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s390/bpf: Write back the tail call counter #9455

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s390/bpf: Write back the tail call counter #9455

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69433ca
s390/bpf: Write back the tail call counter for BPF_CALL
iii-i Aug 12, 2025
0931a02
s390/bpf: Write back the tail call counter for BPF_TRAMP_F_CALL_ORIG
iii-i Aug 12, 2025
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23 changes: 16 additions & 7 deletions arch/s390/net/bpf_jit_comp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1790,16 +1790,11 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,

REG_SET_SEEN(BPF_REG_5);
jit->seen |= SEEN_FUNC;

/*
* Copy the tail call counter to where the callee expects it.
*
* Note 1: The callee can increment the tail call counter, but
* we do not load it back, since the x86 JIT does not do this
* either.
*
* Note 2: We assume that the verifier does not let us call the
* main program, which clears the tail call counter on entry.
*/

/* mvc tail_call_cnt(4,%r15),frame_off+tail_call_cnt(%r15) */
_EMIT6(0xd203f000 | offsetof(struct prog_frame, tail_call_cnt),
0xf000 | (jit->frame_off +
Expand All @@ -1825,6 +1820,17 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
call_r1(jit);
/* lgr %b0,%r2: load return value into %b0 */
EMIT4(0xb9040000, BPF_REG_0, REG_2);

/*
* Copy the potentially updated tail call counter back.
*/

/* mvc frame_off+tail_call_cnt(%r15),tail_call_cnt(4,%r15) */
_EMIT6(0xd203f000 | (jit->frame_off +
offsetof(struct prog_frame,
tail_call_cnt)),
0xf000 | offsetof(struct prog_frame, tail_call_cnt));

break;
}
case BPF_JMP | BPF_TAIL_CALL: {
Expand Down Expand Up @@ -2822,6 +2828,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
/* stg %r2,retval_off(%r15) */
EMIT6_DISP_LH(0xe3000000, 0x0024, REG_2, REG_0, REG_15,
tjit->retval_off);
/* mvc tccnt_off(%r15),tail_call_cnt(4,%r15) */
_EMIT6(0xd203f000 | tjit->tccnt_off,
0xf000 | offsetof(struct prog_frame, tail_call_cnt));

im->ip_after_call = jit->prg_buf + jit->prg;

Expand Down
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