Re: [PATCH 05/22] kbuild: lto: postpone objtool

Peter Zijlstra
2020-06-24T21:19:35Z

On Wed, Jun 24, 2020 at 01:31:43PM -0700, Sami Tolvanen wrote:
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 30827f82ad62..12b115152532 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -120,7 +120,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> /* Annotate a C jump table to allow objtool to follow the code flow */
> #define __annotate_jump_table __section(.rodata..c_jump_table)
>
> -#ifdef CONFIG_DEBUG_ENTRY
> +#if defined(CONFIG_DEBUG_ENTRY) || defined(CONFIG_LTO_CLANG)
> /* Begin/end of an instrumentation safe region */
> #define instrumentation_begin() ({ \
> asm volatile("%c0:\n\t" \

Why would you be doing noinstr validation for lto builds? That doesn't
make sense.

> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 9ad9210d70a1..9fdba71c135a 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -399,7 +399,7 @@ config STACK_VALIDATION
>
> config VMLINUX_VALIDATION
> bool
> - depends on STACK_VALIDATION && DEBUG_ENTRY && !PARAVIRT
> + depends on STACK_VALIDATION && (DEBUG_ENTRY || LTO_CLANG) && !PARAVIRT
> default y
>

For that very same reason you shouldn't be excluding paravirt either.

> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index d168f0cfe67c..9f1df2f1fab5 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -48,6 +48,21 @@ endif # CC_USING_PATCHABLE_FUNCTION_ENTRY
> endif # CC_USING_RECORD_MCOUNT
> endif # CONFIG_FTRACE_MCOUNT_RECORD
>
> +ifdef CONFIG_STACK_VALIDATION
> +ifneq ($(SKIP_STACK_VALIDATION),1)
> +cmd_ld_ko_o += \
> + $(objtree)/tools/objtool/objtool \
> + $(if $(CONFIG_UNWINDER_ORC),orc generate,check) \
> + --module \
> + $(if $(CONFIG_FRAME_POINTER),,--no-fp) \
> + $(if $(CONFIG_GCOV_KERNEL),--no-unreachable,) \
> + $(if $(CONFIG_RETPOLINE),--retpoline,) \
> + $(if $(CONFIG_X86_SMAP),--uaccess,) \
> + $(@:.ko=$(prelink-ext).o);
> +
> +endif # SKIP_STACK_VALIDATION
> +endif # CONFIG_STACK_VALIDATION

What about the objtool invocation from link-vmlinux.sh ?