From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (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 07E901FF1CE for ; Thu, 19 Dec 2024 21:08:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734642497; cv=none; b=DAu4LRy8i5YcTgnjNw56bOaB2OSi81weaJ7lfuzH6CoPLXSmxZp6bINOCWc5/F2/HLwn9TplHJv3If6EOyn8EDXbgUnTnXyB9SbjuVxFTpIAWSjE8pcvlSu4f7u11eegowqzK9bBProSE1h4TzrwiW+I+XdPeCygmy/xdlKqChE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734642497; c=relaxed/simple; bh=meWJOhPVkswEJEUPXpRMtDuGyzKKL9cF0sOOnTujhIQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=QVN0OYyop4/lSPvTnXKeJm8dgD0hDLP5QxCwhvVgetD/DRittl3IuAQ59elliI1Sn/wCWowcsSvNc3LDyzbn3TXLniknVLDmZkycdfvndgX/rUOQ+E8+ohMO+p2tdjPN+Ozbe6YAwu9CG6FOdQ69XMAbXSYNNtP8rEVBP+yQ/0s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--samitolvanen.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=2PKkc+tW; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--samitolvanen.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="2PKkc+tW" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2ef7fbd99a6so1079880a91.1 for ; Thu, 19 Dec 2024 13:08:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1734642494; x=1735247294; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=BJ+bQtpgXwuh9TDVVL7KrLC8CdDggoJteu7mzxqQJxM=; b=2PKkc+tWijCOqRnr4WXcjJfj3mOQGjm+17rpOKvfesZTYu1U+Evo74tUZ9mfSQnRVg +gEmg4OEy/GwpRZrry6CBSYypSxHwr1oGqSel2xgVm+PFWJnAt+oKR4o9YGtgMcmGzTV lJcmbZQbIFbm95pLaG4bdorOC4NSNi+c6hETnZlLBGMwpr5+n5pqETw1dPxTGWWHn+tZ wbipKx8B+0FmqIgCOXmv7hKAynQ/bVedPncjLq+35wQUUeEWU2NO8VaXgjp4cxD4ZJNM oYQg9DsVpQ2iFOHYlEQvo7Bq94j+/TggbYatZnS6DsHaSJCyT0Y3c9IchYUFTH+XzHDn 4u8Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1734642494; x=1735247294; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=BJ+bQtpgXwuh9TDVVL7KrLC8CdDggoJteu7mzxqQJxM=; b=FIU6ehiTpmNjKa8LZ/+j4WCzYf7fWhprHfInWKLq08Rw4XwAVsbSjReDxC1phWC4Ty wto3M0i95Z7BVcX64+CfNTgwupiTt+8KHDEjaSutyWdO0R5oFGGviFILlR991EzvtMv4 JvNNFWFyuxUEZyfoBoTt4Xn3KSXorAHdUsmqMPPsd1lg1APh2LircL36jq5xhoxG7aQ0 wUqKdV5L372keMXHBWV3OOhrpPd58q9am7XWZJS21kBHc/osTigDSmIuiBd8/zkBbLcT 3JL4t9dfHkQvEtbJWftASmU7EEpuWHFvc5HO9STbN+Uq97b4+gNm1xm+rjAT3yzMdH8T 6egA== X-Forwarded-Encrypted: i=1; AJvYcCWUd0uyJxjsw5Oqqa/+XNz76BZMMc1srPz/Ee5k4AjsGygcw97rQsLRnvBJXC5W1r1VuSQBsi60fi0uLpdp@vger.kernel.org X-Gm-Message-State: AOJu0YwEUN07l2qZ7Q+eyGYK7gtt4YoFXCcfi29oau02a05nAn9Cnw2q sWEAcQuc41DuQn1EvUOtMX34/EQolVQ2sMMFbuMqmIx8tsKlvppPPf83VMOCDVXRydFoyjoEBBy ylV85qFg7jcHp0zyj54eDiBYC7g== X-Google-Smtp-Source: AGHT+IFanGBqP4nFKDIDHoYd02bX7Fby8FIHEYxpEIjfOOg6TCvJOUA3qQnwUsNt2GWM+nb/JBf8ycMhpKxFRcd5rHY= X-Received: from pjur4.prod.google.com ([2002:a17:90a:d404:b0:2ea:448a:8cd1]) (user=samitolvanen job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2c84:b0:2ee:f687:6ad5 with SMTP id 98e67ed59e1d1-2f452dfd364mr694606a91.2.1734642494365; Thu, 19 Dec 2024 13:08:14 -0800 (PST) Date: Thu, 19 Dec 2024 21:07:52 +0000 In-Reply-To: <20241219210736.2990838-20-samitolvanen@google.com> Precedence: bulk X-Mailing-List: linux-modules@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241219210736.2990838-20-samitolvanen@google.com> X-Developer-Key: i=samitolvanen@google.com; a=openpgp; fpr=35CCFB63B283D6D3AEB783944CB5F6848BBC56EE X-Developer-Signature: v=1; a=openpgp-sha256; l=7893; i=samitolvanen@google.com; h=from:subject; bh=meWJOhPVkswEJEUPXpRMtDuGyzKKL9cF0sOOnTujhIQ=; b=owGbwMvMwCEWxa662nLh8irG02pJDOkp3QprJt5xy297p+c4h5v117ka+5XB987+nDhz06mHm dN25DyW6ChlYRDjYJAVU2Rp+bp66+7vTqmvPhdJwMxhZQIZwsDFKQATCatk+O86J7wpnmP2Zu1e a4Xb6XMiPx9g6g7SO5uSXyOrtErK/Scjw48HUbsbE/gOnHgc4NU6rbVnBtvKhd+LvX9vXzh/1+K WfA4A X-Mailer: git-send-email 2.47.1.613.gc27f4b7a9f-goog Message-ID: <20241219210736.2990838-35-samitolvanen@google.com> Subject: [PATCH v7 15/18] gendwarfksyms: Add support for symbol type pointers From: Sami Tolvanen To: Masahiro Yamada , Luis Chamberlain , Miguel Ojeda , Greg Kroah-Hartman Cc: Matthew Maurer , Alex Gaynor , Gary Guo , Petr Pavlu , Daniel Gomez , Neal Gompa , Hector Martin , Janne Grunau , Miroslav Benes , Asahi Linux , Sedat Dilek , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org, rust-for-linux@vger.kernel.org, Sami Tolvanen Content-Type: text/plain; charset="UTF-8" The compiler may choose not to emit type information in DWARF for external symbols. Clang, for example, does this for symbols not defined in the current TU. To provide a way to work around this issue, add support for __gendwarfksyms_ptr_ pointers that force the compiler to emit the necessary type information in DWARF also for the missing symbols. Example usage: #define GENDWARFKSYMS_PTR(sym) \ static typeof(sym) *__gendwarfksyms_ptr_##sym __used \ __section(".discard.gendwarfksyms") = &sym; extern int external_symbol(void); GENDWARFKSYMS_PTR(external_symbol); Signed-off-by: Sami Tolvanen Reviewed-by: Petr Pavlu --- scripts/gendwarfksyms/dwarf.c | 55 +++++++++++++++++++++- scripts/gendwarfksyms/examples/symbolptr.c | 33 +++++++++++++ scripts/gendwarfksyms/gendwarfksyms.h | 7 +++ scripts/gendwarfksyms/symbols.c | 27 +++++++++++ 4 files changed, 121 insertions(+), 1 deletion(-) create mode 100644 scripts/gendwarfksyms/examples/symbolptr.c diff --git a/scripts/gendwarfksyms/dwarf.c b/scripts/gendwarfksyms/dwarf.c index 746a89d9e3d4..534d9aa7c114 100644 --- a/scripts/gendwarfksyms/dwarf.c +++ b/scripts/gendwarfksyms/dwarf.c @@ -1061,6 +1061,31 @@ static void process_variable(struct state *state, Dwarf_Die *die) process_symbol(state, die, __process_variable); } +static void save_symbol_ptr(struct state *state) +{ + Dwarf_Die ptr_type; + Dwarf_Die type; + + if (!get_ref_die_attr(&state->die, DW_AT_type, &ptr_type) || + dwarf_tag(&ptr_type) != DW_TAG_pointer_type) + error("%s must be a pointer type!", + get_symbol_name(&state->die)); + + if (!get_ref_die_attr(&ptr_type, DW_AT_type, &type)) + error("%s pointer missing a type attribute?", + get_symbol_name(&state->die)); + + /* + * Save the symbol pointer DIE in case the actual symbol is + * missing from the DWARF. Clang, for example, intentionally + * omits external symbols from the debugging information. + */ + if (dwarf_tag(&type) == DW_TAG_subroutine_type) + symbol_set_ptr(state->sym, &type); + else + symbol_set_ptr(state->sym, &ptr_type); +} + static int process_exported_symbols(struct state *unused, struct die *cache, Dwarf_Die *die) { @@ -1084,7 +1109,9 @@ static int process_exported_symbols(struct state *unused, struct die *cache, state_init(&state); - if (tag == DW_TAG_subprogram) + if (is_symbol_ptr(get_symbol_name(&state.die))) + save_symbol_ptr(&state); + else if (tag == DW_TAG_subprogram) process_subprogram(&state, &state.die); else process_variable(&state, &state.die); @@ -1097,10 +1124,36 @@ static int process_exported_symbols(struct state *unused, struct die *cache, } } +static void process_symbol_ptr(struct symbol *sym, void *arg) +{ + struct state state; + Dwarf *dwarf = arg; + + if (sym->state != SYMBOL_UNPROCESSED || !sym->ptr_die_addr) + return; + + debug("%s", sym->name); + state_init(&state); + state.sym = sym; + + if (!dwarf_die_addr_die(dwarf, (void *)sym->ptr_die_addr, &state.die)) + error("dwarf_die_addr_die failed for symbol ptr: '%s'", + sym->name); + + if (dwarf_tag(&state.die) == DW_TAG_subroutine_type) + process_subprogram(&state, &state.die); + else + process_variable(&state, &state.die); + + cache_free(&state.expansion_cache); +} + void process_cu(Dwarf_Die *cudie) { check(process_die_container(NULL, NULL, cudie, process_exported_symbols, match_all)); + symbol_for_each(process_symbol_ptr, dwarf_cu_getdwarf(cudie->cu)); + cache_free(&srcfile_cache); } diff --git a/scripts/gendwarfksyms/examples/symbolptr.c b/scripts/gendwarfksyms/examples/symbolptr.c new file mode 100644 index 000000000000..88bc1bd60da8 --- /dev/null +++ b/scripts/gendwarfksyms/examples/symbolptr.c @@ -0,0 +1,33 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2024 Google LLC + * + * Example for symbol pointers. When compiled with Clang, gendwarfkyms + * uses a symbol pointer for `f`. + * + * $ clang -g -c examples/symbolptr.c -o examples/symbolptr.o + * $ echo -e "f\ng\np" | ./gendwarfksyms -d examples/symbolptr.o + */ + +/* Kernel macros for userspace testing. */ +#ifndef __used +#define __used __attribute__((__used__)) +#endif +#ifndef __section +#define __section(section) __attribute__((__section__(section))) +#endif + +#define __GENDWARFKSYMS_EXPORT(sym) \ + static typeof(sym) *__gendwarfksyms_ptr_##sym __used \ + __section(".discard.gendwarfksyms") = &sym; + +extern void f(unsigned int arg); +void g(int *arg); +void g(int *arg) {} + +struct s; +extern struct s *p; + +__GENDWARFKSYMS_EXPORT(f); +__GENDWARFKSYMS_EXPORT(g); +__GENDWARFKSYMS_EXPORT(p); diff --git a/scripts/gendwarfksyms/gendwarfksyms.h b/scripts/gendwarfksyms/gendwarfksyms.h index fe49730fe623..197a1a8123c6 100644 --- a/scripts/gendwarfksyms/gendwarfksyms.h +++ b/scripts/gendwarfksyms/gendwarfksyms.h @@ -89,6 +89,10 @@ extern int symtypes; * symbols.c */ +/* See symbols.c:is_symbol_ptr */ +#define SYMBOL_PTR_PREFIX "__gendwarfksyms_ptr_" +#define SYMBOL_PTR_PREFIX_LEN (sizeof(SYMBOL_PTR_PREFIX) - 1) + static inline unsigned int addr_hash(uintptr_t addr) { return hash_ptr((const void *)addr); @@ -112,14 +116,17 @@ struct symbol { struct hlist_node name_hash; enum symbol_state state; uintptr_t die_addr; + uintptr_t ptr_die_addr; unsigned long crc; }; typedef void (*symbol_callback_t)(struct symbol *, void *arg); +bool is_symbol_ptr(const char *name); void symbol_read_exports(FILE *file); void symbol_read_symtab(int fd); struct symbol *symbol_get(const char *name); +void symbol_set_ptr(struct symbol *sym, Dwarf_Die *ptr); void symbol_set_die(struct symbol *sym, Dwarf_Die *die); void symbol_set_crc(struct symbol *sym, unsigned long crc); void symbol_for_each(symbol_callback_t func, void *arg); diff --git a/scripts/gendwarfksyms/symbols.c b/scripts/gendwarfksyms/symbols.c index 4c499ba6c86d..327f87389c34 100644 --- a/scripts/gendwarfksyms/symbols.c +++ b/scripts/gendwarfksyms/symbols.c @@ -39,6 +39,20 @@ static unsigned int __for_each_addr(struct symbol *sym, symbol_callback_t func, return processed; } +/* + * For symbols without debugging information (e.g. symbols defined in other + * TUs), we also match __gendwarfksyms_ptr_ symbols, which the + * kernel uses to ensure type information is present in the TU that exports + * the symbol. A __gendwarfksyms_ptr pointer must have the same type as the + * exported symbol, e.g.: + * + * typeof(symname) *__gendwarf_ptr_symname = &symname; + */ +bool is_symbol_ptr(const char *name) +{ + return name && !strncmp(name, SYMBOL_PTR_PREFIX, SYMBOL_PTR_PREFIX_LEN); +} + static unsigned int for_each(const char *name, symbol_callback_t func, void *data) { @@ -47,6 +61,8 @@ static unsigned int for_each(const char *name, symbol_callback_t func, if (!name || !*name) return 0; + if (is_symbol_ptr(name)) + name += SYMBOL_PTR_PREFIX_LEN; hash_for_each_possible_safe(symbol_names, match, tmp, name_hash, hash_str(name)) { @@ -84,6 +100,17 @@ void symbol_set_crc(struct symbol *sym, unsigned long crc) error("no matching symbols: '%s'", sym->name); } +static void set_ptr(struct symbol *sym, void *data) +{ + sym->ptr_die_addr = (uintptr_t)((Dwarf_Die *)data)->addr; +} + +void symbol_set_ptr(struct symbol *sym, Dwarf_Die *ptr) +{ + if (for_each(sym->name, set_ptr, ptr) == 0) + error("no matching symbols: '%s'", sym->name); +} + static void set_die(struct symbol *sym, void *data) { sym->die_addr = (uintptr_t)((Dwarf_Die *)data)->addr; -- 2.47.1.613.gc27f4b7a9f-goog