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bpf: Add get_func_[arg|ret|arg_cnt] helpers

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Adding following helpers for tracing programs:

Get n-th argument of the traced function:
  long bpf_get_func_arg(void *ctx, u32 n, u64 *value)

Get return value of the traced function:
  long bpf_get_func_ret(void *ctx, u64 *value)

Get arguments count of the traced function:
  long bpf_get_func_arg_cnt(void *ctx)

The trampoline now stores number of arguments on ctx-8
address, so it's easy to verify argument index and find
return value argument's position.

Moving function ip address on the trampoline stack behind
the number of functions arguments, so it's now stored on
ctx-16 address if it's needed.

All helpers above are inlined by verifier.

Also bit unrelated small change - using newly added function
bpf_prog_has_trampoline in check_get_func_ip.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211208193245.172141-5-jolsa@kernel.org
This commit is contained in:
Jiri Olsa
2021-12-08 20:32:44 +01:00
committed by Alexei Starovoitov
parent 5edf6a1983
commit f92c1e1836
7 changed files with 209 additions and 7 deletions
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28
tools/include/uapi/linux/bpf.h
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@@ -4993,6 +4993,31 @@ union bpf_attr {
* An integer less than, equal to, or greater than zero
* if the first **s1_sz** bytes of **s1** is found to be
* less than, to match, or be greater than **s2**.
*
* long bpf_get_func_arg(void *ctx, u32 n, u64 *value)
* Description
* Get **n**-th argument (zero based) of the traced function (for tracing programs)
* returned in **value**.
*
* Return
* 0 on success.
* **-EINVAL** if n >= arguments count of traced function.
*
* long bpf_get_func_ret(void *ctx, u64 *value)
* Description
* Get return value of the traced function (for tracing programs)
* in **value**.
*
* Return
* 0 on success.
* **-EOPNOTSUPP** for tracing programs other than BPF_TRACE_FEXIT or BPF_MODIFY_RETURN.
*
* long bpf_get_func_arg_cnt(void *ctx)
* Description
* Get number of arguments of the traced function (for tracing programs).
*
* Return
* The number of arguments of the traced function.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5178,6 +5203,9 @@ union bpf_attr {
FN(find_vma), \
FN(loop), \
FN(strncmp), \
FN(get_func_arg), \
FN(get_func_ret), \
FN(get_func_arg_cnt), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper