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([185.25.67.249]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a99a80f2446sm551817766b.206.2024.10.14.01.53.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Oct 2024 01:53:44 -0700 (PDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d27c7779-8a09-11ef-a0be-8be0dac302b0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloud.com; s=cloud; t=1728896025; x=1729500825; darn=lists.xenproject.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=uF49wRium9i4EoXLYTW2SLTmEeikurwbqD9tKvn/ty4=; b=COvIKQ+KWp3XB3Fq0Qf/jwzqqX/tNqqrruZT/EMz/FU4Xnrb5R1/rsUah57TnTx87U mfgvrLr+5KuHNvuGuA1MOvV+GkI+D2h/IRLM/WlyWj1vmXQ/ACqHHqCJZX5FBirCAuEy xRGDpuPmJ4QFnWX6GhEXAen8W3HvVhCnlkNT8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1728896025; x=1729500825; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=uF49wRium9i4EoXLYTW2SLTmEeikurwbqD9tKvn/ty4=; b=nmEDRPH8dc3TW9z4fcM0p8Q1oAhAIVGoYkmGQA+rJtKibt8vosv+YtbIwwA/CGAyL6 EnmuA/okBdt4LeELXTeMdHqf3a/wHHqHshG/KiF9b2n0VFPZIJYrB9cIf0kCogiWIoH7 b9NCfkb6Hp5BGRBBABiaIZSiNaSBxcHy/K2VjhPbv2sH9dDkO+qg9BOCZ9lxArFCdlqj 3V4Iu2DsPwn7T6v5Uxs3VKrswtSnFVtP0X+VhkX/x0jcMKmG6rn1h0PreCq0Lqm3fpH8 Y8EmKdyEV25+nenqBlEPT0bpggSncPrMxtXPuHDcJ23CCfd1nAeh7+VBk870PMBHzPk4 4P2w== X-Gm-Message-State: AOJu0Ywv4FCuwXjXF30zQwS7+1nVXg04mGN8rIBJ4/Km6TY+5EUJRC2E M+Ek9SIGH861C+RZBws2JjLQXxpNNWAWpO9yrtH2Gmwmp4Nu2PHKsGk9M3xJdBqSilHsFskc1pv h X-Google-Smtp-Source: AGHT+IH5ZbWN//oAAR1E4EBGs18FbAmIUsa7vCFIn2id5C5jlMOVBB9J9wqwvM57wwc+bXFYmWcktg== X-Received: by 2002:a17:907:84d:b0:a99:e939:d69e with SMTP id a640c23a62f3a-a99e939d95bmr684155466b.51.1728896025231; Mon, 14 Oct 2024 01:53:45 -0700 (PDT) From: Frediano Ziglio To: xen-devel@lists.xenproject.org Cc: Frediano Ziglio , Jan Beulich , Andrew Cooper , =?utf-8?q?Roger_Pau_Monn=C3=A9?= , Julien Grall , Stefano Stabellini Subject: [PATCH v4 2/6] x86/boot: create a C bundle for 32 bit boot code and use it Date: Mon, 14 Oct 2024 09:53:28 +0100 Message-Id: <20241014085332.3254546-3-frediano.ziglio@cloud.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20241014085332.3254546-1-frediano.ziglio@cloud.com> References: <20241014085332.3254546-1-frediano.ziglio@cloud.com> MIME-Version: 1.0 The current method to include 32 bit C boot code is: - compile each function we want to use into a separate object file; - each function is compiled with -fpic option; - convert these object files to binary files. This operation removes GOP which we don't want in the executable; - a small assembly part in each file add the entry point; - code can't have external references, all possible variables are passed by value or pointer; - include these binary files in head.S. There are currently some limitations: - code is compiled separately, it's not possible to share a function (like memcpy) between different functions to use; - although code is compiled with -fpic there's no certainty there are no relocations, specifically data ones. This can lead into hard to find bugs; - it's hard to add a simple function; - having to pass external variables makes hard to do multiple things otherwise functions would require a lot of parameters so code would have to be split into multiple functions which is not easy. Current change extends the current process: - all object files are linked together before getting converted making possible to share code between the function we want to call; - a single object file is generated with all functions to use and exported