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

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