From 239c797090abbdc5253d0ff1e9e657c5006fbbee Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Sat, 6 Feb 2021 10:21:45 -0800 Subject: [PATCH dwarves] btf_encoder: sanitize non-regular int base type 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 Signed-off-by: Yonghong Song --- 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