symbols to easily call; - variables to use are declared in linker script and easily used inside C code. Declaring them manually could be annoying but makes also easier to check them. Using external pointers can be still an issue if they are not fixed. If an external symbol is not declared this gives a link error. Some details of the implementation: - C code is compiled with -fpic flags (as before); - object files from C code are linked together; - the single bundled object file is linked with 2 slightly different script files to generate 2 bundled object files; - the 2 bundled object files are converted to binary removing the need for global offset tables; - a Python script is used to generate assembly source from the 2 binaries; - the single assembly file is compiled to generate final bundled object file; - to detect possible unwanted relocation in data/code code is generated with different addresses. This is enforced starting .text section at different positions and adding a fixed "gap" at the beginning. This makes sure code and data is position independent; - to detect used symbols in data/code symbols are placed in .text section at different offsets (based on the line in the linker script). This is needed as potentially a reference to a symbol is converted to a reference to the containing section so multiple symbols could be converted to reference to same symbol (section name) and we need to distinguish them; - --orphan-handling=error option to linker is used to make sure we account for all possible sections from C code; Current limitations: - the main one is the lack of support for 64 bit code. It would make sure that even the code used for 64 bit (at the moment EFI code) is code and data position independent. We cannot assume that code that came from code compiled for 32 bit and compiled for 64 bit is code and data position independent, different compiler options lead to different code/data. Signed-off-by: Frediano Ziglio --- Changes since v2: - removed W^X limitation, allowing data; - added some comments to python script; - added extension to python script; - added header to generated assembly code from python script; - added starting symbol to generated assembly code from python script to make disassembly more clear; - other minor style changes to python script. --- xen/arch/x86/boot/.gitignore | 5 +- xen/arch/x86/boot/Makefile | 38 +++- .../x86/boot/{build32.lds => build32.lds.S} | 35 ++- xen/arch/x86/boot/cmdline.c | 12 - xen/arch/x86/boot/head.S | 12 - xen/arch/x86/boot/reloc.c | 14 -- xen/tools/combine_two_binaries.py | 207 ++++++++++++++++++ 7 files changed, 268 insertions(+), 55 deletions(-) rename xen/arch/x86/boot/{build32.lds => build32.lds.S} (70%) create mode 100755 xen/tools/combine_two_binaries.py diff --git a/xen/arch/x86/boot/.gitignore b/xen/arch/x86/boot/.gitignore index a379db7988..ebad650e5c 100644 --- a/xen/arch/x86/boot/.gitignore +++ b/xen/arch/x86/boot/.gitignore @@ -1,3 +1,4 @@ /mkelf32 -/*.bin -/*.lnk +/build32.*.lds +/built_in_32.*.bin +/built_in_32.