As I said in previous messages, I have become a huge fan of pahole. I've
been working with it rather closely and noticed some, well, oddities in
how pointer modifiers are printed and wanted to help by attempting to
provide a fix.
Assume that we have a C (named, say, modifier.c) with the contents:
struct S {
volatile int * volatile W;
const int * const X;
const int * volatile Y;
volatile int * const Z;
int ** const A;
int * const * B;
int * volatile * C;
const int * volatile * D;
};
struct S global_s;
int main() {
return 0;
}
If we compile it with
gcc -gbtf -g -O0 -o modifier modifier.c
... we can ask what gdb thinks about the types:
$ gdb modifier
(gdb) ptype global_s
type = struct S {
volatile int * volatile W;
const int * const X;
const int * volatile Y;
volatile int * const Z;
int ** const A;
int * const *B;
int * volatile *C;
const int * volatile *D;
}
With pahole (compiled from master), we get the following output:
$ ../build/pahole -F btf --compile modifier
struct S {
volatile volatile int * W; /* 0 8 */
const const int * X; /* 8 8 */
volatile const int * Y; /* 16 8 */
const volatile int * Z; /* 24 8 */
const int * * A; /* 32 8 */
int * const * B; /* 40 8 */
volatile int * * C; /* 48 8 */
volatile const int * * D; /* 56 8 */
/* size: 64, cachelines: 1, members: 8 */
};
$ ../build/pahole -F dwarf --compile modifier
struct S {
volatile volatile int * W; /* 0 8 */
const const int * X; /* 8 8 */
volatile const int * Y; /* 16 8 */
const volatile int * Z; /* 24 8 */
const int * * A; /* 32 8 */
int * const * B; /* 40 8 */
volatile int * * C; /* 48 8 */
volatile const int * * D; /* 56 8 */
/* size: 64, cachelines: 1, members: 8 */
};
This is not quite right. With the fix (attached) applied, we instead get
output that looks arguably correct:
$ ../build/pahole -F btf --compile modifier
struct S {
volatile int * volatile W; /* 0 8 */
const int * const X; /* 8 8 */
const int * volatile Y; /* 16 8 */
volatile int * const Z; /* 24 8 */
int * * const A; /* 32 8 */
int * const * B; /* 40 8 */
int * volatile * C; /* 48 8 */
const int * volatile * D; /* 56 8 */
/* size: 64, cachelines: 1, members: 8 */
};
$ ../build/pahole -F dwarf --compile modifierstruct S {
volatile int * volatile W; /* 0 8 */
const int * const X; /* 8 8 */
const int * volatile Y; /* 16 8 */
volatile int * const Z; /* 24 8 */
int * * const A; /* 32 8 */
int * const * B; /* 40 8 */
int * volatile * C; /* 48 8 */
const int * volatile * D; /* 56 8 */
/* size: 64, cachelines: 1, members: 8 */
};
I hope that this is helpful.
If the patch is useful but needs changes, please let me know! I would be
glad to make any changes to fit the codebase.
Thank you for all that you do to keep pahole going!
Will
Will Hawkins (1):
dwarves_fprintf: Handle pointer modifiers correctly
dwarves_fprintf.c | 57 ++++++++++++++---------------------------------
1 file changed, 17 insertions(+), 40 deletions(-)
--
2.45.2
