[v2,16/19] gendwarfksyms: Add support for reserved structure fields

Message ID	20240815173903.4172139-37-samitolvanen@google.com (mailing list archive)
State	New
Headers	show Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4729B1BF328 for <linux-kbuild@vger.kernel.org>; Thu, 15 Aug 2024 17:39:43 +0000 (UTC) Date: Thu, 15 Aug 2024 17:39:20 +0000 In-Reply-To: <20240815173903.4172139-21-samitolvanen@google.com> Precedence: bulk Mime-Version: 1.0 References: <20240815173903.4172139-21-samitolvanen@google.com> Message-ID: <20240815173903.4172139-37-samitolvanen@google.com> Subject: [PATCH v2 16/19] gendwarfksyms: Add support for reserved structure fields From: Sami Tolvanen <samitolvanen@google.com> To: Masahiro Yamada <masahiroy@kernel.org>, Luis Chamberlain <mcgrof@kernel.org>, Miguel Ojeda <ojeda@kernel.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Matthew Maurer <mmaurer@google.com>, Alex Gaynor <alex.gaynor@gmail.com>, Wedson Almeida Filho <wedsonaf@gmail.com>, Gary Guo <gary@garyguo.net>, Petr Pavlu <petr.pavlu@suse.com>, Neal Gompa <neal@gompa.dev>, Hector Martin <marcan@marcan.st>, Janne Grunau <j@jannau.net>, Asahi Linux <asahi@lists.linux.dev>, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org, rust-for-linux@vger.kernel.org, Sami Tolvanen <samitolvanen@google.com> Content-Type: text/plain; charset="UTF-8"
Series	Implement DWARF modversions \| expand [v2,00/19] Implement DWARF modversions [v2,01/19] tools: Add gendwarfksyms [v2,02/19] gendwarfksyms: Add symbol list handling [v2,03/19] gendwarfksyms: Add address matching [v2,04/19] gendwarfksyms: Add support for type pointers [v2,05/19] gendwarfksyms: Expand base_type [v2,06/19] gendwarfksyms: Add a cache for processed DIEs [v2,07/19] gendwarfksyms: Expand type modifiers and typedefs [v2,08/19] gendwarfksyms: Expand subroutine_type [v2,09/19] gendwarfksyms: Expand array_type [v2,10/19] gendwarfksyms: Expand structure types [v2,11/19] gendwarfksyms: Limit structure expansion [v2,12/19] gendwarfksyms: Add die_map debugging [v2,13/19] gendwarfksyms: Add symtypes output [v2,14/19] gendwarfksyms: Add symbol versioning [v2,15/19] gendwarfksyms: Add support for declaration-only data structures [v2,16/19] gendwarfksyms: Add support for reserved structure fields [v2,17/19] export: Add __gendwarfksyms_ptr_ references to exported symbols [v2,18/19] x86/asm-prototypes: Include <asm/ptrace.h> [v2,19/19] kbuild: Add gendwarfksyms as an alternative to genksyms

