Re: [PATCH 0/3] syscalls: clean up stub naming convention

From: Dominik Brodowski
Date: Sun Apr 08 2018 - 16:11:05 EST

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On Sun, Apr 08, 2018 at 11:15:36AM +0200, Dominik Brodowski wrote:
> On a somewhat related note: I'll try to prepare a patch this evening which
> lets us build just the __ia32_sys and __x32_compat_sys stubs we actually
> need. We have that information already in entry/syscalls/syscall_{32,64}.tbl,
> it just needs to be extracted into another header file (in the form of
> #define NEED_IA32_sys_xyzzz 1
> ) and then tested within the stubs. After some randconfig testing, this
> might be worthwile to add on top of the patches already in tip-asm and the
> three renaming patches currently under discussion.

So this got a bit more complicated than I though, for a -5k text size
decrease. I have my doubts whether the increased code complexity is really
worth that minor size decrease. I'll send another patch shortly, though,
which fixes up the naming of a few macros in <asm/syscall_wrapper.h>.

--------------------------------------------------------------------------
From: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Date: Sun, 8 Apr 2018 21:38:54 +0200
Subject: [PATCH] syscalls/x86: only build stubs which are actually needed

A new script arch/x86/entry/syscalls/syscallstubs.sh generates
defines in <asm/syscall_stubs.h>

for all __ia32_sys_ stubs which are actually needed for
IA32_EMULATION,

and

for all __x32_compat_sys_ stubs which are actually needed
for X32.

By omitting to build the remaining stubs (which are defined as
__SYSCALL_STUBx_UNUSED), there is a measurable decrease in kernel
size (-5k):

text data bss dec hex filename
12892057 7094202 13570252 33556511 200081f vmlinux-orig
12886397 7087514 13570252 33544163 1ffd7e3 vmlinux

Further size cuttings could be achieved by not building stubs for
syscalls and compat_syscalls which are not referenced in the syscall
tables, such as (at least)

sys_gethostname
sys_sync_file_range2
sys_send
sys_recv
compat_sys_mbind
compat_sys_set_mempolicy
compat_sys_migrate_pages
compat_sys_sendtimedop
compat_sys_msgrcv
compat_sys_semctl
compat_sys_send
compat_sys_recv

Not-yet-signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>

diff --git a/arch/x86/entry/syscalls/Makefile b/arch/x86/entry/syscalls/Makefile
index 6fb9b57ed5ba..036199136513 100644
--- a/arch/x86/entry/syscalls/Makefile
+++ b/arch/x86/entry/syscalls/Makefile
@@ -11,6 +11,7 @@ syscall64 := $(srctree)/$(src)/syscall_64.tbl

syshdr := $(srctree)/$(src)/syscallhdr.sh
systbl := $(srctree)/$(src)/syscalltbl.sh
+sysstubs := $(srctree)/$(src)/syscallstubs.sh

quiet_cmd_syshdr = SYSHDR $@
cmd_syshdr = $(CONFIG_SHELL) '$(syshdr)' '$<' '$@' \
@@ -20,6 +21,11 @@ quiet_cmd_syshdr = SYSHDR $@
quiet_cmd_systbl = SYSTBL $@
cmd_systbl = $(CONFIG_SHELL) '$(systbl)' $< $@

+quiet_cmd_sysstubs = SYSSTUBS $@
+ cmd_sysstubs = $(CONFIG_SHELL) '$(sysstubs)' \
+ '$(syscall32)' '$(syscall64)' \
+ $@
+
quiet_cmd_hypercalls = HYPERCALLS $@
cmd_hypercalls = $(CONFIG_SHELL) '$<' $@ $(filter-out $<,$^)

@@ -51,6 +57,9 @@ $(out)/syscalls_32.h: $(syscall32) $(systbl)
$(out)/syscalls_64.h: $(syscall64) $(systbl)
$(call if_changed,systbl)

+$(out)/syscall_stubs.h: $(syscall32) $(syscall64) $(sysstubs)
+ $(call if_changed,sysstubs)
+
$(out)/xen-hypercalls.h: $(srctree)/scripts/xen-hypercalls.sh
$(call if_changed,hypercalls)

@@ -60,6 +69,7 @@ uapisyshdr-y += unistd_32.h unistd_64.h unistd_x32.h
syshdr-y += syscalls_32.h
syshdr-$(CONFIG_X86_64) += unistd_32_ia32.h unistd_64_x32.h
syshdr-$(CONFIG_X86_64) += syscalls_64.h
+syshdr-$(CONFIG_X86_64) += syscall_stubs.h
syshdr-$(CONFIG_XEN) += xen-hypercalls.h

