Re: [PATCH] ftrace: x86: Fix a compile error about get_kernel_nofault()

Gabriel de Perthuis
2025-02-06T18:20:12Z

Hello,
I can confirm this solves the build issue alongside gendwarfksyms;
much appreciated.

Le jeu. 6 févr. 2025 à 04:12, Masami Hiramatsu (Google)
<mhiramat@kernel.org> a écrit :
>
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> Fix a compile error about get_kernel_nofault() which is defined in the
> linux/uaccess.h. Since asm/ftrace.h is widely used, including
> linux/uaccess.h in asm/ftrace.h caused another error. Thus this
> moves arch_ftrace_get_symaddr() into arch/x86/kernel/ftrace.c.
>
> The original errors look like:
>
> In file included from ./arch/x86/include/asm/asm-prototypes.h:2,
> from <stdin>:3:
> ./arch/x86/include/asm/ftrace.h: In function 'arch_ftrace_get_symaddr':
> ./arch/x86/include/asm/ftrace.h:46:21: error: implicit declaration of function 'get_kernel_nofault' [-Werror=implicit-function-declaration]
> 46 | if (get_kernel_nofault(instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE)))
> | ^~~~~~~~~~~~~~~~~~
>
> This also makes ftrace_get_symaddr() available only when
> CONFIG_HAVE_FENTRY=y on x86.
>
> Reported-by: Gabriel de Perthuis <g2p.code@gmail.com>
> Closes: https://lore.kernel.org/all/a87f98bf-45b1-4ef5-aa77-02f7e61203f4@gmail.com/
> Reported-by: Haiyue Wang <haiyuewa@163.com>
> Closes: https://lore.kernel.org/all/20250205180116.88644-1-haiyuewa@163.com/
> Fixes: 2bc56fdae1ba ("ftrace: Add ftrace_get_symaddr to convert fentry_ip to symaddr")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
> arch/x86/include/asm/ftrace.h | 23 ++++-------------------
> arch/x86/kernel/ftrace.c | 26 +++++++++++++++++++++++++-
> 2 files changed, 29 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index f9cb4d07df58..1ed08f2de366 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -34,26 +34,11 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
> return addr;
> }
>
> -static inline unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
> -{
> -#ifdef CONFIG_X86_KERNEL_IBT
> - u32 instr;
> -
> - /* We want to be extra safe in case entry ip is on the page edge,
> - * but otherwise we need to avoid get_kernel_nofault()'s overhead.
> - */
> - if ((fentry_ip & ~PAGE_MASK) < ENDBR_INSN_SIZE) {
> - if (get_kernel_nofault(instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE)))
> - return fentry_ip;
> - } else {
> - instr = *(u32 *)(fentry_ip - ENDBR_INSN_SIZE);
> - }
> - if (is_endbr(instr))
> - fentry_ip -= ENDBR_INSN_SIZE;
> -#endif
> - return fentry_ip;
> -}
> +/* This does not support mcount. */
> +#ifdef CONFIG_HAVE_FENTRY
> +unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip);
> #define ftrace_get_symaddr(fentry_ip) arch_ftrace_get_symaddr(fentry_ip)
> +#endif
>
> #ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
>
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 166bc0ea3bdf..7250118005fc 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -29,11 +29,35 @@
>
> #include <trace/syscall.h>
>
> -#include <asm/kprobes.h>
> #include <asm/ftrace.h>
> +#include <asm/ibt.h>
> +#include <asm/kprobes.h>
> #include <asm/nops.h>
> #include <asm/text-patching.h>
>
> +#ifdef CONFIG_HAVE_FENTRY
> +/* Convert fentry address to the symbol address. */
> +unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
> +{
> +#ifdef CONFIG_X86_KERNEL_IBT
> + u32 instr;
> +
> + /* We want to be extra safe in case entry ip is on the page edge,
> + * but otherwise we need to avoid get_kernel_nofault()'s overhead.
> + */
> + if ((fentry_ip & ~PAGE_MASK) < ENDBR_INSN_SIZE) {
> + if (get_kernel_nofault(instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE)))
> + return fentry_ip;
> + } else {
> + instr = *(u32 *)(fentry_ip - ENDBR_INSN_SIZE);
> + }
> + if (is_endbr(instr))
> + fentry_ip -= ENDBR_INSN_SIZE;
> +#endif
> + return fentry_ip;
> +}
> +#endif
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
>
> static int ftrace_poke_late = 0;
>