From patchwork Mon Feb 8 17:57:48 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ard Biesheuvel X-Patchwork-Id: 580451 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [103.22.144.68]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id C7E03140761 for ; Tue, 9 Feb 2016 05:05:03 +1100 (AEDT) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linaro.org header.i=@linaro.org header.b=IGFy6vW2; dkim-atps=neutral Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 9DD5F1A02EF for ; Tue, 9 Feb 2016 05:05:03 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linaro.org header.i=@linaro.org header.b=IGFy6vW2; dkim-atps=neutral X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Received: from mail-wm0-x22c.google.com (mail-wm0-x22c.google.com [IPv6:2a00:1450:400c:c09::22c]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 47A6B1A028E for ; Tue, 9 Feb 2016 04:58:06 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linaro.org header.i=@linaro.org header.b=IGFy6vW2; dkim-atps=neutral Received: by mail-wm0-x22c.google.com with SMTP id p63so126887317wmp.1 for ; Mon, 08 Feb 2016 09:58:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=slSyxulaDZgSqu3FegWbWXGKq5lGB6sPsP06ppHUjJ0=; b=IGFy6vW2212ce4hMw4m8ppvg65EleOFgj332i588Iv185SVjf+B+eZTCLOHTmIMjkx udB/ys86pG71rWTgJ5J5tqYLv8AnaGjhrDVuZ9JUuTLHM2YMCJWrROhjv1ObBhs5g3Ty LFGHaXCrSvXeTF4G6o+czOivsSpddLuTez1jE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=slSyxulaDZgSqu3FegWbWXGKq5lGB6sPsP06ppHUjJ0=; b=c5sgYbDvknGcyzuenJDew0Ny/emoW4kUMsjGGT1GFiPTHpaQF09EjRnwVzkoKgLajk UwLrI+sqDaUvxZILEfGC9Hga/8MR2rdIzAAW44HO8iRTJ2Ixkmz9j+/34RUAsA+l35WM v0MWRl35cgI132MYMGPdpKGdH0SGtYJMlTpb/ot9w0GjmJqcKYFgLOXqiK0Jsjs1lWPD tf1SWSZ6s8U0Qc/EU/mhK3OgSz4C86SFjh47r4LNkZCf0vLI2XjwhkwhhMoiZ89yIyGT EYFHDVFG57rYajPJv3kGUkOoXuXB/WgCSGZM6tExHpCaCx1OaA5bnJa8y8GAzrNbZsrI dcVA== X-Gm-Message-State: AG10YOQYstYMNkH8B419RLenJim44jRaoQuzgZPyuIz+S1OrrHA/hZ0UQomHeJKQZHzPxFet X-Received: by 10.28.93.140 with SMTP id r134mr135188wmb.80.1454954283157; Mon, 08 Feb 2016 09:58:03 -0800 (PST) Received: from localhost.localdomain ([195.55.142.58]) by smtp.gmail.com with ESMTPSA id w17sm13664684wmw.5.2016.02.08.09.58.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 08 Feb 2016 09:58:02 -0800 (PST) From: Ard Biesheuvel To: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, keescook@chromium.org, akpm@linux-foundation.org, mingo@kernel.org, hpa@zytor.com, heiko.carstens@de.ibm.com, benh@kernel.crashing.org, mpe@ellerman.id.au, mmarek@suse.cz, rusty@rustcorp.com.au, arnd@arndb.de, linux-arch@vger.kernel.org, linux@roeck-us.net Subject: [PATCH v5 3/3] kallsyms: add support for relative offsets in kallsyms address table Date: Mon, 8 Feb 2016 18:57:48 +0100 Message-Id: <1454954268-3225-4-git-send-email-ard.biesheuvel@linaro.org> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1454954268-3225-1-git-send-email-ard.biesheuvel@linaro.org> References: <1454954268-3225-1-git-send-email-ard.biesheuvel@linaro.org> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Ard Biesheuvel MIME-Version: 1.0 Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Similar to how relative extables are implemented, it is possible to emit the kallsyms table in such a way that it contains offsets relative to some anchor point in the kernel image rather than absolute addresses. On 64-bit architectures, it cuts the size of the kallsyms address table in half, since offsets between kernel symbols can typically be expressed in 32 bits. This saves several hundreds of kilobytes of permanent .rodata on average. In addition, the kallsyms address table is no longer subject to dynamic relocation when CONFIG_RELOCATABLE is in effect, so the relocation work done after decompression now doesn't have to do relocation updates for all these values. This saves