b) ((const void *)(b) + (b)->file_disp);
+#define bug_ptr(b) ((const void *)(b) + (b)->ptr_disp);
 #define bug_line(b) ((b)->line)
 #define bug_msg(b) ((const char *)(b) + (b)->msg_disp)
 
-#define BUGFRAME_warn   0
-#define BUGFRAME_bug    1
-#define BUGFRAME_assert 2
+#define BUGFRAME_run_fn 0
+#define BUGFRAME_warn   1
+#define BUGFRAME_bug    2
+#define BUGFRAME_assert 3
 
-#define BUGFRAME_NR     3
+#define BUGFRAME_NR     4
 
 /* Many versions of GCC doesn't support the asm %c parameter which would
  * be preferable to this unpleasantness. We use mergeable string
  * sections to avoid multiple copies of the string appearing in the
  * Xen image.
  */
-#define BUG_FRAME(type, line, file, has_msg, msg) do {                      \
+#define BUG_FRAME(type, line, ptr, msg) do {                                \
     BUILD_BUG_ON((line) >> 16);                                             \
     BUILD_BUG_ON((type) >= BUGFRAME_NR);                                    \
     asm ("1:"BUG_INSTR"\n"                                                  \
-         ".pushsection .rodata.str, \"aMS\", %progbits, 1\n"                \
-         "2:\t.asciz " __stringify(file) "\n"                               \
-         "3:\n"                                                             \
-         ".if " #has_msg "\n"                                               \
-         "\t.asciz " #msg "\n"                                              \
-         ".endif\n"                                                         \
-         ".popsection\n"                                                    \
-         ".pushsection .bug_frames." __stringify(type) ", \"a\", %progbits\n"\
-         "4:\n"                                                             \
+         ".pushsection .bug_frames." __stringify(type) ", \"a\", %%progbits\n"\
+         "2:\n"                                                             \
          ".p2align 2\n"                                                     \
-         ".long (1b - 4b)\n"                                                \
-         ".long (2b - 4b)\n"                                                \
-         ".long (3b - 4b)\n"                                                \
+         ".long (1b - 2b)\n"                                                \
+         ".long (%0 - 2b)\n"                                                \
+         ".long (%1 - 2b)\n"                                                \
          ".hword " __stringify(line) ", 0\n"                                \
-         ".popsection");                                                    \
+         ".popsection" :: "i" (ptr), "i" (msg));                            \
 } while (0)
 
-#define WARN() BUG_FRAME(BUGFRAME_warn, __LINE__, __FILE__, 0, "")
+#define run_in_exception_handler(fn) BUG_FRAME(BUGFRAME_run_fn, 0, fn, "")
+
+#define WARN() BUG_FRAME(BUGFRAME_warn, __LINE__, __FILE__, "")
 
 #define BUG() do {                                              \
-    BUG_FRAME(BUGFRAME_bug,  __LINE__, __FILE__, 0, "");        \
+    BUG_FRAME(BUGFRAME_bug,  __LINE__, __FILE__, "");           \
     unreachable();                                              \
 } while (0)
 
 #define assert_failed(msg) do {                                 \
-    BUG_FRAME(BUGFRAME_assert, __LINE__, __FILE__, 1, msg);     \
+    BUG_FRAME(BUGFRAME_assert, __LINE__, __FILE__, msg);        \
     unreachable();                                              \
 } while (0)
 
 extern const struct bug_frame __start_bug_frames[],
                               __stop_bug_frames_0[],
                               __stop_bug_frames_1[],
-                              __stop_bug_frames_2[];
+                              __stop_bug_frames_2[],
+                              __stop_bug_frames_3[];
 
 #endif /* __ARM_BUG_H__ */
 /*
-- 
2.26.2