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From:   Alan Maguire <alan.maguire@oracle.com>
To:     ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org
Cc:     kafai@fb.com, songliubraving@fb.com, yhs@fb.com,
        john.fastabend@gmail.com, kpsingh@kernel.org, morbo@google.com,
        shuah@kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        Alan Maguire <alan.maguire@oracle.com>
Subject: [PATCH bpf-next 1/3] libbpf: avoid use of __int128 in typed dump display
Date:   Mon, 19 Jul 2021 22:41:27 +0100
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__int128 is not supported for some 32-bit platforms (arm and i386).
__int128 was used in carrying out computations on bitfields which
aid display, but the same calculations could be done with __u64
with the small effect of not supporting 128-bit bitfields.

With these changes, a big-endian issue with casting 128-bit integers
to 64-bit for enum bitfields is solved also, as we now use 64-bit
integers for bitfield calculations.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/btf_dump.c | 62 +++++++++++++++++++++++++++---------------------
 1 file changed, 35 insertions(+), 27 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index accf6fe..4a25512 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1552,28 +1552,15 @@ static int btf_dump_unsupported_data(struct btf_dump *d,
 	return -ENOTSUP;
 }
 
-static void btf_dump_int128(struct btf_dump *d,
-			    const struct btf_type *t,
-			    const void *data)
-{
-	__int128 num = *(__int128 *)data;
-
-	if ((num >> 64) == 0)
-		btf_dump_type_values(d, "0x%llx", (long long)num);
-	else
-		btf_dump_type_values(d, "0x%llx%016llx", (long long)num >> 32,
-				     (long long)num);
-}
-
-static unsigned __int128 btf_dump_bitfield_get_data(struct btf_dump *d,
-						    const struct btf_type *t,
-						    const void *data,
-						    __u8 bits_offset,
-						    __u8 bit_sz)
+static __u64 btf_dump_bitfield_get_data(struct btf_dump *d,
+					const struct btf_type *t,
+					const void *data,
+					__u8 bits_offset,
+					__u8 bit_sz)
 {
 	__u16 left_shift_bits, right_shift_bits;
 	__u8 nr_copy_bits, nr_copy_bytes;
-	unsigned __int128 num = 0, ret;
+	__u64 num = 0, ret;
 	const __u8 *bytes = data;
 	int i;
 
@@ -1591,8 +1578,8 @@ static unsigned __int128 btf_dump_bitfield_get_data(struct btf_dump *d,
 #else
 # error "Unrecognized __BYTE_ORDER__"
 #endif
-	left_shift_bits = 128 - nr_copy_bits;
-	right_shift_bits = 128 - bit_sz;
+	left_shift_bits = 64 - nr_copy_bits;
+	right_shift_bits = 64 - bit_sz;
 
 	ret = (num << left_shift_bits) >> right_shift_bits;
 
@@ -1605,7 +1592,7 @@ static int btf_dump_bitfield_check_zero(struct btf_dump *d,
 					__u8 bits_offset,
 					__u8 bit_sz)
 {
-	__int128 check_num;
+	__u64 check_num;
 
 	check_num = btf_dump_bitfield_get_data(d, t, data, bits_offset, bit_sz);
 	if (check_num == 0)
@@ -1619,10 +1606,11 @@ static int btf_dump_bitfield_data(struct btf_dump *d,
 				  __u8 bits_offset,
 				  __u8 bit_sz)
 {
-	unsigned __int128 print_num;
+	__u64 print_num;
 
 	print_num = btf_dump_bitfield_get_data(d, t, data, bits_offset, bit_sz);
-	btf_dump_int128(d, t, &print_num);
+
+	btf_dump_type_values(d, "0x%llx", (unsigned long long)print_num);
 
 	return 0;
 }
@@ -1681,9 +1669,29 @@ static int btf_dump_int_data(struct btf_dump *d,
 		return btf_dump_bitfield_data(d, t, data, 0, 0);
 
 	switch (sz) {
-	case 16:
-		btf_dump_int128(d, t, data);
+	case 16: {
+		const __u64 *ints = data;
+		__u64 lsi, msi;
+
+		/* avoid use of __int128 as some 32-bit platforms do not
+		 * support it.
+		 */
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+		lsi = ints[0];
+		msi = ints[1];
+#elif __BYTE_ORDER == __BIG_ENDIAN
+		lsi = ints[1];
+		msi = ints[0];
+#else
+# error "Unrecognized __BYTE_ORDER__"
+#endif
+		if (msi == 0)
+			btf_dump_type_values(d, "0x%llx", (unsigned long long)lsi);
+		else
+			btf_dump_type_values(d, "0x%llx%016llx", (unsigned long long)msi,
+					     (unsigned long long)lsi);
 		break;
+	}
 	case 8:
 		if (sign)
 			btf_dump_type_values(d, "%lld", *(long long *)data);
@@ -2209,7 +2217,7 @@ static int btf_dump_dump_type_data(struct btf_dump *d,
 	case BTF_KIND_ENUM:
 		/* handle bitfield and int enum values */
 		if (bit_sz) {
-			unsigned __int128 print_num;
+			__u64 print_num;
 			__s64 enum_val;
 
 			print_num = btf_dump_bitfield_get_data(d, t, data, bits_offset, bit_sz);
-- 
1.8.3.1