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authorIlya Leoshkevich <iii@linux.ibm.com>2019-11-18 19:03:37 +0100
committerAlexei Starovoitov <ast@kernel.org>2019-11-18 19:51:16 -0800
commitc1aff5682da2977c26fc087cf6a28e31a430174b (patch)
tree11140c655c168fa2f1cdfce89b15276f16d58596
parente0491f64795bfc71ef6b13ba6b6fa6e176fa3c23 (diff)
downloadlinux-c1aff5682da2977c26fc087cf6a28e31a430174b.tar.bz2
s390/bpf: Load literal pool register using larl
Currently literal pool register is loaded using basr, which makes it point not to the beginning of the literal pool, but rather to the next instruction. In case JITed code is larger than 512k, this renders literal pool register absolutely useless due to long displacement range restrictions. The solution is to use larl to make literal pool register point to the very beginning of the literal pool. This makes it always possible to address 512k worth of literal pool entries using long displacement. However, for short programs, in which the entire literal pool is covered by basr-generated base, it is still beneficial to use basr, since it is 4 bytes shorter than larl. Detect situations when basr-generated base does not cover the entire literal pool, and in such cases use larl instead. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20191118180340.68373-4-iii@linux.ibm.com
-rw-r--r--arch/s390/net/bpf_jit_comp.c22
1 files changed, 19 insertions, 3 deletions
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index bb0215d290f4..964a09fd10f1 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -353,6 +353,15 @@ static bool can_use_rel(struct bpf_jit *jit, int off)
}
/*
+ * Return whether given displacement can be encoded using
+ * Long-Displacement Facility
+ */
+static bool is_valid_ldisp(int disp)
+{
+ return disp >= -524288 && disp <= 524287;
+}
+
+/*
* Fill whole space with illegal instructions
*/
static void jit_fill_hole(void *area, unsigned int size)
@@ -476,9 +485,16 @@ static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth)
save_restore_regs(jit, REGS_SAVE, stack_depth);
/* Setup literal pool */
if (is_first_pass(jit) || (jit->seen & SEEN_LITERAL)) {
- /* basr %r13,0 */
- EMIT2(0x0d00, REG_L, REG_0);
- jit->base_ip = jit->prg;
+ if (!is_first_pass(jit) &&
+ is_valid_ldisp(jit->size - (jit->prg + 2))) {
+ /* basr %l,0 */
+ EMIT2(0x0d00, REG_L, REG_0);
+ jit->base_ip = jit->prg;
+ } else {
+ /* larl %l,lit32_start */
+ EMIT6_PCREL_RILB(0xc0000000, REG_L, jit->lit32_start);
+ jit->base_ip = jit->lit32_start;
+ }
}
/* Setup stack and backchain */
if (is_first_pass(jit) || (jit->seen & SEEN_STACK)) {