| Here is a summary of changes for the 1.13 version of pahole and its friends: |
| |
| - BTF |
| |
| - Use of the recently introduced BTF deduplication algorithm present in the |
| Linux kernel's libbpf library, which allows for all the types in a multi |
| compile unit binary such as vmlinux to be compactly stored, without duplicates. |
| |
| E.g.: from roughly: |
| |
| $ readelf -SW ../build/v5.1-rc4+/vmlinux | grep .debug_info.*PROGBITS |
| [63] .debug_info PROGBITS 0000000000000000 1d80be0 c3c18b9 00 0 0 1 |
| $ |
| 195 MiB |
| |
| to: |
| |
| $ time pahole --btf_encode ../build/v5.1-rc4+/vmlinux |
| real 0m19.168s |
| user 0m17.707s # On a Lenovo t480s (i7-8650U) SSD |
| sys 0m1.337s |
| $ |
| |
| $ readelf -SW ../build/v5.1-rc4+/vmlinux | grep .BTF.*PROGBITS |
| [78] .BTF PROGBITS 0000000000000000 27b49f61 1e23c3 00 0 0 1 |
| $ |
| ~2 MiB |
| |
| - Introduce a 'btfdiff' utility that prints the output from DWARF and from |
| BTF, comparing the pretty printed outputs, running it on various linux |
| kernel images, such as an allyesconfig for ppc64. |
| |
| Running it on the above 5.1-rc4+ vmlinux: |
| |
| $ btfdiff ../build/v5.1-rc4+/vmlinux |
| $ |
| |
| No differences from the types generated from the DWARF ELF sections to the |
| ones generated from the BTF ELF section. |
| |
| - Add a BTF loader, i.e. 'pahole -F btf' allows pretty printing of structs |
| and unions in the same fashion as with DWARF info, and since BTF is way |
| more compact, using it is much faster than using DWARF. |
| |
| $ cat ../build/v5.1-rc4+/vmlinux > /dev/null |
| $ perf stat -e cycles pahole -F btf ../build/v5.1-rc4+/vmlinux > /dev/null |
| |
| Performance counter stats for 'pahole -F btf ../build/v5.1-rc4+/vmlinux': |
| |
| 229,712,692 cycles:u |
| 0.063379597 seconds time elapsed |
| 0.056265000 seconds user |
| 0.006911000 seconds sys |
| |
| $ perf stat -e cycles pahole -F dwarf ../build/v5.1-rc4+/vmlinux > /dev/null |
| |
| Performance counter stats for 'pahole -F dwarf ../build/v5.1-rc4+/vmlinux': |
| |
| 49,579,679,466 cycles:u |
| 13.063487352 seconds time elapsed |
| 12.612512000 seconds user |
| 0.426226000 seconds sys |
| $ |
| |
| - Better union support: |
| |
| - Allow unions to be specified in pahole in the same fashion as structs |
| |
| $ pahole -C thread_union ../build/v5.1-rc4+/net/ipv4/tcp.o |
| union thread_union { |
| struct task_struct task __attribute__((__aligned__(64))); /* 0 11008 */ |
| long unsigned int stack[2048]; /* 0 16384 */ |
| }; |
| $ |
| |
| - Infer __attribute__((__packed__)) when structs have no alignment holes |
| and violate basic types (integer, longs, short integer) natural alignment |
| requirements. Several heuristics are used to infer the __packed__ |
| attribute, see the changeset log for descriptions. |
| |
| $ pahole -F btf -C boot_e820_entry ../build/v5.1-rc4+/vmlinux |
| struct boot_e820_entry { |
| __u64 addr; /* 0 8 */ |
| __u64 size; /* 8 8 */ |
| __u32 type; /* 16 4 */ |
| |
| /* size: 20, cachelines: 1, members: 3 */ |
| /* last cacheline: 20 bytes */ |
| } __attribute__((__packed__)); |
| $ |
| |
| $ pahole -F btf -C lzma_header ../build/v5.1-rc4+/vmlinux |
| struct lzma_header { |
| uint8_t pos; /* 0 1 */ |
| uint32_t dict_size; /* 1 4 */ |
| uint64_t dst_size; /* 5 8 */ |
| |
| /* size: 13, cachelines: 1, members: 3 */ |
| /* last cacheline: 13 bytes */ |
| } __attribute__((__packed__)); |
| |
| - Support DWARF5's DW_AT_alignment, which, together with the __packed__ |
| attribute inference algorithms produce output that, when compiled, should |
| produce structures with layouts that match the original source code. |
| |
| See it in action with 'struct task_struct', which will also show some of the |
