bpf: fix pseudo calls for BPF programs loaded from ELF
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Commit Message
clang 6.0 and onwards, for the external function call generates
BPF_PSEUDO_CALL instruction:
call pseudo +-off -> call another bpf function.
More details about that change: https://lwn.net/Articles/741773/
DPDK BPF implementation right now doesn't support multiple BPF
functions per module.
To overcome that problem, and preserve existing functionality
(ability to call allowed by user external functions),
bpf_elf_load() clears EBPF_PSEUDO_CALL value.
For details how to reproduce the issue:
https://bugs.dpdk.org/show_bug.cgi?id=259
Fixes: 5dba93ae5f2d ("bpf: add ability to load eBPF program from ELF object file")
Cc: stable@dpdk.org
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
---
lib/librte_bpf/bpf_def.h | 8 ++++++++
lib/librte_bpf/bpf_load_elf.c | 15 +++++++++++++--
lib/librte_bpf/rte_bpf.h | 3 +++
3 files changed, 24 insertions(+), 2 deletions(-)
Comments
17/05/2019 16:09, Konstantin Ananyev:
> clang 6.0 and onwards, for the external function call generates
> BPF_PSEUDO_CALL instruction:
> call pseudo +-off -> call another bpf function.
> More details about that change: https://lwn.net/Articles/741773/
> DPDK BPF implementation right now doesn't support multiple BPF
> functions per module.
> To overcome that problem, and preserve existing functionality
> (ability to call allowed by user external functions),
> bpf_elf_load() clears EBPF_PSEUDO_CALL value.
> For details how to reproduce the issue:
> https://bugs.dpdk.org/show_bug.cgi?id=259
>
> Fixes: 5dba93ae5f2d ("bpf: add ability to load eBPF program from ELF object file")
> Cc: stable@dpdk.org
>
> Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Applied, thanks
@@ -120,6 +120,14 @@ enum {
EBPF_REG_NUM,
};
+/*
+ * When EBPF_CALL instruction has src_reg == EBPF_PSEUDO_CALL,
+ * it should be treated as pseudo-call instruction, where
+ * imm value contains pc-relative offset to another EBPF function.
+ * Right now DPDK EBPF library doesn't support it.
+ */
+#define EBPF_PSEUDO_CALL EBPF_REG_1
+
/*
* eBPF instruction format
*/
@@ -77,10 +77,21 @@ resolve_xsym(const char *sn, size_t ofs, struct ebpf_insn *ins, size_t ins_sz,
return -ENOENT;
/* for function we just need an index in our xsym table */
- if (type == RTE_BPF_XTYPE_FUNC)
+ if (type == RTE_BPF_XTYPE_FUNC) {
+
+ /* we don't support multiple functions per BPF module,
+ * so treat EBPF_PSEUDO_CALL to extrernal function
+ * as an ordinary EBPF_CALL.
+ */
+ if (ins[idx].src_reg == EBPF_PSEUDO_CALL) {
+ RTE_BPF_LOG(INFO, "%s(%u): "
+ "EBPF_PSEUDO_CALL to external function: %s\n",
+ __func__, idx, sn);
+ ins[idx].src_reg = EBPF_REG_0;
+ }
ins[idx].imm = fidx;
/* for variable we need to store its absolute address */
- else {
+ } else {
ins[idx].imm = (uintptr_t)prm->xsym[fidx].var.val;
ins[idx + 1].imm =
(uint64_t)(uintptr_t)prm->xsym[fidx].var.val >> 32;
@@ -134,6 +134,9 @@ rte_bpf_load(const struct rte_bpf_prm *prm);
/**
* Create a new eBPF execution context and load BPF code from given ELF
* file into it.
+ * Note that if the function will encounter EBPF_PSEUDO_CALL instruction
+ * that references external symbol, it will treat is as standard BPF_CALL
+ * to the external helper function.
*
* @param prm
* Parameters used to create and initialise the BPF execution context.