*.map diff --git a/xen/arch/x86/boot/Makefile b/xen/arch/x86/boot/Makefile index 1199291d2b..23ad274c89 100644 --- a/xen/arch/x86/boot/Makefile +++ b/xen/arch/x86/boot/Makefile @@ -1,4 +1,5 @@ obj-bin-y += head.o +obj-bin-y += built_in_32.o obj32 := cmdline.32.o obj32 += reloc.32.o @@ -9,9 +10,6 @@ targets += $(obj32) obj32 := $(addprefix $(obj)/,$(obj32)) -$(obj)/head.o: AFLAGS-y += -Wa$(comma)-I$(obj) -$(obj)/head.o: $(obj32:.32.o=.bin) - CFLAGS_x86_32 := $(subst -m64,-m32 -march=i686,$(XEN_TREEWIDE_CFLAGS)) $(call cc-options-add,CFLAGS_x86_32,CC,$(EMBEDDED_EXTRA_CFLAGS)) CFLAGS_x86_32 += -Werror -fno-builtin -g0 -msoft-float -mregparm=3 @@ -25,14 +23,34 @@ $(obj32): XEN_CFLAGS := $(CFLAGS_x86_32) -fpic $(obj)/%.32.o: $(src)/%.c FORCE $(call if_changed_rule,cc_o_c) +orphan-handling-$(call ld-option,--orphan-handling=error) := --orphan-handling=error LDFLAGS_DIRECT-$(call ld-option,--warn-rwx-segments) := --no-warn-rwx-segments LDFLAGS_DIRECT += $(LDFLAGS_DIRECT-y) LD32 := $(LD) $(subst x86_64,i386,$(LDFLAGS_DIRECT)) -%.bin: %.lnk - $(OBJCOPY) -j .text -O binary $< $@ - -%.lnk: %.32.o $(src)/build32.lds - $(LD32) -N -T $(filter %.lds,$^) -o $@ $< - -clean-files := *.lnk *.bin +$(obj)/build32.final.lds: AFLAGS-y += -DFINAL +$(obj)/build32.other.lds $(obj)/build32.final.lds: $(src)/build32.lds.S FORCE + $(call if_changed_dep,cpp_lds_S) + +# link all 32bit objects together +$(obj)/built_in_32.tmp.o: $(obj32) + $(LD32) -r -o $@ $^ + +$(obj)/built_in_32.%.bin: $(obj)/build32.%.lds $(obj)/built_in_32.tmp.o +## link bundle with a given layout + $(LD32) $(orphan-handling-y) -N -T $< -Map $(obj)/built_in_32.$(*F).map -o $(obj)/built_in_32.$(*F).o $(obj)/built_in_32.tmp.o +## extract binaries from object + $(OBJCOPY) -j .text -O binary $(obj)/built_in_32.$(*F).o $@ + rm -f $(obj)/built_in_32.$(*F).o + +# generate final object file combining and checking above binaries +$(obj)/built_in_32.S: $(obj)/built_in_32.other.bin $(obj)/built_in_32.final.bin + $(PYTHON) $(srctree)/tools/combine_two_binaries.py \ + --script $(obj)/build32.final.lds \ + --bin1 $(obj)/built_in_32.other.bin \ + --bin2 $(obj)/built_in_32.final.bin \ + --map $(obj)/built_in_32.final.map \ + --exports cmdline_parse_early,reloc \ + --output $@ + +clean-files := built_in_32.*.bin built_in_32.*.map build32.*.lds diff --git a/xen/arch/x86/boot/build32.lds b/xen/arch/x86/boot/build32.lds.S similarity index 70% rename from xen/arch/x86/boot/build32.lds rename to xen/arch/x86/boot/build32.lds.S index 56edaa727b..50c167aef0 100644 --- a/xen/arch/x86/boot/build32.lds +++ b/xen/arch/x86/boot/build32.lds.S @@ -15,22 +15,47 @@ * with this program. If not, see . */ -ENTRY(_start) +#ifdef FINAL +# define GAP 0 +# define MULT 0 +# define TEXT_START +#else +# define GAP 0x010200 +# define MULT 1 +# define TEXT_START 0x408020 +#endif +# define DECLARE_IMPORT(name) name = . + (__LINE__ * MULT) + +ENTRY(dummy_start) SECTIONS { /* Merge code and data into one section. */ - .text : { + .text TEXT_START : { + /* Silence linker warning, we are not going to use it */ + dummy_start = .; + + /* Declare below any symbol name needed. + * Each symbol should be on its own line. + * It looks like a tedious work but we make sure the things we use. + * Potentially they should be all variables. */ + DECLARE_IMPORT(__base_relocs_start); + DECLARE_IMPORT(__base_relocs_end); + . = . + GAP; *(.text) *(.text.*) - *(.data) - *(.data.*) *(.rodata) *(.rodata.*) + *(.data) + *(.data.*) *(.bss) *(.bss.*) } - + /DISCARD/ : { + *(.comment) + *(.comment.*) + *(.note.