On 6/19/23 4:49 AM, menglong8.dong@xxxxxxxxx wrote:
From: Menglong Dong <imagedong@xxxxxxxxxxx>
For now, the BPF program of type BPF_PROG_TYPE_TRACING can only be used
on the kernel functions whose arguments count less than 6. This is not
less than or equal to 6, if not considering '> 8 bytes'
struct arguments.
friendly at all, as too many functions have arguments count more than 6.
According to the current kernel version, below is a statistics of the
function arguments count:
argument count | function count
7 | 704
8 | 270
9 | 84
10 | 47
11 | 47
12 | 27
13 | 22
14 | 5
15 | 0
16 | 1
Therefore, let's enhance it by increasing the function arguments count
allowed in arch_prepare_bpf_trampoline(), for now, only x86_64.
In the 1st patch, we save/restore regs with BPF_DW size to make the code
in save_regs()/restore_regs() simpler.
In the 2nd patch, we make arch_prepare_bpf_trampoline() support to copy
function arguments in stack for x86 arch. Therefore, the maximum
arguments can be up to MAX_BPF_FUNC_ARGS for FENTRY and FEXIT.
for FENTRY, FEXIT and MODIFY_RETURN.
Meanwhile,
we clean the potentian garbage value when we copy the arguments on-stack.
potentian -> potential
And the 3rd patches are for the testcases of the this series.
the 3rd patch is ...
Changes since v5:
- adjust the commit log of the 1st patch, avoiding confusing people that
bugs exist in current code
- introduce get_nr_regs() to get the space that used to pass args on
stack correct in the 2nd patch
- add testcases to tracing_struct.c instead of fentry_test.c and
fexit_test.c
Changes since v4:
- consider the case of the struct in arguments can't be hold by regs
- add comment for some code
- add testcases for MODIFY_RETURN
- rebase to the latest
Changes since v3:
- try make the stack pointer 16-byte aligned. Not sure if I'm right :)
- introduce clean_garbage() to clean the grabage when argument count is 7
- use different data type in bpf_testmod_fentry_test{7,12}
- add testcase for grabage values in ctx
Changes since v2:
- keep MAX_BPF_FUNC_ARGS still
- clean garbage value in upper bytes in the 2nd patch
- move bpf_fentry_test{7,12} to bpf_testmod.c and rename them to
bpf_testmod_fentry_test{7,12} meanwhile in the 3rd patch
Changes since v1:
- change the maximun function arguments to 14 from 12
- add testcases (Jiri Olsa)
- instead EMIT4 with EMIT3_off32 for "lea" to prevent overflow
Menglong Dong (3):
bpf, x86: save/restore regs with BPF_DW size
bpf, x86: allow function arguments up to 12 for TRACING
selftests/bpf: add testcase for TRACING with 6+ arguments
arch/x86/net/bpf_jit_comp.c | 249 +++++++++++++++---
net/bpf/test_run.c | 23 +-
.../selftests/bpf/bpf_testmod/bpf_testmod.c | 49 +++-
.../selftests/bpf/prog_tests/fentry_fexit.c | 4 +-
.../selftests/bpf/prog_tests/fentry_test.c | 2 +
.../selftests/bpf/prog_tests/fexit_test.c | 2 +
.../selftests/bpf/prog_tests/modify_return.c | 20 +-
.../selftests/bpf/prog_tests/tracing_struct.c | 19 ++
.../testing/selftests/bpf/progs/fentry_test.c | 32 +++
.../testing/selftests/bpf/progs/fexit_test.c | 33 +++
.../selftests/bpf/progs/modify_return.c | 40 +++
.../selftests/bpf/progs/tracing_struct.c | 48 ++++
12 files changed, 471 insertions(+), 50 deletions(-)