| new information at the struct summary, at the end of the struct: |
| |
| $ pahole -C task_struct ../build/v5.1-rc4+/vmlinux | tail -19 |
| /* --- cacheline 103 boundary (6592 bytes) --- */ |
| struct vm_struct * stack_vm_area; /* 6592 8 */ |
| refcount_t stack_refcount; /* 6600 4 */ |
| |
| /* XXX 4 bytes hole, try to pack */ |
| |
| void * security; /* 6608 8 */ |
| |
| /* XXX 40 bytes hole, try to pack */ |
| |
| /* --- cacheline 104 boundary (6656 bytes) --- */ |
| struct thread_struct thread __attribute__((__aligned__(64))); /* 6656 4352 */ |
| |
| /* size: 11008, cachelines: 172, members: 207 */ |
| /* sum members: 10902, holes: 16, sum holes: 98 */ |
| /* sum bitfield members: 10 bits, bit holes: 2, sum bit holes: 54 bits */ |
| /* paddings: 3, sum paddings: 14 */ |
| /* forced alignments: 6, forced holes: 1, sum forced holes: 40 */ |
| } __attribute__((__aligned__(64))); |
| $ |
| |
| - Add a '--compile' option to 'pfunct' that produces compileable output for the |
| function prototypes in an object file. There are still some bugs but the vast |
| majority of the kernel single compilation unit files the ones produced from a |
| single .c file are working, see the new 'fullcircle' utility that uses this |
| feature. |
| |
| Example of it in action: |
| |
| $ pfunct --compile=static_key_false ../build/v5.1-rc4+/net/ipv4/tcp.o |
| typedef _Bool bool; |
| typedef struct { |
| int counter; /* 0 4 */ |
| |
| /* size: 4, cachelines: 1, members: 1 */ |
| /* last cacheline: 4 bytes */ |
| } atomic_t; |
| |
| struct jump_entry; |
| |
| struct static_key_mod; |
| |
| |
| struct static_key { |
| atomic_t enabled; /* 0 4 */ |
| |
| /* XXX 4 bytes hole, try to pack */ |
| |
| union { |
| long unsigned int type; /* 8 8 */ |
| struct jump_entry * entries; /* 8 8 */ |
| struct static_key_mod * next; /* 8 8 */ |
| }; /* 8 8 */ |
| |
| /* size: 16, cachelines: 1, members: 2 */ |
| /* sum members: 12, holes: 1, sum holes: 4 */ |
| /* last cacheline: 16 bytes */ |
| }; |
| |
| bool static_key_false(struct static_key * key) |
| { |
| return *(bool *)1; |
| } |
| |
| $ |
| |
| The generation of compilable code from the type information and its use in the |
| new tool 'fullcircle, helps validate all the parts of this codebase, finding |
| bugs that were lurking forever, go read the csets to find all sorts of curious |
| C language features that are rarely seen, like unnamed zero sized bitfields and |
| the way people have been using it over the years in a codebase like the linux |
| kernel. |
| |
| Certainly there are several other features, changes and fixes that I forgot to |
| mention! Now lemme release this version so that we can use it more extensively |
| together with a recent patch merged for 5.2: |
| |
| [PATCH bpf-next] kbuild: add ability to generate BTF type info for vmlinux |
| |
| With it BTF will be always available for all the types of the kernel, which will |
| open a pandora box of cool new features that are in the works, and, for people |
| already using pahole, will greatly speed up its usage. |
| |
| Please try to alias it to use btf, i.e. |
| |
| alias pahole='pahole -F btf' |
| |
| Please report any problems you may find with this new version or with the BTF |
| loader or any errors in the layout generated/pretty printed. |
| |
| Thanks to the fine BTF guys at Facebook for the patches and help in testing, |
| fixing bugs and getting this out of the door, the stats for this release are: |
| |
| Changesets: 157 |
| |
| 113 Arnaldo Carvalho de Melo Red Hat |
| 32 Andrii Nakryiko Facebook |
| 10 Yonghong Song Facebook |
| 1 Martin Lau Facebook |
| 1 Domenico Andreoli |
