Hi,
On 08/02/2025 00:02, 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.
Just to confirm, you mean, the compiler is not clever enough to notice
that the value should be in the register BUG_FN_REG and therefore, two
registers will be clobbered. Is that correct?
> > 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, "")
--
Julien Grall
