[PATCH 3/3] arm: smh: Allow semihosting trap calls to be inlined

[Andre Przywara]

Currently our semihosting trap function is somewhat fragile: we rely
on the current compiler behaviour to assign the second inline assembly
argument to the next free register (r1/x1), which happens to be the
"addr" argument to the smh_trap() function (per the calling convention).
I guess this is also the reason for the noinline attribute.

Make it explicit what we want: the "addr" argument needs to go into r1,
so we add another register variable. This allows to drop the "noinline"
attribute, so now the compiler beautifully inlines just the trap
instruction directly into the calling function.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
---
 arch/arm/lib/semihosting.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm/lib/semihosting.c b/arch/arm/lib/semihosting.c
index 3dee7d51b36..939c0f75132 100644
--- a/arch/arm/lib/semihosting.c
+++ b/arch/arm/lib/semihosting.c
@@ -39,9 +39,10 @@
 /*
  * Call the handler
  */
-static noinline long smh_trap(unsigned int sysnum, void *addr)
+static long smh_trap(unsigned int sysnum, void *addr)
 {
 	register long result asm("r0");
+	register void *_addr asm("r1") = addr;
 
 	/*
 	 * We need a memory clobber (aka compiler barrier) for two reasons:
@@ -53,7 +54,7 @@ static noinline long smh_trap(unsigned int sysnum, void *addr)
 	 */
 	asm volatile (SMH_TRAP
 		      : "=r" (result)
-		      : "0"(sysnum), "r"(USE_PTR(addr))
+		      : "0"(sysnum), "r"(USE_PTR(_addr))
 		      : "memory");
 
 	return result;
-- 
2.25.1