start_kernel: Omit prevent_tail_call_optimization() for newer toolchains

prevent_tail_call_optimization() was added in
commit a9a3ed1eff36 ("x86: Fix early boot crash on gcc-10, third try")
to work around stack canaries getting inserted into functions that would
initialize the stack canary in the first place.

Now that we have no_stack_protector function attribute (gcc-11+,
clang-7+) and use it on start_kernel(), remove the call to
prevent_tail_call_optimization() such that we may one day remove it
outright.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20230412-no_stackp-v2-2-116f9fe4bbe7@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

diff --git a/init/main.c b/init/main.c
index c445c1fb19b95569071976a0b1d4398d834d94a8..c0b6499c31db393ba2ad7e122148bdd5e0aaea47 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -1088,7 +1088,13 @@ void start_kernel(void)
        /* Do the rest non-__init'ed, we're now alive */
        arch_call_rest_init();
 
+       /*
+        * Avoid stack canaries in callers of boot_init_stack_canary for gcc-10
+        * and older.
+        */
+#if !__has_attribute(__no_stack_protector__)
        prevent_tail_call_optimization();
+#endif
 }
 
 /* Call all constructor functions linked into the kernel. */