sys_ni: Fix cond_syscall() alias for LTO

When using LTO, the conditional syscall aliases aren't weak, and instead
override implemented syscalls rather than serve as a fallback for
missing syscalls. Fix the cond_syscall() alias using an attribute so
that it gets properly evaluated at link time.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: Yousef Algadri <yusufgadrie@gmail.com>
Change-Id: I3c13715855843178ae7590814bb785037ae041c0
Signed-off-by: Panchajanya Sarkar <panchajanya@azure-dev.live>
Signed-off-by: UtsavBalar1231 <utsavbalar1231@gmail.com>

include/linux/linkage.h

@@ -23,10 +23,8 @@
 #endif
 
 #ifndef cond_syscall
-#define cond_syscall(x)	asm(				\
-	".weak " VMLINUX_SYMBOL_STR(x) "\n\t"		\
-	".set  " VMLINUX_SYMBOL_STR(x) ","		\
-		 VMLINUX_SYMBOL_STR(sys_ni_syscall))
+#define cond_syscall(x) \
+	long __attribute__((weak, alias("sys_ni_syscall"))) x(void);
 #endif
 
 #ifndef SYSCALL_ALIAS

kernel/Makefile

@@ -32,9 +32,6 @@ KCOV_INSTRUMENT_kcov.o := n
 KASAN_SANITIZE_kcov.o := n
 CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
-# cond_syscall is currently not LTO compatible
-CFLAGS_sys_ni.o = $(DISABLE_LTO)
-
 # Don't instrument error handlers
 CFLAGS_cfi.o = $(DISABLE_CFI_CLANG)