Commit 0e3727a8 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by H. Peter Anvin
Browse files

x86/vdso: Remove some redundant in-memory section headers 



.data doesn't need to be separate from .rodata: they're both readonly.

.altinstructions and .altinstr_replacement aren't needed by anything
except vdso2c; strip them from the final image.

While we're at it, rather than aligning the actual executable text,
just shove some unused-at-runtime data in between real data and
text.

My vdso image is still above 4k, but I'm disinclined to try to
trim it harder for 3.16.  For future trimming, I suspect that these
sections could be moved to later in the file and dropped from
the in-memory image:

.gnu.version and .gnu.version_d   (this may lose versions in gdb)
.eh_frame                         (should be harmless)
.eh_frame_hdr                     (I'm not really sure)
.hash                             (AFAIK nothing needs this section header)

Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/2e96d0c49016ea6d026a614ae645e93edd325961.1403129369.git.luto@amacapital.net


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent bfad381c

arch/x86/vdso/vdso-fakesections.c

+0 −3
Original line number Diff line number Diff line
@@ -16,9 +16,6 @@ const char fake_shstrtab[] __attribute__((section(".fake_shstrtab"))) = 
	".rodata\0"

	".fake_shstrtab\0"  /* Yay, self-referential code. */

	".note\0"

	".data\0"

	".altinstructions\0"

	".altinstr_replacement\0"

	".eh_frame_hdr\0"

	".eh_frame\0"

	".text";

arch/x86/vdso/vdso-layout.lds.S

+23 −20
Original line number Diff line number Diff line
@@ -14,7 +14,7 @@ 
# error unknown VDSO target

#endif



#define NUM_FAKE_SHDRS 16

#define NUM_FAKE_SHDRS 13



SECTIONS

{
@@ -28,15 +28,17 @@ SECTIONS 
	.gnu.version_d	: { *(.gnu.version_d) }

	.gnu.version_r	: { *(.gnu.version_r) }



	.note		: { *(.note.*) }		:text	:note



	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr

	.eh_frame	: { KEEP (*(.eh_frame)) }	:text



	.dynamic	: { *(.dynamic) }		:text	:dynamic



	.rodata		: {

		*(.rodata*)

		*(.data*)

		*(.sdata*)

		*(.got.plt) *(.got)

		*(.gnu.linkonce.d.*)

		*(.bss*)

		*(.dynbss*)

		*(.gnu.linkonce.b.*)



		/*

		 * Ideally this would live in a C file, but that won't
@@ -50,27 +52,28 @@ SECTIONS 


	.fake_shstrtab	: { *(.fake_shstrtab) }		:text



	.data		: {

		*(.data*)

		*(.sdata*)

		*(.got.plt) *(.got)

		*(.gnu.linkonce.d.*)

		*(.bss*)

		*(.dynbss*)

		*(.gnu.linkonce.b.*)

	}



	.altinstructions	: { *(.altinstructions) }

	.altinstr_replacement	: { *(.altinstr_replacement) }

	.note		: { *(.note.*) }		:text	:note



	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr

	.eh_frame	: { KEEP (*(.eh_frame)) }	:text





	/*

	 * Align the actual code well away from the non-instruction data.

	 * This is the best thing for the I-cache.

	 * Text is well-separated from actual data: there's plenty of

	 * stuff that isn't used at runtime in between.

	 */

	. = ALIGN(0x100);



	.text		: { *(.text*) }			:text	=0x90909090,



	/*

	 * At the end so that eu-elflint stays happy when vdso2c strips

	 * these.  A better implementation would avoid allocating space

	 * for these.

	 */

	.altinstructions	: { *(.altinstructions) }	:text

	.altinstr_replacement	: { *(.altinstr_replacement) }	:text



	/*

	 * The remainder of the vDSO consists of special pages that are

	 * shared between the kernel and userspace.  It needs to be at the

arch/x86/vdso/vdso2c.h

+3 −1
Original line number Diff line number Diff line
@@ -92,7 +92,9 @@ static void BITSFUNC(copy_section)(struct BITSFUNC(fake_sections) *out, 
{

	uint64_t flags = GET_LE(&in->sh_flags);



	bool copy = flags & SHF_ALLOC;

	bool copy = flags & SHF_ALLOC &&

		strcmp(name, ".altinstructions") &&

		strcmp(name, ".altinstr_replacement");



	if (!copy)

		return;

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