Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for data

Jiri Slaby
2017-03-22T15:01:08Z

On 03/22/2017, 03:11 PM, Josh Poimboeuf wrote:
> Or, here's a much easier way to do it, without involving objtool:
>
> --- a/include/linux/linkage.h
> +++ b/include/linux/linkage.h
> @@ -138,9 +138,17 @@
> name:
> #endif
>
> +#ifndef CHECK_DUP_SYM_END
> +#define CHECK_DUP_SYM_END(name) \
> + .pushsection .discard.sym_func_end ASM_NL \
> + SYM_END_##name: .byte 0 ASM_NL \
> + .popsection
> +#endif
> +
> /* SYM_END -- use only if you have to */
> #ifndef SYM_END
> #define SYM_END(name, sym_type) \
> + CHECK_DUP_SYM_END(name) ASM_NL \
> .type name sym_type ASM_NL \
> .size name, .-name
> #endif

I tried this approach and it didn't work for me inside .macros. Oh,
well, the name cannot be first, so now, we can have a check for both
correct pairing _and_ duplicate ends in one:

#define SYM_CHECK_START(name) \
.pushsection .rodata.bubak ASM_NL \
.long has_no_SYM_END_##name - . ASM_NL \
.popsection

#define SYM_CHECK_END(name) \
has_no_SYM_END_##name:

/* SYM_START -- use only if you have to */
#ifndef SYM_START
#define SYM_START(name, align, visibility, entry) \
SYM_CHECK_START(name) ASM_NL \
visibility(name) ASM_NL \
align ASM_NL \
name: ASM_NL \
entry
#endif

/* SYM_END -- use only if you have to */
#ifndef SYM_END
#define SYM_END(name, sym_type, exit) \
exit ASM_NL \
SYM_CHECK_END(name) ASM_NL \
.type name sym_type ASM_NL \
.size name, .-name
#endif

So for the ftrace mistake I did:

AS arch/x86/kernel/mcount_64.o
/home/latest/linux/arch/x86/kernel/mcount_64.S: Assembler messages:
/home/latest/linux/arch/x86/kernel/mcount_64.S:192: Error: symbol
`has_no_SYM_END_ftrace_caller' is already defined

or if I remove SYM_END_FUNC completely:
LD vmlinux.o
MODPOST vmlinux.o
arch/x86/built-in.o:(.rodata.bubak+0x130): undefined reference to
`has_no_SYM_END_ftrace_stub'

Sad is that this occurs only during linking, so I cannot put it in the
.discard section -- ideas?

thanks,
--
js
suse labs