up to 24 bytes (i.e., the size of a ELF64 RELA relocation table entry) per value, which easily adds up to a couple of megabytes of uncompressed __init data on ppc64 or arm64. Even if these relocation entries typically compress well, the combined size reduction of 2.8 MB uncompressed for a ppc64_defconfig build (of which 2.4 MB is __init data) results in a ~500 KB space saving in the compressed image. Since it is useful for some architectures (like x86) to retain the ability to emit absolute values as well, this patch also adds support for capturing both absolute and relative values when KALLSYMS_ABSOLUTE_PERCPU is in effect, by emitting absolute per-cpu addresses as positive 32-bit values, and addresses relative to the lowest encountered relative symbol as negative values, which are subtracted from the runtime address of this base symbol to produce the actual address. Support for the above is enabled by default for all architectures except IA-64 and Tile-GX, whose symbols are too far apart to capture in this manner. Signed-off-by: Ard Biesheuvel --- init/Kconfig | 18 ++++ kernel/kallsyms.c | 42 +++++++-- scripts/kallsyms.c | 89 +++++++++++++++++--- scripts/link-vmlinux.sh | 4 + scripts/namespace.pl | 2 + 5 files changed, 136 insertions(+), 19 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index b17824a875fa..6d48682fbcae 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1424,6 +1424,24 @@ config KALLSYMS_ABSOLUTE_PERCPU bool default X86_64 && SMP +config KALLSYMS_BASE_RELATIVE + bool + depends on KALLSYMS + default !IA64 && !(TILE && 64BIT) + help + Instead of emitting them as absolute values in the native word size, + emit the symbol references in the kallsyms table as 32-bit entries, + each containing a relative value in the range [base, base + U32_MAX] + or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either + an absolute value in the range [0, S32_MAX] or a relative value in the + range [base, base + S32_MAX], where base is the lowest relative symbol + address encountered in the image. + + On 64-bit builds, this reduces the size of the address table by 50%, + but more importantly, it results in entries whose values are build + time constants, and no relocation pass is required at runtime to fix + up the entries based on the runtime load address of the kernel. + config PRINTK default y bool "Enable support for printk" if EXPERT diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 5c5987f10819..fafd1a3ef0da 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -38,6 +38,7 @@ * during the second link stage. */ extern const unsigned long kallsyms_addresses[] __weak; +extern const int kallsyms_offsets[] __weak; extern const u8 kallsyms_names[] __weak; /* @@ -47,6 +48,9 @@ extern const u8 kallsyms_names[] __weak; extern const unsigned long kallsyms_num_syms __attribute__((weak, section(".rodata"))); +extern const unsigned long kallsyms_relative_base +__attribute__((weak, section(".rodata"))); + extern const u8 kallsyms_token_table[] __weak; extern const u16 kallsyms_token_index[] __weak; @@ -176,6 +180,23 @@ static unsigned int get_symbol_offset(unsigned long pos) return name - kallsyms_names; } +static unsigned long kallsyms_sym_address(int idx) +{ + if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE)) + return kallsyms_addresses[idx]; + + /* values are unsigned offsets if --absolute-percpu is not in effect */ + if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU)) + return kallsyms_relative_base + (u32)kallsyms_offsets[idx]; + + /* ...otherwise, positive offsets are absolute values */ + if (kallsyms_offsets[idx] >= 0) + return kallsyms_offsets[idx]; + + /* ...and negative offsets are relative to kallsyms_relative_base - 1 */ + return kallsyms_relative_base - 1 - kallsyms_offsets[idx]; +} + /* Lookup the