Re: Fedora kernel enabling Rust

[Alan Maguire <alan.maguire@oracle.com>]

On 17/10/2024 23:03, Arnaldo Carvalho de Melo wrote:
> Hi,
> 
> 	While testing the latest patches on a fedora 40 system I
> noticed:
> 
>   Compilation Unit @ offset 0x77fda3d:
>    Length:        0xd527 (32-bit)
>    Version:       5
>    Unit Type:     DW_UT_compile (1)
>    Abbrev Offset: 0x38012d
>    Pointer Size:  8
>  <0><77fda49>: Abbrev Number: 6 (DW_TAG_compile_unit)
>     <77fda4a>   DW_AT_producer    : (indirect string, offset: 0x4ec527): GNU C11 14.2.1 20240912 (Red Hat 14.2.1-3) -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -mno-80387 -mno-fp-ret
> -in-387 -mpreferred-stack-boundary=3 -mskip-rax-setup -mtune=generic -mno-red-zone -mcmodel=kernel -mindirect-branch=thunk-extern -mindirect-branch-register -mindirect-branch-cs-prefix -mfunc
> tion-return=thunk-extern -mharden-sls=all -mrecord-mcount -mfentry -march=x86-64 -g -O2 -std=gnu11 -p -fshort-wchar -funsigned-char -fno-common -fno-PIE -fno-strict-aliasing -fcf-protection=b
> ranch -falign-jumps=1 -falign-loops=1 -fno-asynchronous-unwind-tables -fno-jump-tables -fpatchable-function-entry=16,16 -fno-delete-null-pointer-checks -fno-allow-store-data-races -fstack-pro
> tector-strong -ftrivial-auto-var-init=zero -fno-stack-clash-protection -fmin-function-alignment=16 -fstrict-flex-arrays=3 -fno-strict-overflow -fstack-check=no -fconserve-stack -fsanitize=bou
> nds-strict -fsanitize=shift
>     <77fda4e>   DW_AT_language    : 29  (C11)
>     <77fda4f>   DW_AT_name        : (indirect line string, offset: 0xfa3e): rust/exports.c
>     <77fda53>   DW_AT_comp_dir    : (indirect line string, offset: 0x4db): /usr/src/debug/kernel-6.11.3/linux-6.11.3-200.fc40.x86_64
> <SNIP>
>     <78078ce>   DW_AT_name        : (indirect string, offset: 0x5310d): __UNIQUE_ID___addressable__RNvXshK_NtCshatLywNUlpX_8bindings12bindings_rawNtB6_28mei_connect_client_data_vtagNtNtCs2vSfyxKMEZc_4core7default7Default7default1222
>     <78078d2>   DW_AT_decl_file   : 4
>     <78078d3>   DW_AT_decl_line   : 740
>     <78078d5>   DW_AT_decl_column : 1
>     <78078d5>   DW_AT_type        : <0x77fdac9>
>     <78078d9>   DW_AT_location    : 9 byte block: 3 0 0 0 0 0 0 0 0     (DW_OP_addr: 0)
>  <1><78078e3>: Abbrev Number: 1 (DW_TAG_variable)
>     <78078e4>   DW_AT_name        : (indirect string, offset: 0x51af69): _RNvXshL_NtCshatLywNUlpX_8bindings12bindings_rawNtB6_13hda_device_idNtNtCs2vSfyxKMEZc_4core7default7Default7default
>     <78078e8>   DW_AT_decl_file   : 4
>     <78078e9>   DW_AT_decl_line   : 741
>     <78078eb>   DW_AT_decl_column : 1
>     <78078eb>   DW_AT_type        : <0x77fda8c>
>     <78078ef>   DW_AT_external    : 1
>     <78078ef>   DW_AT_declaration : 1
>  <1><78078ef>: Abbrev Number: 2 (DW_TAG_variable)
>     <78078f0>   DW_AT_name        : (indirect string, offset: 0x83a79): __UNIQUE_ID___addressable__RNvXshL_NtCshatLywNUlpX_8bindings12bindings_rawNtB6_13hda_device_idNtNtCs2vSfyxKMEZc_4core7default7Default7default1223
> 
> That caused:
> 
> acme@number:~/git/pahole$ tests/btf_functions.sh 