targets += $(uapisyshdr-y) $(syshdr-y)
diff --git a/arch/x86/entry/syscalls/syscallstubs.sh b/arch/x86/entry/syscalls/syscallstubs.sh
new file mode 100644
index 000000000000..4db64d4db75a
--- /dev/null
+++ b/arch/x86/entry/syscalls/syscallstubs.sh
@@ -0,0 +1,110 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+in32="$1"
+in64="$2"
+out="$3"
+
+emit_stub() {
+ entry="$1"
+ if [ "${entry}" != "${entry#__ia32_sys_}" ]; then
+ # We need a stub named __ia32_sys which is common to 64-bit
+ # except for a different pt_regs layout.
+ stubname=${entry#__ia32_sys_}
+ echo "#define __IA32_SYS_STUBx_${stubname} __IA32_SYS_STUBx"
+ echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
+ elif [ "$entry" != "${entry#__x32_compat_sys}" ]; then
+ # We need a stub named __x32_compat_sys_ which decodes a
+ # 64-bit pt_regs and then calls the real syscall function
+ stubname="${entry%%/*}" # handle qualifier
+ stubname=${stubname#__x32_compat_sys_} # handle prefix
+ echo "#define __X32_COMPAT_SYS_STUBx_${stubname} __X32_COMPAT_SYS_STUBx"
+ echo "#define ASM_X86_HAS__x32_compat_sys_${stubname} 1"
+ elif [ "$entry" != "${entry#__ia32_compat_sys_x86}" ]; then
+ # The compat entry starts with __ia32_compat_sys_x86, so it
+ # is a specific x86 compat syscall; no need for __ia32_sys_*()
+ stubname=${entry#__ia32_compat_sys_x86_}
+ echo "#define __IA32_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
+ echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
+ elif [ "$entry" != "${entry#__ia32_compat_sys_}" ]; then
+ # The compat entry starts with __ia32_compat_sys, so it is
+ # is a generic x86 compat syscall; no need for __ia32_sys_*()
+ stubname=${entry#__ia32_compat_sys_}
+ echo "#define __IA32_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
+ echo "#define ASM_X86_HAS__ia32_sys_${stubname} 1"
+ fi;
+}
+
+# First, we need to check which stubs we *need*. While at it, we can determine
+# quite many ia32 stubs we do *not* need as the syscall is handled by a compat
+# syscall
+grep '^[0-9]' "$in32" | sort -n | (
+ while read nr abi name entry compat; do
+ abi=`echo "$abi" | tr '[a-z]' '[A-Z]'`
+ if [ "$abi" = "I386" -a -n "$compat" ]; then
+ emit_stub "$compat"
+ fi
+ done
+) > "$out"
+
+grep '^[0-9]' "$in64" | sort -n | (
+ while read nr abi name entry compat; do
+ abi=`echo "$abi" | tr '[a-z]' '[A-Z]'`
+ if [ "$abi" = "X32" -a -n "$entry" ]; then
+ emit_stub "$entry"
+ fi
+ done
+) >> "$out"
+
+# Then, we need to determine all (remaining) stubs we *do not* need.
+grep '^[0-9]' "$in64" | sort -n | (
+ while read nr abi name entry compat; do
+ abi=`echo "$abi" | tr '[a-z]' '[A-Z]'`
+ if [ "$abi" = "COMMON" -o "$abi" = "64" ]; then
+ if [ -n "$entry" -a "$entry" != "${entry#__x64_sys_}" ]; then
+ # what's the actual stubname?
+ stubname="${entry%%/*}" # handle qualifier
+ stubname="${stubname#__x64_sys_}" # handle prefix
+
+ # syscalls only referenced for 64-bit do not need a stub for
+ # IA32_EMULATION
+ echo "#ifndef ASM_X86_HAS__ia32_sys_${stubname}"
+ echo "#define __IA32_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
+ echo "#endif"
+
+ # A number of compat syscalls are built in even though they are
+ # completely unused -- e.g. mbind set_mempolicy migrate_pages
+ # sendtimedop msgrcv semctl. We probably define more compat
+ # syscalls than exist, but better be safe than sorry...
+ echo "#ifndef ASM_X86_HAS__x32_compat_sys_${stubname}"
+ echo "#define __X32_COMPAT_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
+ echo "#endif"
+ fi
+ fi
+ done
+) >> "$out"
+
+grep '^[0-9]' "$in32" | sort -n | (
+ while read nr abi name entry compat; do
+ abi=`echo "$abi" | tr '[a-z]' '[A-Z]'`
+ if [ "$abi" = "I386" -a -n "$compat" ]; then
+ if [ "$compat" != "${compat#__ia32_compat_sys}" ]; then
+ stubname="${compat#__ia32_compat_sys_}"
+ # If a compat syscall is not needed for x32 (see above),
+ # we need to assert that the stub is defined as unused
+ echo "#ifndef ASM_X86_HAS__x32_compat_sys_${stubname}"
+ echo "#define __X32_COMPAT_SYS_STUBx_${stubname} __SYSCALL_STUBx_UNUSED"
+ echo "#endif"
+ fi
+ fi
+ done
+) >> "$out"
+
+# FIXME: These syscalls get build even though they are completely unused on x86
+( for unused_syscall in gethostname sync_file_range2 send recv; do
+ echo "#define __IA32_SYS_STUBx_${unused_syscall} __SYSCALL_STUBx_UNUSED"
+done ) >> "$out"
+( for unused_compat_syscall in send recv; do
+ echo "#define __X32_COMPAT_SYS_STUBx_${unused_compat_syscall} __SYSCALL_STUBx_UNUSED"
+done ) >> "$out"
+
diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
index de690c2d2e33..3aeb3a794da4 100644
--- a/arch/x86/include/asm/Kbuild
+++ b/arch/x86/include/asm/Kbuild
@@ -5,6 +5,7 @@ generated-y += syscalls_64.h
generated-y += unistd_32_ia32.h
generated-y += unistd_64_x32.h
generated-y += xen-hypercalls.h
+generated-y += syscall_stubs.h

