bpftool: Support setting alternative arch for JIT disasm with LLVM

For offloaded BPF programs, instead of failing to create the
LLVM disassembler without even looking for a triple at all, do run the
function that attempts to retrieve a valid architecture name for the
device.

It will still fail for the LLVM disassembler, because currently we have
no valid triple to return (NFP disassembly is not supported by LLVM).
But failing in that function is more logical than to assume in
jit_disasm.c that passing an "arch" name is simply not supported.

Suggested-by: Song Liu <song@kernel.org>
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/r/20221025150329.97371-8-quentin@isovalent.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/common.c

@@ -627,12 +627,11 @@ static int read_sysfs_netdev_hex_int(char *devname, const char *entry_name)
 }
 
 const char *
-ifindex_to_bfd_params(__u32 ifindex, __u64 ns_dev, __u64 ns_ino,
-		      const char **opt)
+ifindex_to_arch(__u32 ifindex, __u64 ns_dev, __u64 ns_ino, const char **opt)
 {
+	__maybe_unused int device_id;
 	char devname[IF_NAMESIZE];
 	int vendor_id;
-	int device_id;
 
 	if (!ifindex_to_name_ns(ifindex, ns_dev, ns_ino, devname)) {
 		p_err("Can't get net device name for ifindex %d: %s", ifindex,
@@ -647,6 +646,7 @@ ifindex_to_bfd_params(__u32 ifindex, __u64 ns_dev, __u64 ns_ino,
 	}
 
 	switch (vendor_id) {
+#ifdef HAVE_LIBBFD_SUPPORT
 	case 0x19ee:
 		device_id = read_sysfs_netdev_hex_int(devname, "device");
 		if (device_id != 0x4000 &&
@@ -655,8 +655,10 @@ ifindex_to_bfd_params(__u32 ifindex, __u64 ns_dev, __u64 ns_ino,
 			p_info("Unknown NFP device ID, assuming it is NFP-6xxx arch");
 		*opt = "ctx4";
 		return "NFP-6xxx";
+#endif /* HAVE_LIBBFD_SUPPORT */
+	/* No NFP support in LLVM, we have no valid triple to return. */
 	default:
-		p_err("Can't get bfd arch name for device vendor id 0x%04x",
+		p_err("Can't get arch name for device vendor id 0x%04x",
 		      vendor_id);
 		return NULL;
 	}

tools/bpf/bpftool/jit_disasm.c

@@ -84,12 +84,10 @@ init_context(disasm_ctx_t *ctx, const char *arch,
 {
 	char *triple;
 
-	if (arch) {
-		p_err("Architecture %s not supported", arch);
-		return -1;
-	}
-
-	triple = LLVMGetDefaultTargetTriple();
+	if (arch)
+		triple = LLVMNormalizeTargetTriple(arch);
+	else
+		triple = LLVMGetDefaultTargetTriple();
 	if (!triple) {
 		p_err("Failed to retrieve triple");
 		return -1;
@@ -128,8 +126,9 @@ disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc)
 
 int disasm_init(void)
 {
-	LLVMInitializeNativeTarget();
-	LLVMInitializeNativeDisassembler();
+	LLVMInitializeAllTargetInfos();
+	LLVMInitializeAllTargetMCs();
+	LLVMInitializeAllDisassemblers();
 	return 0;
 }
 #endif /* HAVE_LLVM_SUPPORT */

tools/bpf/bpftool/main.h

@@ -203,8 +203,7 @@ void print_hex_data_json(uint8_t *data, size_t len);
 unsigned int get_page_size(void);
 unsigned int get_possible_cpus(void);
 const char *
-ifindex_to_bfd_params(__u32 ifindex, __u64 ns_dev, __u64 ns_ino,
-		      const char **opt);
+ifindex_to_arch(__u32 ifindex, __u64 ns_dev, __u64 ns_ino, const char **opt);
 
 struct btf_dumper {
 	const struct btf *btf;

tools/bpf/bpftool/prog.c

@@ -764,10 +764,8 @@ prog_dump(struct bpf_prog_info *info, enum dump_mode mode,
 		const char *name = NULL;
 
 		if (info->ifindex) {
-			name = ifindex_to_bfd_params(info->ifindex,
-						     info->netns_dev,
-						     info->netns_ino,
-						     &disasm_opt);
+			name = ifindex_to_arch(info->ifindex, info->netns_dev,
+					       info->netns_ino, &disasm_opt);
 			if (!name)
 				goto exit_free;
 		}