On 2/8/25 1:02 AM, Andrew Cooper wrote:
Right now, run_in_exception_handler() takes an input in an arbitrary register,
and clobbers BUG_FN_REG. This causes the compiler to calculate fn in the
wrong regsiter.
Probably, we should give a chance for the patch which suggests to use
GENERIC_BUG_FRAME:
https://lore.kernel.org/xen-devel/8fdb98350ae4fc6029738d0aabe13a57e1945a50.1680086655.git.oleksii.kuroc...@gmail.com/
~ Oleksii
Instead, use `register asm()` which is the normal way of tying register
constraints to exact registers.
Bloat-o-meter reports:
ARM64:
Function old new delta
dump_registers 356 348 -8
ARM32:
ns16550_poll 52 48 -4
dump_registers 432 428 -4
The other instruction dropped in ARM64's dump_registers() is an alignment nop.
No functional change.
Signed-off-by: Andrew Cooper<[email protected]>
----
CC: Stefano Stabellini<[email protected]>
CC: Julien Grall<[email protected]>
CC: Volodymyr Babchuk<[email protected]>
CC: Bertrand Marquis<[email protected]>
CC: Michal Orzel<[email protected]>
CC: Oleksii Kurochko<[email protected]>
---
xen/arch/arm/include/asm/bug.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/xen/arch/arm/include/asm/bug.h b/xen/arch/arm/include/asm/bug.h
index cacaf014ab09..8bf71587bea1 100644
--- a/xen/arch/arm/include/asm/bug.h
+++ b/xen/arch/arm/include/asm/bug.h
@@ -59,15 +59,15 @@ struct bug_frame {
* be called function in a fixed register.
*/
#define run_in_exception_handler(fn) do { \
- asm ("mov " __stringify(BUG_FN_REG) ", %0\n" \
- "1:"BUG_INSTR"\n" \
+ register unsigned long _fn asm (STR(BUG_FN_REG)) = (unsigned long)(fn); \
+ asm ("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) ); \
+ ".popsection" :: "r" (_fn) ); \
} while (0)
#define WARN() BUG_FRAME(BUGFRAME_warn, __LINE__, __FILE__, 0, "")