> Validation of BTF encoding of functions; this may take some time: PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXsa_NtCs2vSfyxKMEZc_4core4charNtB5_11EscapeDebugNtNtNtNtB7_4iter6traits10exact_size17ExactSizeIterator3len57').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXse_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits8iterator8Iterator4next59').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXse_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits8iterator8Iterator9size_hint60').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXse_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits8iterator8Iterator5count61').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXse_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits8iterator8Iterator4last62').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXse_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits8iterator8Iterator10advance_by63').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXsf_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits12double_ended19DoubleEndedIterator9next_back64').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXsf_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits12double_ended19DoubleEndedIterator15advance_back_by65').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXsg_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits10exact_size17ExactSizeIterator3len66').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXsg_NtCs2vSfyxKMEZc_4core4charNtB5_15CaseMappingIterNtNtNtNtB7_4iter6traits10exact_size17ExactSizeIterator8is_empty67').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXs0_NtNtCs2vSfyxKMEZc_4core3net6parserNtNtB7_7ip_addr6IpAddrNtNtNtB9_3str6traits7FromStr8from_str95').
> PAHOLE: Warning: Found invalid variable name when encoding btf, ignored (sym: '__UNIQUE_ID___addressable__RNvXs2_NtNtCs2vSfyxKMEZc_4core3net6parserNtNtB7_7ip_addr8Ipv4AddrNtNtNtB9_3str6traits7FromStr8from_str97').
> 
> 
> At first I thought that was from Rust source code, but nope, its things
> in C to connect to Rust, have you guys thought about this? The warning
> is not that good, invalid why? Lenght of the symbol name?
> 
> Its the end of my work day, so I have yet to think this through, so just
> reporting it here to initiate a discussion.
> 
> acme@number:~/git/pahole$ grep RUST /boot/config-6.11.3-200.fc40.x86_64 
> CONFIG_RUST_IS_AVAILABLE=y
> CONFIG_RUST=y
> CONFIG_RUSTC_VERSION_TEXT="rustc 1.81.0 (eeb90cda1 2024-09-04) (Fedora 1.81.0-1.fc40)"
> CONFIG_HAVE_RUST=y
> CONFIG_RUST_FW_LOADER_ABSTRACTIONS=y
> CONFIG_BLK_DEV_RUST_NULL=m
> CONFIG_RUST_PHYLIB_ABSTRACTIONS=y
> CONFIG_AX88796B_RUST_PHY=y
> CONFIG_HID_THRUSTMASTER=m
> CONFIG_THRUSTMASTER_FF=y
> CONFIG_TRUSTED_KEYS=y
> CONFIG_HAVE_TRUSTED_KEYS=y
> CONFIG_TRUSTED_KEYS_TPM=y
> CONFIG_INTEGRITY_TRUSTED_KEYRING=y
> CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT=y
> CONFIG_SYSTEM_TRUSTED_KEYRING=y
> # CONFIG_SYSTEM_TRUSTED_KEYS="certs/rhel.pem"
> CONFIG_SYSTEM_TRUSTED_KEYS=""
> CONFIG_SECONDARY_TRUSTED_KEYRING=y
> # CONFIG_SECONDARY_TRUSTED_KEYRING_SIGNED_BY_BUILTIN is not set
> # CONFIG_RUST_DEBUG_ASSERTIONS is not set
> CONFIG_RUST_OVERFLOW_CHECKS=y
> # CONFIG_RUST_BUILD_ASSERT_ALLOW is not set
> acme@number:~/git/pahole$
>

hi Arnaldo,

thanks for the report! This is as you suspected due to the name being
longer than KSYM_NAME_LEN as checked by btf_name_valid(), but we should
skip it anyway as __UNIQUE_ID is one of the filter prefixes we skip in
encoding. If we just reorder the checks we can avoid these warnings I
think. I've sent a patch for that [1]; if you could test it (or can
point me at a vmlinux with the symbols I can do so) that would be great.
Thanks!

Alan

[1]
https://lore.kernel.org/dwarves/20241018094301.1550149-1-alan.maguire@oracle.com/