Re: ERROR: INT DW_ATE_unsigned_1 Error emitting BTF type
From: Yonghong Song
Date: Sat Feb 06 2021 - 15:15:00 EST
On 2/6/21 11:44 AM, Sedat Dilek wrote:
On Sat, Feb 6, 2021 at 8:33 PM Yonghong Song <yhs@xxxxxx> wrote:
On 2/6/21 11:28 AM, Sedat Dilek wrote:
On Sat, Feb 6, 2021 at 8:22 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
On Sat, Feb 6, 2021 at 8:17 PM Yonghong Song <yhs@xxxxxx> wrote:
On 2/6/21 10:10 AM, Sedat Dilek wrote:
On Sat, Feb 6, 2021 at 6:53 PM Yonghong Song <yhs@xxxxxx> wrote:
On 2/6/21 8:24 AM, Mark Wieelard wrote:
Hi,
On Sat, Feb 06, 2021 at 12:26:44AM -0800, Yonghong Song wrote:
With the above vmlinux, the issue appears to be handling
DW_ATE_signed_1, DW_ATE_unsigned_{1,24,40}.
The following patch should fix the issue:
That doesn't really make sense to me. Why is the compiler emitting a
DW_TAG_base_type that needs to be interpreted according to the
DW_AT_name attribute?
If the issue is that the size of the base type cannot be expressed in
bytes then the DWARF spec provides the following option:
If the value of an object of the given type does not fully occupy
the storage described by a byte size attribute, the base type
entry may also have a DW_AT_bit_size and a DW_AT_data_bit_offset
attribute, both of whose values are integer constant values (see
Section 2.19 on page 55). The bit size attribute describes the
actual size in bits used to represent values of the given
type. The data bit offset attribute is the offset in bits from the
beginning of the containing storage to the beginning of the
value. Bits that are part of the offset are padding. If this
attribute is omitted a default data bit offset of zero is assumed.
Would it be possible to use that encoding of those special types? If
I agree with you. I do not like comparing me as well. Unfortunately,
there is no enough information in dwarf to find out actual information.
The following is the dwarf dump with vmlinux (Sedat provided) for
DW_ATE_unsigned_1.
0x000e97e9: DW_TAG_base_type
DW_AT_name ("DW_ATE_unsigned_1")
DW_AT_encoding (DW_ATE_unsigned)
DW_AT_byte_size (0x00)
There is no DW_AT_bit_size and DW_AT_bit_offset for base type.
AFAIK, these two attributes typically appear in struct/union members
together with DW_AT_byte_size.
Maybe compilers (clang in this case) can emit DW_AT_bit_size = 1
and DW_AT_bit_offset = 0/7 (depending on big/little endian) and
this case, we just test and get DW_AT_bit_size and it should work.
But I think BTF does not need this (DW_ATE_unsigned_1) for now.
I checked dwarf dump and it is mostly used for some arith operation
encoded in dump (in this case, e.g., shift by 1 bit)
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")
Look at clang frontend, only the following types are encoded with
unsigned dwarf type.
case BuiltinType::UShort:
case BuiltinType::UInt:
case BuiltinType::UInt128:
case BuiltinType::ULong:
case BuiltinType::WChar_U:
case BuiltinType::ULongLong:
Encoding = llvm::dwarf::DW_ATE_unsigned;
break;
not, can we try to come up with some extension that doesn't require
consumers to match magic names?
You want me to upload mlx5_core.ko?
I just sent out a patch. You are cc'ed. I also attached in this email.
Yes, it would be great if you can upload mlx5_core.ko so I can
double check with this DW_ATE_unsigned_160 which is really usual.
Yupp, just built a new pahole :-).
Re-building linux-kernel...
Will upload mlx5_core.ko - need zstd-ed it before.
Hmm, I guess you want a mlx5_core.ko with your patch applied-to-pahole-1.20 :-)?
this should work too. I want to check dwarf data. My patch won't impact
dwarf generation.
Usual Dropbox-Link:
https://www.dropbox.com/sh/kvyh8ps7na0r1h5/AABfyNfDZ2bESse_bo4h05fFa?dl=0
See "for-yhs" directory:
1. mlx5-module_yhs-v1 ("[PATCH dwarves] btf_encoder: sanitize
non-regular int base type")
2. mlx5-module_yhs-dileks-v4 (with the last diff-v4 I tried successfully)
Thanks, with llvm-dwarfdump, I can see
0x00d65616: DW_TAG_base_type
DW_AT_name ("DW_ATE_unsigned_160")
DW_AT_encoding (DW_ATE_unsigned)
DW_AT_byte_size (0x14)
0x00d88e81: DW_TAG_variable
DW_AT_location (indexed (0xad) loclist =
0x0005df42:
[0x0000000000088c8e, 0x0000000000088c97):
DW_OP_breg9 R9+0, DW_OP_convert (0x00d65616) "DW_ATE_unsigned_160",
DW_OP_convert (0x00d65607) "DW_ATE_unsigned_32", DW_OP_stack_value,
DW_OP_piece 0x4)
DW_AT_abstract_origin (0x00d88d37 "_v")
0x00d88d37: DW_TAG_variable
DW_AT_name ("_v")
DW_AT_decl_file
("/home/dileks/src/linux-kernel/git/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_ste.c")
DW_AT_decl_line (1198)
DW_AT_type (0x00d68835 "u32")
The source code at line 1198.
1198 DR_STE_SET_MASK_V(eth_l3_ipv4_5_tuple, bit_mask,
1199 source_port, mask, udp_sport);
This is for struct mlx5dr_match_spec.
struct mlx5dr_match_spec {
u32 smac_47_16; /* Source MAC address of incoming packet */
/* Incoming packet Ethertype - this is the Ethertype
* following the last VLAN tag of the packet
*/
u32 ethertype:16;
u32 smac_15_0:16;
...
u32 tcp_dport:16;
/* TCP source port.;tcp and udp sport/dport are mutually
exclusive */
u32 tcp_sport:16;
u32 ttl_hoplimit:8;
u32 reserved:24;
/* UDP destination port.;tcp and udp sport/dport are mutually
exclusive */
u32 udp_dport:16;
/* UDP source port.;tcp and udp sport/dport are mutually
exclusive */
u32 udp_sport:16;
/* IPv6 source address of incoming packets
* For IPv4 address use bits 31:0 (rest of the bits are reserved)
* This field should be qualified by an appropriate ethertype
*/
u32 src_ip_127_96;
...
}
which includes a bunch of bit fields and non-bit fields.
I have no idea why clang will generate
DW_OP_convert (0x00d65616) "DW_ATE_unsigned_160"
and possibly try to capture more semantic information?
But BTF should be able to safely ignore this as described
in my patch.
Thanks.
- Sedat -
- Sedat -
When looking with llvm-dwarf for DW_ATE_unsigned_160:
0x00d65616: DW_TAG_base_type
DW_AT_name ("DW_ATE_unsigned_160")
DW_AT_encoding (DW_ATE_unsigned)
DW_AT_byte_size (0x14)
If you need further information, please let me know.
Thanks.
- Sedat -