[PATCH dwarves] btf_encoder: sanitize non-regular int base type

[Yonghong Song <yhs@fb.com>]

clang with dwarf5 may generate non-regular int base type,
i.e., not a signed/unsigned char/short/int/longlong/__int128.
Such base types are often used to describe
how an actual parameter or variable is generated. For example,

0x000015cf:   DW_TAG_base_type
                DW_AT_name      ("DW_ATE_unsigned_1")
                DW_AT_encoding  (DW_ATE_unsigned)
                DW_AT_byte_size (0x00)

0x00010ed9:         DW_TAG_formal_parameter
                      DW_AT_location    (DW_OP_lit0,
                                         DW_OP_not,
                                         DW_OP_convert (0x000015cf) "DW_ATE_unsigned_1",
                                         DW_OP_convert (0x000015d4) "DW_ATE_unsigned_8",
                                         DW_OP_stack_value)
                      DW_AT_abstract_origin     (0x00013984 "branch")

What it does is with a literal "0", did a "not" operation, and the converted to
one-bit unsigned int and then 8-bit unsigned int.

Another example,

0x000e97e4:   DW_TAG_base_type
                DW_AT_name      ("DW_ATE_unsigned_24")
                DW_AT_encoding  (DW_ATE_unsigned)
                DW_AT_byte_size (0x03)

0x000f88f8:     DW_TAG_variable
                  DW_AT_location        (indexed (0x3c) loclist = 0x00008fb0:
                     [0xffffffff82808812, 0xffffffff82808817):
                         DW_OP_breg0 RAX+0,
                         DW_OP_convert (0x000e97d5) "DW_ATE_unsigned_64",
                         DW_OP_convert (0x000e97df) "DW_ATE_unsigned_8",
                         DW_OP_stack_value,
                         DW_OP_piece 0x1,
                         DW_OP_breg0 RAX+0,
                         DW_OP_convert (0x000e97d5) "DW_ATE_unsigned_64",
                         DW_OP_convert (0x000e97da) "DW_ATE_unsigned_32",
                         DW_OP_lit8,
                         DW_OP_shr,
                         DW_OP_convert (0x000e97da) "DW_ATE_unsigned_32",
                         DW_OP_convert (0x000e97e4) "DW_ATE_unsigned_24",
                         DW_OP_stack_value,
                         DW_OP_piece 0x3
                     ......

At one point, a right shift by 8 happens and the result is converted to
32-bit unsigned int and then to 24-bit unsigned int.

BTF does not need any of these DW_OP_* information and such non-regular int
types will cause libbpf to emit errors.
Let us sanitize them to generate BTF acceptable to libbpf and kernel.

Cc: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 libbtf.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/libbtf.c b/libbtf.c
index 9f76283..93fe185 100644
--- a/libbtf.c
+++ b/libbtf.c
@@ -373,6 +373,7 @@ int32_t btf_elf__add_base_type(struct btf_elf *btfe, const struct base_type *bt,
 	struct btf *btf = btfe->btf;
 	const struct btf_type *t;
 	uint8_t encoding = 0;
+	uint16_t byte_sz;
 	int32_t id;
 
 	if (bt->is_signed) {
@@ -384,7 +385,43 @@ int32_t btf_elf__add_base_type(struct btf_elf *btfe, const struct base_type *bt,
 		return -1;
 	}
 
-	id = btf__add_int(btf, name, BITS_ROUNDUP_BYTES(bt->bit_size), encoding);
+	/* dwarf5 may emit DW_ATE_[un]signed_{num} base types where
+	 * {num} is not power of 2 and may exceed 128. Such attributes
+	 * are mostly used to record operation for an actual parameter
+	 * or variable.
+	 * For example,
+	 *     DW_AT_location        (indexed (0x3c) loclist = 0x00008fb0:
+	 *         [0xffffffff82808812, 0xffffffff82808817):
+	 *             DW_OP_breg0 RAX+0,
+	 *             DW_OP_convert (0x000e97d5) "DW_ATE_unsigned_64",
+	 *             DW_OP_convert (0x000e97df) "DW_ATE_unsigned_8",
+	 *             DW_OP_stack_value,
+	 *             DW_OP_piece 0x1,
+	 *             DW_OP_breg0 RAX+0,
+	 *             DW_OP_convert (0x000e97d5) "DW_ATE_unsigned_64",
+	 *             DW_OP_convert (0x000e97da) "DW_ATE_unsigned_32",
+	 *             DW_OP_lit8,
+	 *             DW_OP_shr,
+	 *             DW_OP_convert (0x000e97da) "DW_ATE_unsigned_32",
+	 *             DW_OP_convert (0x000e97e4) "DW_ATE_unsigned_24",
+	 *             DW_OP_stack_value, DW_OP_piece 0x3
+	 *     DW_AT_name    ("ebx")
+	 *     DW_AT_decl_file       ("/linux/arch/x86/events/intel/core.c")
+	 *
+	 * In the above example, at some point, one unsigned_32 value
+	 * is right shifted by 8 and the result is converted to unsigned_32
+	 * and then unsigned_24.
+	 *
+	 * BTF does not need such DW_OP_* information so let us sanitize
+	 * these non-regular int types to avoid libbpf/kernel complaints.
+	 */
+	byte_sz = BITS_ROUNDUP_BYTES(bt->bit_size);
+	if (!byte_sz || (byte_sz & (byte_sz - 1))) {
+		name = "sanitized_int";
+		byte_sz = 4;
+	}
+
+	id = btf__add_int(btf, name, byte_sz, encoding);
 	if (id < 0) {
 		btf_elf__log_err(btfe, BTF_KIND_INT, name, true, "Error emitting BTF type");
 	} else {
-- 
2.24.1