On 10/03/2023 10:07, Jiri Olsa wrote:
> hi,
> with latest pahole fixes we get rid of some syscall functions (with
> __x64_sys_ prefix) and it seems to fall down to 2 cases:
>
> - weak syscall functions generated in kernel/sys_ni.c prevent these syscalls
> to be generated in BTF. The reason is the __COND_SYSCALL macro uses
> '__unused' for regs argument:
>
> #define __COND_SYSCALL(abi, name) \
> __weak long __##abi##_##name(const struct pt_regs *__unused); \
> __weak long __##abi##_##name(const struct pt_regs *__unused) \
> { \
> return sys_ni_syscall(); \
> }
>
> and having weak function with different argument name will rule out the
> syscall from BTF functions
>
> the patch below workarounds this by using the same argument name,
> but I guess the real fix would be to check the whole type not just
> the argument name.. or ignore weak function if there's non weak one
>
> I guess there will be more cases like this in kernel
>
>
Thanks for the report Jiri! I'm working on reusing the dwarves_fprintf.c
code to use string comparisons of function prototypes (minus parameter names!)
instead as a more robust comparison. Hope to have something working soon..
> - we also do not get any syscall with no arguments, because they are
> generated as aliases to __do_<syscall> function:
>
> $ nm ./vmlinux | grep _sys_fork
> ffffffff81174890 t __do_sys_fork
> ffffffff81174890 T __ia32_sys_fork
> ffffffff81174880 T __pfx___x64_sys_fork
> ffffffff81174890 T __x64_sys_fork
>
> with:
> #define __SYS_STUB0(abi, name) \
> long __##abi##_##name(const struct pt_regs *regs); \
> ALLOW_ERROR_INJECTION(__##abi##_##name, ERRNO); \
> long __##abi##_##name(const struct pt_regs *regs) \
> __alias(__do_##name);
>
> the problem seems to be that there's no DWARF data for aliased symbol,
> so pahole won't see any __x64_sys_fork record
> I'm not sure how to fix this one
>
Is this one a new issue, or did you just spot it when looking at the other case?
Thanks!
Alan
> technically we can always connect to __do_sys_fork, but we'd need to
> have special cases for such syscalls.. would be great to have all with
> '__x64_sys_' prefix
>
>
> thoughts?
>
> thanks,
> jirka
>
>
> ---
> diff --git a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
> index fd2669b1cb2d..e02dab630577 100644
> --- a/arch/x86/include/asm/syscall_wrapper.h
> +++ b/arch/x86/include/asm/syscall_wrapper.h
> @@ -80,8 +80,8 @@ extern long __ia32_sys_ni_syscall(const struct pt_regs *regs);
> }
>
> #define __COND_SYSCALL(abi, name) \
> - __weak long __##abi##_##name(const struct pt_regs *__unused); \
> - __weak long __##abi##_##name(const struct pt_regs *__unused) \
> + __weak long __##abi##_##name(const struct pt_regs *regs); \
> + __weak long __##abi##_##name(const struct pt_regs *regs) \
> { \
> return sys_ni_syscall(); \
> }
>
