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s390/bpf: Implement bpf_jit_supports_subprog_tailcalls()

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Allow mixing subprogs and tail calls by passing the current tail
call count to subprogs.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230129190501.1624747-6-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Ilya Leoshkevich 2023-01-29 20:04:58 +01:00 committed by Alexei Starovoitov
parent 528eb2cb87
commit dd691e847d
1 changed files with 27 additions and 10 deletions
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37
arch/s390/net/bpf_jit_comp.c
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@ -58,7 +58,6 @@ struct bpf_jit {
#define SEEN_MEM BIT(0) /* use mem[] for temporary storage */
#define SEEN_LITERAL BIT(1) /* code uses literals */
#define SEEN_FUNC BIT(2) /* calls C functions */
#define SEEN_TAIL_CALL BIT(3) /* code uses tail calls */
#define SEEN_STACK (SEEN_FUNC | SEEN_MEM)
/*
@ -549,20 +548,23 @@ static void bpf_jit_plt(void *plt, void *ret, void *target)
* Save registers and create stack frame if necessary.
* See stack frame layout description in "bpf_jit.h"!
*/
static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth)
static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp,
u32 stack_depth)
{
/* No-op for hotpatching */
/* brcl 0,prologue_plt */
EMIT6_PCREL_RILC(0xc0040000, 0, jit->prologue_plt);
jit->prologue_plt_ret = jit->prg;
if (jit->seen & SEEN_TAIL_CALL) {
if (fp->aux->func_idx == 0) {
/* Initialize the tail call counter in the main program. */
/* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */
_EMIT6(0xd703f000 | STK_OFF_TCCNT, 0xf000 | STK_OFF_TCCNT);
} else {
/*
* There are no tail calls. Insert nops in order to have
* tail_call_start at a predictable offset.
* Skip the tail call counter initialization in subprograms.
* Insert nops in order to have tail_call_start at a
* predictable offset.
*/
bpf_skip(jit, 6);
}
@ -1410,6 +1412,19 @@ 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 STK_OFF_TCCNT(4,%r15),N(%r15) */
_EMIT6(0xd203f000 | STK_OFF_TCCNT,
0xf000 | (STK_OFF_TCCNT + STK_OFF + stack_depth));
/* lgrl %w1,func */
EMIT6_PCREL_RILB(0xc4080000, REG_W1, _EMIT_CONST_U64(func));
/* %r1() */
@ -1426,10 +1441,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
* B1: pointer to ctx
* B2: pointer to bpf_array
* B3: index in bpf_array
*/
jit->seen |= SEEN_TAIL_CALL;
/*
*
* if (index >= array->map.max_entries)
* goto out;
*/
@ -1793,7 +1805,7 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp,
jit->prg = 0;
jit->excnt = 0;
bpf_jit_prologue(jit, stack_depth);
bpf_jit_prologue(jit, fp, stack_depth);
if (bpf_set_addr(jit, 0) < 0)
return -1;
for (i = 0; i < fp->len; i += insn_count) {
@ -2462,3 +2474,8 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
return ret;
}
bool bpf_jit_supports_subprog_tailcalls(void)
{
return true;
}