arg_track_join() logs state transitions at CFG merge points. For
stack arg slots (r >= MAX_BPF_REG), it printed "r11:", "r12:", etc.,
which is misleading since r11 is a special register (BPF_REG_PARAMS)
not meaningful to the user.

Fix it to print "sa0:", "sa1:", etc., matching the per-instruction
transition log in arg_track_log() which already uses the "sa" prefix.

Update the existing stack_arg_pruning_type_mismatch selftest to expect
the corrected format.

Fixes: 2af4e792773f ("bpf: Extend liveness analysis to track stack argument slots")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260515225056.823086-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Commit 2af4e792773f ("bpf: Extend liveness analysis to track stack argument slots")
added stack arg supports. For selftest
  verifier_stack_arg/stack_arg: pruning with different stack arg types
the following are two arg JOIN messages:
  arg JOIN insn 9 -> 10 r1: fp0-8 + _ => fp0-8|fp0+0
  arg JOIN insn 9 -> 10 r11: fp0-8 + _ => fp0-8|fp0+0

Here the "r11:" label for stack arg slot 0 is misleading since r11
is a special register (BPF_REG_PARAMS). The next patch corrects
this to "sa0:", properly representing the 'stack arg slot 0'.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260515225051.822739-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add negative tests for the outgoing stack arg validation.
A static subprog with a 'long *' arg causes
btf_prepare_func_args() to fail after setting arg_cnt. The
validation ensures check_outgoing_stack_args() still runs.

Also update two existing tests (release_ref, stale_pkt_ptr) whose
expected error messages changed: invalidated stack arg slots are now
caught by check_outgoing_stack_args() at the call site instead of
at the callee's dereference.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260515225045.822104-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Now that arm64 supports stack arguments, enable the existing stack_arg,
stack_arg_kfunc and verifier_stack_arg tests for __TARGET_ARCH_arm64.

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260513045204.2403441-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Add inline-asm based verifier tests that exercise stack argument
validation logic directly.

Positive tests:
  - subprog call with 6 arg's
  - Two sequential calls to different subprogs (6-arg and 7-arg)
  - Share a r11 store for both branches

Negative tests — verifier rejection:
  - Read from uninitialized incoming stack arg slot
  - Gap in outgoing slots: only r11-16 written, r11-8 missing
  - Write at r11-80, exceeding max 7 stack args
  - Missing store on one branch with a shared store
  - First call has proper stack arguments and the second
    call intends to inherit stack arguments but not working
  - r11 load ordering issue

Negative tests — pointer/ref tracking:
  - Pruning type mismatch: one branch stores PTR_TO_STACK, the
    other stores a scalar, callee dereferences — must not prune
  - Release invalidation: bpf_sk_release invalidates a socket
    pointer stored in a stack arg slot
  - Packet pointer invalidation: bpf_skb_pull_data invalidates
    a packet pointer stored in a stack arg slot
  - Null propagation: PTR_TO_MAP_VALUE_OR_NULL stored in stack
    arg slot, null branch attempts dereference via callee

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260513045143.2399278-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>