address for this symbol. Returns 0 if not found. */ unsigned long kallsyms_lookup_name(const char *name) { @@ -187,7 +208,7 @@ unsigned long kallsyms_lookup_name(const char *name) off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); if (strcmp(namebuf, name) == 0) - return kallsyms_addresses[i]; + return kallsyms_sym_address(i); } return module_kallsyms_lookup_name(name); } @@ -204,7 +225,7 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *, for (i = 0, off = 0; i < kallsyms_num_syms; i++) { off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); - ret = fn(data, namebuf, NULL, kallsyms_addresses[i]); + ret = fn(data, namebuf, NULL, kallsyms_sym_address(i)); if (ret != 0) return ret; } @@ -220,7 +241,10 @@ static unsigned long get_symbol_pos(unsigned long addr, unsigned long i, low, high, mid; /* This kernel should never had been booted. */ - BUG_ON(!kallsyms_addresses); + if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE)) + BUG_ON(!kallsyms_addresses); + else + BUG_ON(!kallsyms_offsets); /* Do a binary search on the sorted kallsyms_addresses array. */ low = 0; @@ -228,7 +252,7 @@ static unsigned long get_symbol_pos(unsigned long addr, while (high - low > 1) { mid = low + (high - low) / 2; - if (kallsyms_addresses[mid] <= addr) + if (kallsyms_sym_address(mid) <= addr) low = mid; else high = mid; @@ -238,15 +262,15 @@ static unsigned long get_symbol_pos(unsigned long addr, * Search for the first aliased symbol. Aliased * symbols are symbols with the same address. */ - while (low && kallsyms_addresses[low-1] == kallsyms_addresses[low]) + while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low)) --low; - symbol_start = kallsyms_addresses[low]; + symbol_start = kallsyms_sym_address(low); /* Search for next non-aliased symbol. */ for (i = low + 1; i < kallsyms_num_syms; i++) { - if (kallsyms_addresses[i] > symbol_start) { - symbol_end = kallsyms_addresses[i]; + if (kallsyms_sym_address(i) > symbol_start) { + symbol_end = kallsyms_sym_address(i); break; } } @@ -470,7 +494,7 @@ static unsigned long get_ksymbol_core(struct kallsym_iter *iter) unsigned off = iter->nameoff; iter->module_name[0] = '\0'; - iter->value = kallsyms_addresses[iter->pos]; + iter->value = kallsyms_sym_address(iter->pos); iter->type = kallsyms_get_symbol_type(off); diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c index d39a1eeb080e..073d4601b982 100644 --- a/scripts/kallsyms.c +++ b/scripts/kallsyms.c @@ -22,6 +22,7 @@ #include #include #include +#include #ifndef ARRAY_SIZE #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0])) @@ -43,6 +44,7 @@ struct addr_range { }; static unsigned long long _text; +static unsigned long long relative_base; static struct addr_range text_ranges[] = { { "_stext", "_etext" }, { "_sinittext", "_einittext" }, @@ -62,6 +64,7 @@ static int all_symbols = 0; static int absolute_percpu = 0; static char symbol_prefix_char = '\0'; static unsigned long long kernel_start_addr = 0; +static int base_relative = 0; int token_profit[0x10000]; @@ -75,7 +78,7 @@ static void usage(void) fprintf(stderr, "Usage: kallsyms [--all-symbols] " "[--symbol-prefix=] " "[--page-offset=] " - "< in.map > out.S\n"); + "[--base-relative] < in.map > out.S\n"); exit(1); } @@ -205,6 +208,8 @@ static int symbol_valid(struct sym_entry *s) */ static char *special_symbols[] = { "kallsyms_addresses", + "kallsyms_offsets", + "kallsyms_relative_base", "kallsyms_num_syms", "kallsyms_names", "kallsyms_markers", @@ -349,16 +354,48 @@ static void write_src(void) printf("\t.section .rodata, \"a\"\n"); - /* Provide proper symbols relocatability by their '_text' - * relativeness. The symbol names cannot be used to construct - * normal symbol references as the list of symbols contains - * symbols that are declared static and are private to their - * .o