Darling: Linux Kernel Module build fails on Linux 5.4.0+

Created on 9 Jan 2020 · 5Comments · Source: darlinghq/darling

Problem

Found on 5.4.6, may be encountered earlier.

Some functions under the same name as ones in libkern were introduced, causing a name conflict.

  CC [M]  /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.o
In file included from /home/vmuser/darling/src/lkm/osfmk/mach/mach_types.h:112,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/clock.h:38,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/sched_prim.h:72,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:76:
/home/vmuser/darling/src/lkm/osfmk/mach/vm_param.h:275:18: error: ‘page_size’ redeclared as different kind of symbol
  275 | extern vm_size_t page_size;
      |                  ^~~~~~~~~
In file included from /home/vmuser/darling/src/lkm/osfmk/duct/duct.h:54,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:67:
./include/linux/mm.h:810:29: note: previous definition of ‘page_size’ was here
  810 | static inline unsigned long page_size(struct page *page)
      |                             ^~~~~~~~~
In file included from /home/vmuser/darling/src/lkm/osfmk/mach/mach_types.h:112,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/clock.h:38,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/sched_prim.h:72,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:76:
/home/vmuser/darling/src/lkm/osfmk/mach/vm_param.h:277:13: error: ‘page_shift’ redeclared as different kind of symbol
  277 | extern int  page_shift;
      |             ^~~~~~~~~~
In file included from /home/vmuser/darling/src/lkm/osfmk/duct/duct.h:54,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:67:
./include/linux/mm.h:816:28: note: previous definition of ‘page_shift’ was here
  816 | static inline unsigned int page_shift(struct page *page)
      |                            ^~~~~~~~~~
In file included from /home/vmuser/darling/src/lkm/osfmk/i386/user_ldt.h:72,
                 from /home/vmuser/darling/src/lkm/osfmk/i386/task.h:61,
                 from /home/vmuser/darling/src/lkm/osfmk/machine/task.h:32,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/task.h:108,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/thread.h:123,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/sched_prim.h:74,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:76:
/home/vmuser/darling/src/lkm/osfmk/i386/seg.h:213: warning: "SZ_64" redefined
  213 | #define SZ_64  0x2   /* 64-bit segment */
      | 
In file included from ./include/linux/mm.h:29,
                 from /home/vmuser/darling/src/lkm/osfmk/duct/duct.h:54,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:67:
./include/linux/sizes.h:16: note: this is the location of the previous definition
   16 | #define SZ_64    0x00000040
      | 
In file included from /home/vmuser/darling/src/lkm/osfmk/i386/user_ldt.h:72,
                 from /home/vmuser/darling/src/lkm/osfmk/i386/task.h:61,
                 from /home/vmuser/darling/src/lkm/osfmk/machine/task.h:32,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/task.h:108,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/thread.h:123,
                 from /home/vmuser/darling/src/lkm/osfmk/kern/sched_prim.h:74,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:76:
/home/vmuser/darling/src/lkm/osfmk/i386/seg.h:214: warning: "SZ_32" redefined
  214 | #define SZ_32  0x4   /* 32-bit segment */
      | 
In file included from ./include/linux/mm.h:29,
                 from /home/vmuser/darling/src/lkm/osfmk/duct/duct.h:54,
                 from /home/vmuser/darling/src/lkm/osfmk/ipc/ipc_entry.c:67:
./include/linux/sizes.h:15: note: this is the location of the previous definition
   15 | #define SZ_32    0x00000020
      |

We are defining functions under those names here:

https://github.com/darlinghq/darling-newlkm/blob/55f417505ce569bb513a50f9139f1ef87bf62e28/osfmk/mach/vm_param.h#L275-L277

The name conflicts in question are page_size and page_shift. They were added to the Linux headers in September.

https://github.com/torvalds/linux/blob/master/include/linux/mm.h#L794-L804

Solution

Our usages of the symbol may have to be renamed or aliased in some form. Or the Linux headers must be somehow avoided in the contexts where the XNU versions of these symbols are needed. Not necessarily straightforward.

Source