linux-kernel - [PATCH 8/8] x86/asm/entry/64: Reduce padding in execve stubs

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Date:	Tue,  7 Apr 2015 22:43:44 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 8/8] x86/asm/entry/64: Reduce padding in execve stubs

execve stubs are 7 bytes only. Padding them to 16 bytes is a waste.

   text	   data	    bss	    dec	    hex	filename
  12594	      0	      0	  12594	   3132	entry_64.o.before
  12530	      0	      0	  12530	   30f2	entry_64.o

Run-tested.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Borislav Petkov <bp@...en8.de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Alexei Starovoitov <ast@...mgrid.com>
CC: Will Drewry <wad@...omium.org>
CC: Kees Cook <keescook@...omium.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/entry_64.S | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 05224d4..2aa3eca 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -434,8 +434,12 @@ return_from_execve:
 	jmp	int_ret_from_sys_call
 	CFI_ENDPROC
 END(stub_execve)
-
-ENTRY(stub_execveat)
+/*
+ * Remaining execve stubs are only 7 bytes long.
+ * ENTRY() often aligns to 16 bytes, which in this case has no benefits.
+ */
+	.align	8
+GLOBAL(stub_execveat)
 	CFI_STARTPROC
 	DEFAULT_FRAME 0, 8
 	call	sys_execveat
@@ -444,14 +448,16 @@ ENTRY(stub_execveat)
 END(stub_execveat)
 
 #ifdef CONFIG_X86_X32_ABI
-ENTRY(stub_x32_execve)
+	.align	8
+GLOBAL(stub_x32_execve)
 	CFI_STARTPROC
 	DEFAULT_FRAME 0, 8
 	call	compat_sys_execve
 	jmp	return_from_execve
 	CFI_ENDPROC
 END(stub_x32_execve)
-ENTRY(stub_x32_execveat)
+	.align	8
+GLOBAL(stub_x32_execveat)
 	CFI_STARTPROC
 	DEFAULT_FRAME 0, 8
 	call	compat_sys_execveat
@@ -461,13 +467,15 @@ END(stub_x32_execveat)
 #endif
 
 #ifdef CONFIG_IA32_EMULATION
-ENTRY(stub32_execve)
+	.align	8
+GLOBAL(stub32_execve)
 	CFI_STARTPROC
 	call	compat_sys_execve
 	jmp	return_from_execve
 	CFI_ENDPROC
 END(stub32_execve)
-ENTRY(stub32_execveat)
+	.align	8
+GLOBAL(stub32_execveat)
 	CFI_STARTPROC
 	call	compat_sys_execveat
 	jmp	return_from_execve
-- 
1.8.1.4

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