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@xxxxxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
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
