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bpf, x86: Store caller's ip in trampoline stack

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Storing caller's ip in trampoline's stack. Trampoline programs
can reach the IP in (ctx - 8) address, so there's no change in
program's arguments interface.

The IP address is takes from [fp + 8], which is return address
from the initial 'call fentry' call to trampoline.

This IP address will be returned via bpf_get_func_ip helper
helper, which is added in following patches.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210714094400.396467-2-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2021-07-14 11:43:53 +02:00 • committed by Alexei Starovoitov
parent 7628317192
commit 7e6f3cd89f
2 changed files with 24 additions and 0 deletions
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5
include/linux/bpf.h
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@ -579,6 +579,11 @@ struct btf_func_model {
*/
#define BPF_TRAMP_F_SKIP_FRAME BIT(2)
/* Store IP address of the caller on the trampoline stack,
* so it's available for trampoline's programs.
*/
#define BPF_TRAMP_F_IP_ARG BIT(3)
/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
* bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2
*/