files. This prevents .tmp_kallsyms.o or any other - * object from referencing them. + /* Provide proper symbols relocatability by their relativeness + * to a fixed anchor point in the runtime image, either '_text' + * for absolute address tables, in which case the linker will + * emit the final addresses at build time. Otherwise, use the + * offset relative to the lowest value encountered of all relative + * symbols, and emit non-relocatable fixed offsets that will be fixed + * up at runtime. + * + * The symbol names cannot be used to construct normal symbol + * references as the list of symbols contains symbols that are + * declared static and are private to their .o files. This prevents + * .tmp_kallsyms.o or any other object from referencing them. */ - output_label("kallsyms_addresses"); + if (!base_relative) + output_label("kallsyms_addresses"); + else + output_label("kallsyms_offsets"); + for (i = 0; i < table_cnt; i++) { - if (!symbol_absolute(&table[i])) { + if (base_relative) { + long long offset; + int overflow; + + if (!absolute_percpu) { + offset = table[i].addr - relative_base; + overflow = (offset < 0 || offset > UINT_MAX); + } else if (symbol_absolute(&table[i])) { + offset = table[i].addr; + overflow = (offset < 0 || offset > INT_MAX); + } else { + offset = relative_base - table[i].addr - 1; + overflow = (offset < INT_MIN || offset >= 0); + } + if (overflow) { + fprintf(stderr, "kallsyms failure: " + "%s symbol value %#llx out of range in relative mode\n", + symbol_absolute(&table[i]) ? "absolute" : "relative", + table[i].addr); + exit(EXIT_FAILURE); + } + printf("\t.long\t%#x\n", (int)offset); + } else if (!symbol_absolute(&table[i])) { if (_text <= table[i].addr) printf("\tPTR\t_text + %#llx\n", table[i].addr - _text); @@ -371,6 +408,12 @@ static void write_src(void) } printf("\n"); + if (base_relative) { + output_label("kallsyms_relative_base"); + printf("\tPTR\t_text - %#llx\n", _text - relative_base); + printf("\n"); + } + output_label("kallsyms_num_syms"); printf("\tPTR\t%d\n", table_cnt); printf("\n"); @@ -695,6 +738,18 @@ static void make_percpus_absolute(void) } } +/* find the minimum non-absolute symbol address */ +static void record_relative_base(void) +{ + unsigned int i; + + relative_base = -1ULL; + for (i = 0; i < table_cnt; i++) + if (!symbol_absolute(&table[i]) && + table[i].addr < relative_base) + relative_base = table[i].addr; +} + int main(int argc, char **argv) { if (argc >= 2) { @@ -713,7 +768,9 @@ int main(int argc, char **argv) } else if (strncmp(argv[i], "--page-offset=", 14) == 0) { const char *p = &argv[i][14]; kernel_start_addr = strtoull(p, NULL, 16); - } else + } else if (strcmp(argv[i], "--base-relative") == 0) + base_relative = 1; + else usage(); } } else if (argc != 1) @@ -722,6 +779,8 @@ int main(int argc, char **argv) read_map(stdin); if (absolute_percpu) make_percpus_absolute(); + if (base_relative) + record_relative_base(); sort_symbols(); optimize_token_table(); write_src(); diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index 7a08bf9a9576..453ede9d2f3d 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -90,6 +90,10 @@ kallsyms() kallsymopt="${kallsymopt} --absolute-percpu" fi + if [ -n "${CONFIG_KALLSYMS_BASE_RELATIVE}" ]; then + kallsymopt="${kallsymopt} --base-relative" + fi + local aflags="${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \ ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}" diff --git a/scripts/namespace.pl b/scripts/namespace.pl index a71be6b7cdec..9f3c9d47a4a5 100755 --- a/scripts/namespace.pl +++ b/scripts/namespace.pl @@ -117,6 +117,8 @@ my %nameexception = ( 'kallsyms_names' => 1, 'kallsyms_num_syms' => 1, 'kallsyms_addresses'=> 1, + 'kallsyms_offsets' => 1, + 'kallsyms_relative_base'=> 1, '__this_module' => 1, '_etext' => 1, '_edata' => 1,