linux-kernel - Re: [RFC PATCH 13/12] Retpoline vs. CONFIG_TRIM_UNUSED

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Message-ID: <1515312191.29312.299.camel@infradead.org>
Date:   Sun, 07 Jan 2018 08:03:11 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>,
        "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
        "hongjiu.lu@...el.com" <hongjiu.lu@...el.com>,
        "Tsimbalist, Igor V" <igor.v.tsimbalist@...el.com>
Cc:     Paul Turner <pjt@...gle.com>, LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [RFC PATCH 13/12] Retpoline vs. CONFIG_TRIM_UNUSED_SYMBOLS

On Sun, 2018-01-07 at 00:10 +0000, David Woodhouse wrote:
> Arjan pointed out that CONFIG_TRIM_UNUSED_SYMBOLS *really* doesn't like
> the dot in the symbols that GCC uses for the thunks.
> 
> This seems to work, although my eyes are bleeding just a little bit.
> 
> Given this, and the hack we already needed for MODVERSIONS, I wonder if
> a better approach might be to export the thunks using underscores in
> place of the dots, which is a relatively simple abuse of
> __EXPORT_SYMBOL(__x86_indirect_thunk_foo,__x86.indirect_thunk.foo,),
> and then have a hack either when generating or loading modules to do
> the same replacement.

Alternatively, and much simpler... HJ (or Igor), please can we change
the GCC patches so that the __x86.indirect_thunk.rxx symbols don't have
those awful dots in them? They are causing *lots* of pain.

Or we could build *modules* with the inline thunk and lose the ability
to ALTERNATIVE it away, I suppose.

> diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
> index ccb117a4588b..64d7a45ea954 100644
> --- a/arch/x86/lib/retpoline.S
> +++ b/arch/x86/lib/retpoline.S
> @@ -8,7 +8,13 @@
>  #include 
>  #include 
>  
> -.macro THUNK reg
> +#ifdef CONFIG_TRIM_UNUSED_KSYMS
> +#define EXPORT_REG(reg) __is_defined(__KSYM___x86_indirect_thunk_ ## reg)
> +#else
> +#define EXPORT_REG(reg)	1
> +#endif
> +
> +.macro THUNK reg export
>  	.section .text.__x86.indirect_thunk.\reg
>  
>  ENTRY(__x86.indirect_thunk.\reg)
> @@ -16,15 +22,33 @@ ENTRY(__x86.indirect_thunk.\reg)
>  	NOSPEC_JMP %\reg
>  	CFI_ENDPROC
>  ENDPROC(__x86.indirect_thunk.\reg)
> -EXPORT_SYMBOL(__x86.indirect_thunk.\reg)
> +
> +.if \export
> +	EXPORT_SYMBOL_FORCE(__x86.indirect_thunk.\reg)
> +.endif
>  .endm
>  
> -#ifdef CONFIG_64BIT
> -.irp reg rax rbx rcx rdx rsi rdi rbp r8 r9 r10 r11 r12 r13 r14 r15
> -	THUNK \reg
> -.endr
> +#ifdef __KSYM_DEPS__
> +#define GENERATE_THUNK(reg) EXPORT_SYMBOL(__x86.indirect_thunk. ## reg)
>  #else
> -.irp reg eax ebx ecx edx esi edi ebp
> -	THUNK \reg
> -.endr
> +#define GENERATE_THUNK(reg) THUNK reg EXPORT_REG(reg)
> +#endif
> +
> +GENERATE_THUNK(_ASM_AX)
> +GENERATE_THUNK(_ASM_BX)
> +GENERATE_THUNK(_ASM_CX)
> +GENERATE_THUNK(_ASM_DX)
> +GENERATE_THUNK(_ASM_SI)
> +GENERATE_THUNK(_ASM_DI)
> +GENERATE_THUNK(_ASM_BP)
> +GENERATE_THUNK(_ASM_SP)
> +#ifdef CONFIG_64BIT
> +GENERATE_THUNK(r8)
> +GENERATE_THUNK(r9)
> +GENERATE_THUNK(r10)
> +GENERATE_THUNK(r11)
> +GENERATE_THUNK(r12)
> +GENERATE_THUNK(r13)
> +GENERATE_THUNK(r14)
> +GENERATE_THUNK(r15)
>  #endif
> diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
> index 719db1968d81..b13bb65e2530 100644
> --- a/include/asm-generic/export.h
> +++ b/include/asm-generic/export.h
> @@ -63,33 +63,33 @@ KSYM(__kcrctab_\name):
>  
>  #if defined(__KSYM_DEPS__)
>  
> -#define __EXPORT_SYMBOL(sym, val, sec)	=== __KSYM_##sym ===
> +#define __EXPORT_SYMBOL(sym, val, sec, force)	=== __KSYM_##sym ===
>  
>  #elif defined(CONFIG_TRIM_UNUSED_KSYMS)
>  
>  #include 
>  #include 
>  
> -#define __EXPORT_SYMBOL(sym, val, sec)				\
> -	__cond_export_sym(sym, val, sec, __is_defined(__KSYM_##sym))
> +#define __EXPORT_SYMBOL(sym, val, sec, force)			\
> +	 __cond_export_sym(sym, val, sec, __or(force, __is_defined(__KSYM_##sym)))
>  #define __cond_export_sym(sym, val, sec, conf)			\
>  	___cond_export_sym(sym, val, sec, conf)
>  #define ___cond_export_sym(sym, val, sec, enabled)		\
>  	__cond_export_sym_##enabled(sym, val, sec)
>  #define __cond_export_sym_1(sym, val, sec) ___EXPORT_SYMBOL sym, val, sec
>  #define __cond_export_sym_0(sym, val, sec) /* nothing */
> -
>  #else
> -#define __EXPORT_SYMBOL(sym, val, sec) ___EXPORT_SYMBOL sym, val, sec
> +#define __EXPORT_SYMBOL(sym, val, sec, force)	___EXPORT_SYMBOL sym, val, sec
>  #endif
>  
>  #define EXPORT_SYMBOL(name)					\
> -	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)),)
> +	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)), , 0)
>  #define EXPORT_SYMBOL_GPL(name) 				\
> -	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)), _gpl)
> +	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)), _gpl, 0)
>  #define EXPORT_DATA_SYMBOL(name)				\
> -	__EXPORT_SYMBOL(name, KSYM(name),)
> +	__EXPORT_SYMBOL(name, KSYM(name), , 0)
>  #define EXPORT_DATA_SYMBOL_GPL(name)				\
> -	__EXPORT_SYMBOL(name, KSYM(name),_gpl)
> -
> +	__EXPORT_SYMBOL(name, KSYM(name), _gpl, 0)
> +#define EXPORT_SYMBOL_FORCE(name)				\
> +	__EXPORT_SYMBOL(name, KSYM(name), , 1)
>  #endif
> diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh
> index 513da1a4a2da..991cd136291b 100755
> --- a/scripts/adjust_autoksyms.sh
> +++ b/scripts/adjust_autoksyms.sh
> @@ -60,7 +60,7 @@ cat > "$new_ksyms_file" << EOT
>  
>  EOT
>  [ "$(ls -A "$MODVERDIR")" ] &&
> -sed -ns -e '3{s/ /\n/g;/^$/!p;}' "$MODVERDIR"/*.mod | sort -u |
> +sed -ns -e '3{s/ /\n/g;/^$/!p;}' "$MODVERDIR"/*.mod | sort -u | tr . _ |
>  while read sym; do
>  	if [ -n "$CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX" ]; then
>  		sym="${sym#_}"
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