Hi Juergen,
On 16/01/2021 10:33, Juergen Gross wrote:
Add support to run a function in an exception handler for Arm. Do it
as on x86 via a bug_frame, but pass the function pointer via a
register (this needs to be done that way, because inline asm support
for 32-bit Arm lacks the needed functionality to reference an
arbitrary function via the bugframe).
I was going to commit the series, but then realized the commit message
and comment needs some tweaking because technically GCC is supporting
'i' (I managed to get it working with -fno-pie).
So how about:
"This is needed to be done that way because GCC complains about invalid
constraint when using a function pointer with "i" and PIE is enabled
(default on most of GCC shipped with distro). Clang happily accepts it,
so it may be a bug in GCC."
+/*
+ * Unfortunately gcc for arm 32-bit doesn't support the "i" constraint, so
+ * the easiest way to implement run_in_exception_handler() is to pass the
+ * to be called function in a fixed register.
+ */
This comment should also be updated.
I can update both while committing if you are happy with the change.
+#define run_in_exception_handler(fn) do { \
+ asm ("mov " __stringify(BUG_FN_REG) ", %0\n" \
+ "1:"BUG_INSTR"\n" \
+ ".pushsection .bug_frames." __stringify(BUGFRAME_run_fn) "," \
+ " \"a\", %%progbits\n" \
+ "2:\n" \
+ ".p2align 2\n" \
+ ".long (1b - 2b)\n" \
+ ".long 0, 0, 0\n" \
+ ".popsection" :: "r" (fn) : __stringify(BUG_FN_REG) ); \
+} while (0)
+
#define WARN() BUG_FRAME(BUGFRAME_warn, __LINE__, __FILE__, 0, "")
#define BUG() do { \
@@ -73,7 +91,8 @@ struct 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_2[],
+ __stop_bug_frames_3[];
#endif /* __ARM_BUG_H__ */
/*
Cheers,
--
Julien Grall
