On 6/7/21 11:18 AM, Jiri Olsa wrote:
On Sun, Jun 06, 2021 at 08:56:47PM -0700, Yonghong Song wrote:
On 6/5/21 4:10 AM, Jiri Olsa wrote:
Adding support to load tracing program with new BPF_F_MULTI_FUNC flag,
that allows the program to be loaded without specific function to be
attached to.
The verifier assumes the program is using all (6) available arguments
Is this a verifier failure or it is due to the check in the
beginning of function arch_prepare_bpf_trampoline()?
/* x86-64 supports up to 6 arguments. 7+ can be added in the future
*/
if (nr_args > 6)
return -ENOTSUPP;
yes, that's the limit.. it allows the traced program to
touch 6 arguments, because it's the maximum for JIT
If it is indeed due to arch_prepare_bpf_trampoline() maybe we
can improve it instead of specially processing the first argument
"ip" in quite some places?
do you mean to teach JIT to process more than 6 arguments?
Yes. Not sure how hard it is. If it is doable with reasonable
complexity, I think it will be worth it as it will benefit this
case to avoid special tweaks of the first argument, but also
benefit other cases e.g., attaching to a kernel function with
7 or more arguments.
as unsigned long values. We can't add extra ip argument at this time,
because JIT on x86 would fail to process this function. Instead we
allow to access extra first 'ip' argument in btf_ctx_access.
Such program will be allowed to be attached to multiple functions
in following patches.
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 7 +++++++
kernel/bpf/btf.c | 5 +++++
kernel/bpf/syscall.c | 35 +++++++++++++++++++++++++++++-----
kernel/bpf/verifier.c | 3 ++-
tools/include/uapi/linux/bpf.h | 7 +++++++
6 files changed, 52 insertions(+), 6 deletions(-)
[...]
