On Wed, Jan 30, 2019 at 01:46:54PM +0100, Jiri Slaby wrote:
> Use the new SYM_DATA, SYM_DATA_START, and SYM_DATA_END in both 32 and 64
> bit heads. In the 64-bit version, define also
> SYM_DATA_START_PAGE_ALIGNED locally using the new SYM_START. It is used
> in the code instead of NEXT_PAGE() which was defined in this file and
> has been using the obsolete macro GLOBAL().
>
> Now, the data in the 64-bit object file look sane:
> Value Size Type Bind Vis Ndx Name
> 0000 4096 OBJECT GLOBAL DEFAULT 15 init_level4_pgt
> 1000 4096 OBJECT GLOBAL DEFAULT 15 level3_kernel_pgt
> 2000 2048 OBJECT GLOBAL DEFAULT 15 level2_kernel_pgt
^^^^
Except that this size is kinda misleading.
We end up using a whole page for this because of the alignment of the
next one but because we're not filing it up properly, the symbol has the
size of a half a page:
ffffffff8200f000 <level2_kernel_pgt>:
ffffffff8200f7f6: 00 00 add %al,(%rax)
ffffffff8200f7f8: e3 01 jrcxz ffffffff8200f7fb <level2_kernel_pgt+0x7fb>
ffffffff8200f7fa: e0 1f loopne ffffffff8200f81b <level2_kernel_pgt+0x81b>
...
ffffffff82010000 <level2_fixmap_pgt>:
That's a whole page with 2K padding.
You can do this in a prepatch:
---
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 5b7a3b430dea..93a9fd294962 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -448,6 +448,7 @@ SYM_DATA_START_PAGE_ALIGNED(level2_kernel_pgt)
*/
PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
KERNEL_IMAGE_SIZE/PMD_SIZE)
+ .fill 512 - KERNEL_IMAGE_SIZE/PMD_SIZE,8,0
SYM_DATA_END(level2_kernel_pgt)
SYM_DATA_START_PAGE_ALIGNED(level2_fixmap_pgt)
---
and then we get the proper symbol size:
69952: ffffffff8200f000 4096 OBJECT GLOBAL DEFAULT 11 level2_kernel_pgt
Thx.
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