*) + } /* Dynamic linkage sections. Collected simply so we can check they're empty. */ .got : { *(.got) diff --git a/xen/arch/x86/boot/cmdline.c b/xen/arch/x86/boot/cmdline.c index fc9241ede9..196c580e91 100644 --- a/xen/arch/x86/boot/cmdline.c +++ b/xen/arch/x86/boot/cmdline.c @@ -18,18 +18,6 @@ * Linux kernel source (linux/lib/string.c). */ -/* - * This entry point is entered from xen/arch/x86/boot/head.S with: - * - %eax = &cmdline, - * - %edx = &early_boot_opts. - */ -asm ( - " .text \n" - " .globl _start \n" - "_start: \n" - " jmp cmdline_parse_early \n" - ); - #include #include #include diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S index c4de1dfab5..e0776e3896 100644 --- a/xen/arch/x86/boot/head.S +++ b/xen/arch/x86/boot/head.S @@ -759,18 +759,6 @@ trampoline_setup: /* Jump into the relocated trampoline. */ lret - /* - * cmdline and reloc are written in C, and linked to be 32bit PIC with - * entrypoints at 0 and using the fastcall convention. - */ -FUNC_LOCAL(cmdline_parse_early) - .incbin "cmdline.bin" -END(cmdline_parse_early) - -FUNC_LOCAL(reloc) - .incbin "reloc.bin" -END(reloc) - ENTRY(trampoline_start) #include "trampoline.S" ENTRY(trampoline_end) diff --git a/xen/arch/x86/boot/reloc.c b/xen/arch/x86/boot/reloc.c index 8c58affcd9..94b078d7b1 100644 --- a/xen/arch/x86/boot/reloc.c +++ b/xen/arch/x86/boot/reloc.c @@ -12,20 +12,6 @@ * Daniel Kiper */ -/* - * This entry point is entered from xen/arch/x86/boot/head.S with: - * - %eax = MAGIC, - * - %edx = INFORMATION_ADDRESS, - * - %ecx = TOPMOST_LOW_MEMORY_STACK_ADDRESS. - * - 0x04(%esp) = BOOT_VIDEO_INFO_ADDRESS. - */ -asm ( - " .text \n" - " .globl _start \n" - "_start: \n" - " jmp reloc \n" - ); - #include #include #include diff --git a/xen/tools/combine_two_binaries.py b/xen/tools/combine_two_binaries.py new file mode 100755 index 0000000000..138c59287e --- /dev/null +++ b/xen/tools/combine_two_binaries.py @@ -0,0 +1,207 @@ +#!/usr/bin/env python3 + +from __future__ import print_function +import argparse +import re +import struct +import sys + +parser = argparse.ArgumentParser(description='Generate assembly file to merge into other code.') +parser.add_argument('--script', dest='script', + required=True, + help='Linker script for extracting symbols') +parser.add_argument('--bin1', dest='bin1', + required=True, + help='First binary') +parser.add_argument('--bin2', dest='bin2', + required=True, + help='Second binary') +parser.add_argument('--output', dest='output', + help='Output file') +parser.add_argument('--map', dest='mapfile', + help='Map file to read for symbols to export') +parser.add_argument('--exports', dest='exports', + help='Symbols to export') +parser.add_argument('--section-header', dest='section_header', + default='.section .init.text, "ax", @progbits', + help='Section header declaration') +parser.add_argument('-v', '--verbose', + action='store_true') +args = parser.parse_args() + +gap = 0x010200 +text_diff = 0x408020 + +# Parse linker script for external symbols to use. +# Next regex matches expanded DECLARE_IMPORT lines in linker script. +symbol_re = re.compile(r'\s+(\S+)\s*=\s*\.\s*\+\s*\((\d+)\s*\*\s*0\s*\)\s*;') +symbols = {} +lines = {} +for line in open(args.script): + m = symbol_re.match(line) + if not m: + continue + (name, line_num) = (m.group(1), int(m.group(2))) + if line_num == 0: + raise Exception("Invalid line number found:\n\t" + line) + if line_num in symbols: + raise Exception("Symbol with this line already present:\n\t" + line) + if name in lines: + raise Exception("Symbol with this name already present:\n\t" + name) + symbols[line_num] = name + lines[name] = line_num + +exports = [] +if args.exports is not None: + exports = dict([(name, None) for name in args.exports.split(',')]) + +# Parse mapfile, look for ther symbols we want to export. +if args.mapfile is not None: + symbol_re = re.compile(r'\s{15,}0x([0-9a-f]+)\s+(\S+)\n') + for