tree faeeec9791349c445e8b77856eaf09bb8b3da16f
parent 7005757fd573f03b88fc9d05a28cf3d91aa1d4f3
author Andrii Nakryiko <andriin@fb.com> 1552495981 -0700
committer Arnaldo Carvalho de Melo <acme@redhat.com> 1553885737 -0300

loaders: Strip away volatile/const/restrict when fixing bitfields

btf_loader and ctf_loader didn't remove const/volatile/restrict, so
bitfields using modifiers were not adjusted properly.

This patch abstracts logic of stripping aways typedefs and access
modifiers into tag__strip_typedefs_and_modifiers, which handles any
interleaving of typedefs and modifiers. dwarf_loader was adapter to
reuse this function as well, instead of custom goto loop.

REPRO:

  $ cat vc_map.c
  typedef unsigned int u32;
  typedef volatile u32 vu32;
  typedef vu32 vu32_t;

  typedef struct vc_map {
          volatile unsigned int tx: 1;
          vu32_t rx: 1;
          void *x1, *x2;
  } vc_map;

  int main() {
          struct vc_map s;
          return 0;
  }

BEFORE:

  $ ~/pahole/build/pahole -F btf vc_map
  struct vc_map {
          volatile unsigned int      tx:1;                 /*     0: 0  4 */
          vu32_t                     rx:1;                 /*     0: 0  4 */

          /* XXX 30 bits hole, try to pack */
          /* XXX 4 bytes hole, try to pack */

          void *                     x1;                   /*     8     8 */
          void *                     x2;                   /*    16     8 */

          /* size: 24, cachelines: 1, members: 4 */
          /* sum members: 20, holes: 1, sum holes: 4 */
          /* bit holes: 1, sum bit holes: 30 bits */
          /* last cacheline: 24 bytes */
  };

AFTER:

  $ ~/pahole/build/pahole -F btf vc_map
  struct vc_map {
          volatile unsigned int      tx:1;                 /*     0:31  4 */
          vu32_t                     rx:1;                 /*     0:30  4 */

          /* XXX 30 bits hole, try to pack */
          /* XXX 4 bytes hole, try to pack */

          void *                     x1;                   /*     8     8 */
          void *                     x2;                   /*    16     8 */

          /* size: 24, cachelines: 1, members: 4 */
          /* sum members: 20, holes: 1, sum holes: 4 */
          /* bit holes: 1, sum bit holes: 30 bits */
          /* last cacheline: 24 bytes */
  };

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>