generic-y += dma-contiguous.h
generic-y += early_ioremap.h
diff --git a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
index bad0295739bf..0b847f422bf6 100644
--- a/arch/x86/include/asm/syscall_wrapper.h
+++ b/arch/x86/include/asm/syscall_wrapper.h
@@ -4,7 +4,10 @@
*/

#ifndef _ASM_X86_SYSCALL_WRAPPER_H
-#define _ASM_X86_SYSCALL_WRAPPER_H
+#define _ASM_X86_SYSCALL_WRAPPER_H 1
+
+#define __SYSCALL_STUBx_UNUSED(x, name, ...)
+#include <asm/syscall_stubs.h>

/* Mapping of registers to parameters for syscalls on x86-64 and x32 */
#define SC_X86_64_REGS_TO_ARGS(x, ...) \
@@ -28,15 +31,15 @@
* kernel/sys_ni.c and SYS_NI in kernel/time/posix-stubs.c to cover this
* case as well.
*/
-#define COMPAT_SC_IA32_STUBx(x, name, ...) \
+#define __IA32_COMPAT_SYS_STUBx(x, name, ...) \
asmlinkage long __ia32_compat_sys##name(const struct pt_regs *regs);\
ALLOW_ERROR_INJECTION(__ia32_compat_sys##name, ERRNO); \
asmlinkage long __ia32_compat_sys##name(const struct pt_regs *regs)\
{ \
return __do_compat_sys##name(SC_IA32_REGS_TO_ARGS(x,__VA_ARGS__));\
- } \
+ }

-#define SC_IA32_WRAPPERx(x, name, ...) \
+#define __IA32_SYS_STUBx(x, name, ...) \
asmlinkage long __ia32_sys##name(const struct pt_regs *regs); \
ALLOW_ERROR_INJECTION(__ia32_sys##name, ERRNO); \
asmlinkage long __ia32_sys##name(const struct pt_regs *regs) \
@@ -64,8 +67,8 @@
SYSCALL_ALIAS(__ia32_sys_##name, sys_ni_posix_timers)

#else /* CONFIG_IA32_EMULATION */
-#define COMPAT_SC_IA32_STUBx(x, name, ...)
-#define SC_IA32_WRAPPERx(x, fullname, name, ...)
+#define __IA32_COMPAT_SYS_STUBx(x, name, ...)
+#define __IA32_SYS_STUBx(x, name, ...)
#endif /* CONFIG_IA32_EMULATION */

@@ -75,7 +78,7 @@
* of the x86-64-style parameter ordering of x32 syscalls. The syscalls common
* with x86_64 obviously do not need such care.
*/
-#define COMPAT_SC_X32_STUBx(x, name, ...) \
+#define __X32_COMPAT_SYS_STUBx(x, name, ...) \
asmlinkage long __x32_compat_sys##name(const struct pt_regs *regs);\
ALLOW_ERROR_INJECTION(__x32_compat_sys##name, ERRNO); \
asmlinkage long __x32_compat_sys##name(const struct pt_regs *regs)\
@@ -84,7 +87,7 @@
} \

#else /* CONFIG_X86_X32 */
-#define COMPAT_SC_X32_STUBx(x, name, ...)
+#define __X32_COMPAT_SYS_STUBx(x, name, ...)
#endif /* CONFIG_X86_X32 */

@@ -97,8 +100,8 @@
#define COMPAT_SYSCALL_DEFINEx(x, name, ...) \
static long __do_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
static inline long __in_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
- COMPAT_SC_IA32_STUBx(x, name, __VA_ARGS__) \
- COMPAT_SC_X32_STUBx(x, name, __VA_ARGS__) \
+ __IA32_COMPAT_SYS_STUBx(x, name, __VA_ARGS__) \
+ __X32_COMPAT_SYS_STUBx##name(x, name, __VA_ARGS__) \
static long __do_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
{ \
return __in_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__));\
@@ -120,7 +123,6 @@

#endif /* CONFIG_COMPAT */

-
/*
* Instead of the generic __SYSCALL_DEFINEx() definition, this macro takes
* struct pt_regs *regs as the only argument of the syscall stub named
@@ -163,7 +165,7 @@
{ \
return __do_sys##name(SC_X86_64_REGS_TO_ARGS(x,__VA_ARGS__));\
} \
- SC_IA32_WRAPPERx(x, name, __VA_ARGS__) \
+ __IA32_SYS_STUBx##name(x, name, __VA_ARGS__) \
static long __do_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
{ \
long ret = __in_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__));\

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