linux-kernel - Re: [PATCH] x86/syscalls: shrink entry/syscall

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Message-ID: <8B198413-0C9B-40A2-8478-F22206AAE6FA@zytor.com>
Date: Wed, 27 Dec 2023 15:50:33 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Al Viro <viro@...iv.linux.org.uk>, Tanzir Hasan <tanzirh@...gle.com>
CC: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Nick Desaulniers <nnn@...gle.com>
Subject: Re: [PATCH] x86/syscalls: shrink entry/syscall_32.i via IWYU

On December 27, 2023 3:34:44 PM PST, Al Viro <viro@...iv.linux.org.uk> wrote:
>On Wed, Dec 27, 2023 at 10:38:41PM +0000, Tanzir Hasan wrote:
>> This diff uses an open source tool include-what-you-use (IWYU) to modify
>> the include list, changing indirect includes to direct includes. IWYU is
>> implemented using the IWYUScripts github repository which is a tool that
>> is currently undergoing development. These changes seek to improve build
>> times.
>> 
>> This change to entry/syscall_32.c resulted in a preprocessed size of
>> entry/syscall_32.i from 64002 lines to 47986 lines (-25%) for the x86
>> defconfig.
>>
>> Signed-off-by: Tanzir Hasan <tanzirh@...gle.com>
>> ---
>>  arch/x86/entry/syscall_32.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/arch/x86/entry/syscall_32.c b/arch/x86/entry/syscall_32.c
>> index 8cfc9bc73e7f..66db11fe8a1c 100644
>> --- a/arch/x86/entry/syscall_32.c
>> +++ b/arch/x86/entry/syscall_32.c
>> @@ -4,7 +4,7 @@
>>  #include <linux/linkage.h>
>>  #include <linux/sys.h>
>>  #include <linux/cache.h>
>> -#include <linux/syscalls.h>
>> +#include <linux/ptrace.h>
>>  #include <asm/syscall.h>
>
>Really?  What do we need linux/ptrace.h for?  Because if it's
>struct pt_regs for the generated externs, we might as well have
>just said
>struct pt_regs;
>and that would be it.
>
><digs around a bit>
>
>As the matter of fact, all you need out of those includes is this:
>
>struct pt_regs;
>typedef long (*sys_call_ptr_t)(const struct pt_regs *);
>extern const sys_call_ptr_t sys_call_table[];
>#if defined(CONFIG_X86_32)
>#define ia32_sys_call_table sys_call_table
>#else
>/*
> * These may not exist, but still put the prototypes in so we
> * can use IS_ENABLED().
> */
>extern const sys_call_ptr_t ia32_sys_call_table[];
>extern const sys_call_ptr_t x32_sys_call_table[];
>#endif
>
>That's _it_.  The same goes for syscall_64.c and syscall_x32.c.
>Oh, and lose the __visible/asmlinkage junk in there - none of that
>stuff is used from asm these days.  See the patch below -
>Untested But Should Work(tm):
>
>diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
>index d813160b14d8..5c470806dd08 100644
>--- a/arch/x86/entry/common.c
>+++ b/arch/x86/entry/common.c
>@@ -36,6 +36,8 @@
> #include <asm/syscall.h>
> #include <asm/irq_stack.h>
> 
>+#include "syscall.h"
>+
> #ifdef CONFIG_X86_64
> 
> static __always_inline bool do_syscall_x64(struct pt_regs *regs, int nr)
>diff --git a/arch/x86/entry/syscall.h b/arch/x86/entry/syscall.h
>new file mode 100644
>index 000000000000..7c52df000ae0
>--- /dev/null
>+++ b/arch/x86/entry/syscall.h
>@@ -0,0 +1,13 @@
>+struct pt_regs;
>+typedef long (*sys_call_ptr_t)(const struct pt_regs *);
>+extern const sys_call_ptr_t sys_call_table[];
>+#if defined(CONFIG_X86_32)
>+#define ia32_sys_call_table sys_call_table
>+#else
>+/*
