[tip: objtool/core] start_kernel: Omit prevent_tail_call_optimization() for newer toolchains

[tip-bot2 for ndesaulniers@xxxxxxxxxx]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     dc1d05536f44cee16e46e86316e6718b2c0d8872
Gitweb:        https://git.kernel.org/tip/dc1d05536f44cee16e46e86316e6718b2c0d8872
Author:        ndesaulniers@xxxxxxxxxx <ndesaulniers@xxxxxxxxxx>
AuthorDate:    Mon, 17 Apr 2023 15:00:06 -07:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Tue, 16 May 2023 06:28:24 -07:00

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@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230412-no_stackp-v2-2-116f9fe4bbe7@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 init/main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/init/main.c b/init/main.c
index c445c1f..c0b6499 100644
--- 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. */