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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.

Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Mark Wielaard <mark@klomp.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Yonghong Song 2021-02-06 23:17:26 -08:00 committed by Arnaldo Carvalho de Melo
parent 0d415f68c4
commit 7d8e829f63
1 changed files with 38 additions and 1 deletions
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39
libbtf.c
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@ -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_FAKE_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 {