line in open(args.mapfile): + m = symbol_re.match(line) + if not m or m.group(2) not in exports: + continue + addr = int(m.group(1), 16) + exports[m.group(2)] = addr +for (name, addr) in exports.items(): + if addr is None: + raise Exception("Required export symbols %s not found" % name) + +file1 = open(args.bin1, 'rb') +file2 = open(args.bin2, 'rb') +file1.seek(0, 2) +size1 = file1.tell() +file2.seek(0, 2) +size2 = file2.tell() +if size1 > size2: + file1, file2 = file2, file1 + size1, size2 = size2, size1 +if size2 != size1 + gap: + raise Exception('File sizes do not match') + +file1.seek(0, 0) +data1 = file1.read(size1) +file2.seek(gap, 0) +data2 = file2.read(size1) + +max_line = max(symbols.keys()) + +def to_int32(n): + '''Convert a number to signed 32 bit integer truncating if needed''' + mask = (1 << 32) - 1 + h = 1 << 31 + return (n & mask) ^ h - h + +i = 0 +references = {} +internals = 0 +while i <= size1 - 4: + n1 = struct.unpack('= 10: + break + continue + # This is a relative relocation to a symbol, accepted, code/data is + # relocatable. + if diff < gap and diff >= gap - max_line: + n = gap - diff + symbol = symbols.get(n) + # check we have a symbol + if symbol is None: + raise Exception("Cannot find symbol for line %d" % n) + pos = i - 1 + if args.verbose: + print('Position %#x %d %s' % (pos, n, symbol), file=sys.stderr) + i += 3 + references[pos] = symbol + continue + # First byte is the same, move to next byte + if diff & 0xff == 0 and i <= size1 - 4: + continue + # Probably a type of relocation we don't want or support + pos = i - 1 + suggestion = '' + symbol = symbols.get(-diff - text_diff) + if symbol is not None: + suggestion = " Maybe %s is not defined as hidden?" % symbol + raise Exception("Unexpected difference found at %#x " + "n1=%#x n2=%#x diff=%#x gap=%#x.%s" % \ + (pos, n1, n2, diff, gap, suggestion)) +if internals != 0: + raise Exception("Previous relocations found") + +def line_bytes(buf, out): + '''Output an assembly line with all bytes in "buf"''' + # Python 2 compatibility + if type(buf) == str: + print("\t.byte " + ','.join([str(ord(c)) for c in buf]), file=out) + else: + print("\t.byte " + ','.join([str(n) for n in buf]), file=out) + +def part(start, end, out): + '''Output bytes of "data" from "start" to "end"''' + while start < end: + e = min(start + 16, end) + line_bytes(data1[start:e], out) + start = e + +def reference(pos, out): + name = references[pos] + n = struct.unpack('= (1 << 31): + n -= (1 << 32) + n += pos + if n < 0: + n = -n + sign = '-' + print("\t.hidden %s\n" + "\t.long %s %s %#x - ." % (name, name, sign, n), + file=out) + +def output(out): + prev = 0 + exports_by_addr = {} + for (sym, addr) in exports.items(): + exports_by_addr.setdefault(addr, []).append(sym) + positions = list(references.keys()) + positions += list(exports_by_addr.keys()) + for pos in sorted(positions): + part(prev, pos, out) + prev = pos + if pos in references: + reference(pos, out) + prev = pos + 4 + if pos in exports_by_addr: + for sym in exports_by_addr[pos]: + print("\t.global %s\n" + "\t.hidden %s\n" + "%s:" % (sym, sym, sym), + file=out) + part(prev, size1, out) + +out = sys.stdout +if args.output is not None: + out = open(args.output, 'w') +print('''/* + * File autogenerated by combine_two_binaries.py DO NOT EDIT + */''', file=out) +print('\t' + args.section_header, file=out) +print('obj_start:', file=out) +output(out) +print('\n\t.section\t.note.GNU-stack,"",@progbits', file=out) +out.flush()