Commit a4046c06 authored Mar 13, 2019 by Pi-Hsun Shih Committed by Linus Torvalds Mar 14, 2019

include/linux/swap.h: use offsetof() instead of custom __swapoffset macro

Use offsetof() to calculate offset of a field to take advantage of
compiler built-in version when possible, and avoid UBSAN warning when
compiling with Clang:

  UBSAN: Undefined behaviour in mm/swapfile.c:3010:38
  member access within null pointer of type 'union swap_header'
  CPU: 6 PID: 1833 Comm: swapon Tainted: G S                4.19.23 #43
  Call trace:
   dump_backtrace+0x0/0x194
   show_stack+0x20/0x2c
   __dump_stack+0x20/0x28
   dump_stack+0x70/0x94
   ubsan_epilogue+0x14/0x44
   ubsan_type_mismatch_common+0xf4/0xfc
   __ubsan_handle_type_mismatch_v1+0x34/0x54
   __se_sys_swapon+0x654/0x1084
   __arm64_sys_swapon+0x1c/0x24
   el0_svc_common+0xa8/0x150
   el0_svc_compat_handler+0x2c/0x38
   el0_svc_compat+0x8/0x18

Link: http://lkml.kernel.org/r/20190312081902.223764-1-pihsun@chromium.org


Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 17415606

include/linux/swap.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -157,9 +157,9 @@ struct swap_extent {
		/*
		* Max bad pages in the new format..
		*/
		#define __swapoffset(x) ((unsigned long)&((union swap_header *)0)->x)
		#define MAX_SWAP_BADPAGES \
		((__swapoffset(magic.magic) - __swapoffset(info.badpages)) / sizeof(int))
		((offsetof(union swap_header, magic.magic) - \
		offsetof(union swap_header, info.badpages)) / sizeof(int))

		enum {
		SWP_USED = (1 << 0), /* is slot in swap_info[] used? */

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