diff --git a/scripts/gendwarfksyms/dwarf.c b/scripts/gendwarfksyms/dwarf.c index bf28946c321e..d6252194692d 100644 --- a/scripts/gendwarfksyms/dwarf.c +++ b/scripts/gendwarfksyms/dwarf.c @@ -274,8 +274,12 @@ int process_die_container(struct state *state, struct die *cache, res = checkp(dwarf_child(die, &current)); while (!res) { - if (match(&current)) - check(func(state, cache, &current)); + if (match(&current)) { + /* <0 = error, 0 = continue, >0 = stop */ + res = checkp(func(state, cache, &current)); + if (res) + return res; + } res = checkp(dwarf_siblingof(&current, &current)); } @@ -490,7 +494,145 @@ static int __process_structure_type(struct state *state, struct die *cache, DEFINE_PROCESS_STRUCTURE_TYPE(class) DEFINE_PROCESS_STRUCTURE_TYPE(structure) -DEFINE_PROCESS_STRUCTURE_TYPE(union) + +static bool is_reserved_member(Dwarf_Die *die) +{ + const char *name = get_name(die); + + return name && !strncmp(name, RESERVED_PREFIX, RESERVED_PREFIX_LEN); +} + +static int __process_reserved_struct(struct state *state, struct die *cache, + Dwarf_Die *die) +{ + Dwarf_Die type; + + /* + * If the union member is a struct, expect the placeholder type to + * be the first member, i.e.: + * + * union { + * type replaced_member; + * struct { + * type placeholder; // <- type + * } + * }; + * + * Stop processing if this member isn't reserved. + */ + if (!is_reserved_member(die)) + return NOT_RESERVED; + + if (!get_ref_die_attr(die, DW_AT_type, &type)) { + error("structure member missing a type?"); + return -1; + } + + check(process_type(state, cache, &type)); + return RESERVED; +} + +static int __process_reserved_union(struct state *state, struct die *cache, + Dwarf_Die *die) +{ + int res = NOT_RESERVED; + Dwarf_Die type; + + if (!get_ref_die_attr(die, DW_AT_type, &type)) { + error("union member missing a type?"); + return -1; + } + + /* + * We expect a union with two members. Check if either of them + * has the reserved name prefix, i.e.: + * + * union { + * ... + * type memberN; // <- type, N = {0,1} + * ... + * }; + * + * The member can also be a structure type, in which case we'll + * check the first structure member. + * + * Stop processing after we've seen two members. + */ + if (is_reserved_member(die)) { + check(process_type(state, cache, &type)); + return RESERVED; + } + + if (dwarf_tag(&type) == DW_TAG_structure_type) + res = checkp(process_die_container(state, cache, &type, + __process_reserved_struct, + match_member_type)); + if (res != RESERVED && ++state->reserved.members < 2) + return 0; /* Continue */ + + return res; +} + +static int process_reserved(struct state *state, struct die *cache, + Dwarf_Die *die) +{ + if (!stable) + return NOT_RESERVED; + + /* + * To maintain a stable kABI, distributions may choose to reserve + * space in structs for later use by adding placeholder members, + * for example: + * + * struct s { + * u64 a; + * // placeholder + * u64 __kabi_reserved_0; + * }; + * + * When the reserved member is taken into use, the type change + * would normally cause the symbol version to change as well, but + * if the replacement uses the following convention, gendwarfksyms + * continues to use the placeholder type for versioning instead, + * thus maintaining the same symbol version: + * + * struct s { + * u64 a; + * union { + * // replaced member + * struct t b; + * struct { + * // original placeholder + * u64 __kabi_reserved_0; + * }; + * }; + * }; + * + * I.e., as long as the replaced member is in a union, and the + * placeholder has a __kabi_reserved name prefix, we'll continue + * to use the placeholder type (here u64) for version calculation + * instead of the union type. + * + * Note that the user is responsible for ensuring that the + * replacement type is ABI compatible with the placeholder type. + */ + state->reserved.members = 0; + + return checkp(process_die_container(state, cache, die, + __process_reserved_union, + match_member_type)); +} + +static int process_union_type(struct state *state, struct die *cache, + Dwarf_Die *die) +{ + if (checkp(process_reserved(state, cache, die)) == RESERVED) + return 0; + + return check(__process_structure_type(state, cache, die, "union_type ", + ___process_structure_type, + match_all)); +} static int process_enumerator_type(struct state *state, struct die *cache, Dwarf_Die *die) diff --git a/scripts/gendwarfksyms/examples/reserved.c b/scripts/gendwarfksyms/examples/reserved.c new file mode 100644 index 000000000000..1e8de7ccd7d2 --- /dev/null +++ b/scripts/gendwarfksyms/examples/reserved.c @@ -0,0 +1,66 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) 2024 Google LLC + * + * Reserved data structure field example. See dwarf.c:process_reserved + * for details. + * + * $ gcc -g -c examples/reserved.c + * + * With --stable, only the reserved field placeholder is used for calculating + * symbol versions. + * + * $ echo exported0 | ./gendwarfksyms --stable --dump-dies reserved.o + * variable structure_type struct0 { + * member base_type int byte_size(4) encoding(5) data_member_location(0), + * member base_type long int byte_size(8) encoding(5) data_member_location(8), + * } byte_size(16) + * + * $ echo exported1 | ./gendwarfksyms --stable --dump-dies reserved.o + * variable structure_type struct1 { + * member base_type int byte_size(4) encoding(5) data_member_location(0), + * member base_type long int byte_size(8) encoding(5) data_member_location(8), + * } byte_size(16) + * + * $ echo exported2 | ./gendwarfksyms --stable --dump-dies reserved.o + * variable structure_type struct2 { + * member base_type int byte_size(4) encoding(5) data_member_location(0), + * member base_type long int byte_size(8) encoding(5) data_member_location(8), + * } byte_size(16) + */ + +struct struct0 { + int a; + union { + long __kabi_reserved_0; + struct { + int b; + int c; + }; + }; +}; + +struct struct1 { + int a; + union { + struct { + int b; + int c; + }; + long __kabi_reserved_1; + }; +}; + +struct struct2 { + int a; + union { + unsigned long b; + struct { + long __kabi_reserved_1; + }; + }; +}; + +struct struct0 exported0; +struct struct1 exported1; +struct struct2 exported2; diff --git a/scripts/gendwarfksyms/gendwarfksyms.h b/scripts/gendwarfksyms/gendwarfksyms.h index 05b5c01b1c2a..963a07167892 100644 --- a/scripts/gendwarfksyms/gendwarfksyms.h +++ b/scripts/gendwarfksyms/gendwarfksyms.h @@ -220,12 +220,27 @@ extern void cache_clear_expanded(struct expansion_cache *ec); /* * dwarf.c */ + +/* See dwarf.c:process_reserved */ +#define RESERVED_PREFIX "__kabi_reserved" +#define RESERVED_PREFIX_LEN (sizeof(RESERVED_PREFIX) - 1) + struct expansion_state { bool expand; bool in_pointer_type; unsigned int ptr_expansion_depth; }; +enum reserved_status { + /* >0 to stop DIE processing */ + NOT_RESERVED = 1, + RESERVED +}; + +struct reserved_state { + int members; +}; + struct state { Dwfl_Module *mod; Dwarf *dbg; @@ -235,6 +250,9 @@ struct state { /* Structure expansion */ struct expansion_state expand; struct expansion_cache expansion_cache; + + /* Reserved members */ + struct reserved_state reserved; }; typedef int (*die_callback_t)(struct state *state, struct die *cache,

[v2,16/19] gendwarfksyms: Add support for reserved structure fields

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