>+ * These may not exist, but still put the prototypes in so we
>+ * can use IS_ENABLED().
>+ */
>+extern const sys_call_ptr_t ia32_sys_call_table[];
>+extern const sys_call_ptr_t x32_sys_call_table[];
>+#endif
>diff --git a/arch/x86/entry/syscall_32.c b/arch/x86/entry/syscall_32.c
>index 8cfc9bc73e7f..a24a8922692f 100644
>--- a/arch/x86/entry/syscall_32.c
>+++ b/arch/x86/entry/syscall_32.c
>@@ -1,11 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0
> /* System call table for i386. */
> 
>-#include <linux/linkage.h>
>-#include <linux/sys.h>
>-#include <linux/cache.h>
>-#include <linux/syscalls.h>
>-#include <asm/syscall.h>
>+#include "syscall.h"
> 
> #ifdef CONFIG_IA32_EMULATION
> #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, compat)
>@@ -20,6 +16,6 @@
> 
> #define __SYSCALL(nr, sym) __ia32_##sym,
> 
>-__visible const sys_call_ptr_t ia32_sys_call_table[] = {
>+const sys_call_ptr_t ia32_sys_call_table[] = {
> #include <asm/syscalls_32.h>
> };
>diff --git a/arch/x86/entry/syscall_64.c b/arch/x86/entry/syscall_64.c
>index be120eec1fc9..81bde061037b 100644
>--- a/arch/x86/entry/syscall_64.c
>+++ b/arch/x86/entry/syscall_64.c
>@@ -1,11 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0
> /* System call table for x86-64. */
> 
>-#include <linux/linkage.h>
>-#include <linux/sys.h>
>-#include <linux/cache.h>
>-#include <linux/syscalls.h>
>-#include <asm/syscall.h>
>+#include "syscall.h"
> 
> #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
> #include <asm/syscalls_64.h>
>@@ -13,6 +9,6 @@
> 
> #define __SYSCALL(nr, sym) __x64_##sym,
> 
>-asmlinkage const sys_call_ptr_t sys_call_table[] = {
>+const sys_call_ptr_t sys_call_table[] = {
> #include <asm/syscalls_64.h>
> };
>diff --git a/arch/x86/entry/syscall_x32.c b/arch/x86/entry/syscall_x32.c
>index bdd0e03a1265..7b5170a99b9a 100644
>--- a/arch/x86/entry/syscall_x32.c
>+++ b/arch/x86/entry/syscall_x32.c
>@@ -1,11 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0
> /* System call table for x32 ABI. */
> 
>-#include <linux/linkage.h>
>-#include <linux/sys.h>
>-#include <linux/cache.h>
>-#include <linux/syscalls.h>
>-#include <asm/syscall.h>
>+#include "syscall.h"
> 
> #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
> #include <asm/syscalls_x32.h>
>@@ -13,6 +9,6 @@
> 
> #define __SYSCALL(nr, sym) __x64_##sym,
> 
>-asmlinkage const sys_call_ptr_t x32_sys_call_table[] = {
>+const sys_call_ptr_t x32_sys_call_table[] = {
> #include <asm/syscalls_x32.h>
> };
>diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
>index f44e2f9ab65d..f301919b9187 100644
>--- a/arch/x86/include/asm/syscall.h
>+++ b/arch/x86/include/asm/syscall.h
>@@ -16,20 +16,6 @@
> #include <asm/thread_info.h>	/* for TS_COMPAT */
> #include <asm/unistd.h>
> 
>-typedef long (*sys_call_ptr_t)(const struct pt_regs *);
>-extern const sys_call_ptr_t sys_call_table[];
>-
>-#if defined(CONFIG_X86_32)
>-#define ia32_sys_call_table sys_call_table
>-#else
>-/*
>- * These may not exist, but still put the prototypes in so we
>- * can use IS_ENABLED().
>- */
>-extern const sys_call_ptr_t ia32_sys_call_table[];
>-extern const sys_call_ptr_t x32_sys_call_table[];
>-#endif
>-
> /*
>  * Only the low 32 bits of orig_ax are meaningful, so we return int.
>  * This importantly ignores the high bits on 64-bit, so comparisons

__visible is for LTO, no?