tracing: Print a signed histogram key as signed

A histogram sorts its rows by the key named in sort=, and for a key over a
signed event field it sorts them signed: create_tracing_map_fields() picks
the comparison function with

	else
		cmp_fn = tracing_map_cmp_num(field->size,
					     field->is_signed);

hist_trigger_print_key() does not look at is_signed at all. Every numeric
key is printed with %llu, so a sorted histogram over a signed field comes
out looking unsorted. syscalls/sys_exit_lseek carries "long ret", which
SYSCALL_FIELD() marks signed and which is negative on every error:

  # echo 'hist:keys=ret:sort=ret' > events/syscalls/sys_exit_lseek/trigger
  # echo 1 > events/syscalls/sys_exit_lseek/enable
  # (five lseek(2) calls returning -ESPIPE, -EINVAL, -EBADF, 0 and 100)
  # cat events/syscalls/sys_exit_lseek/hist

  { ret: 18446744073709551587 } hitcount:          1
  { ret: 18446744073709551594 } hitcount:          1
  { ret: 18446744073709551607 } hitcount:          1
  { ret:          0 } hitcount:          1
  { ret:        100 } hitcount:          1

The rows are in ascending order and the numbers are not, because the three
leading ones are -29, -22 and -9 rendered as their two's complement.

Take the rendering from the same place the sort order comes from: the event
field when the key has one, and the hist_field itself when it does not. The
same histogram then reads

  { ret:        -29 } hitcount:          1
  { ret:        -22 } hitcount:          1
  { ret:         -9 } hitcount:          1
  { ret:          0 } hitcount:          1
  { ret:        100 } hitcount:          1

A ".buckets" key stays unsigned here, and not because it is right.
hist_field_bucket() divides as unsigned, so the group holding S64_MAX also
holds S64_MIN, reported at

  https://lore.kernel.org/all/20260914054614.82A9B1F000FF@smtp.kernel.org/

Printing that group signed would name a range that does not contain
S64_MIN, so the grouping has to be fixed with it, in a patch of its own.

Link: https://patch.msgid.link/20260917045918.370993-1-donggeunyoo.kernel@gmail.com
Fixes: 7ef224d1d0e3 ("tracing: Add 'hist' event trigger command")
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

0 files changed, 0 insertions, 0 deletions