dwarves: Revamp bit/byte holes detection logic
This patch rewrites hole detection logic. Now many crazy combinations of
bitfields and normal fields are handled correctly.
This was tested on allyesconfig kernel and differences before/after were
always in favor of new algorithm.
With subsequent change in next patch, there are no more BRAIN FART
ALERTs for allyesconfig and DWARF and BTF outputs have no discrepanies.
Example:
$ cat test.c
struct s {
short : 4; /* this one is not emitted in DWARF/BTF */
short a : 4;
int x;
int : 10;
int y : 4;
short zz;
short zzz : 4;
long z;
short : 4;
};
int main() {
struct s s;
return 0;
}
$ gcc -g test.c -o test
$ ~/pahole/build/pahole -J test
$ ~/pahole/build/pahole -F dwarf test
struct s {
/* XXX 4 bits hole, try to pack */
short int a:4; /* 0: 8 2 */
/* XXX 8 bits hole, try to pack */
/* XXX 2 bytes hole, try to pack */
int x; /* 4 4 */
/* XXX 10 bits hole, try to pack */
int y:4; /* 8:18 4 */
/* Bitfield combined with next fields */
/* XXX 2 bits hole, try to pack */
short int zz; /* 10 2 */
short int zzz:4; /* 12:12 2 */
/* XXX 12 bits hole, try to pack */
/* XXX 2 bytes hole, try to pack */
long int z; /* 16 8 */
/* size: 32, cachelines: 1, members: 6 */
/* sum members (bits): 124, holes: 2, sum holes: 4 */
/* bit holes: 5, sum bit holes: 36 bits */
/* padding: 8 */
/* last cacheline: 32 bytes */
};
No discrepanies between BTF/DWARF:
$ ../btfdiff test
$
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Mark Wielaard <mark@klomp.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: dwarves@vger.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
1 file changed
