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    Subject[PATCH AUTOSEL 5.5 412/542] x86/boot/compressed: Relax sed symbol type regex for LLVM ld.lld
    Date
    From: Ard Biesheuvel <ardb@kernel.org>

    [ Upstream commit bc310baf2ba381c648983c7f4748327f17324562 ]

    The final build stage of the x86 kernel captures some symbol
    addresses from the decompressor binary and copies them into zoffset.h.
    It uses sed with a regular expression that matches the address, symbol
    type and symbol name, and mangles the captured addresses and the names
    of symbols of interest into #define directives that are added to
    zoffset.h

    The symbol type is indicated by a single letter, which we match
    strictly: only letters in the set 'ABCDGRSTVW' are matched, even
    though the actual symbol type is relevant and therefore ignored.

    Commit bc7c9d620 ("efi/libstub/x86: Force 'hidden' visibility for
    extern declarations") made a change to the way external symbol
    references are classified, resulting in 'startup_32' now being
    emitted as a hidden symbol. This prevents the use of GOT entries to
    refer to this symbol via its absolute address, which recent toolchains
    (including Clang based ones) already avoid by default, making this
    change a no-op in the majority of cases.

    However, as it turns out, the LLVM linker classifies such hidden
    symbols as symbols with static linkage in fully linked ELF binaries,
    causing tools such as NM to output a lowercase 't' rather than an upper
    case 'T' for the type of such symbols. Since our sed expression only
    matches upper case letters for the symbol type, the line describing
    startup_32 is disregarded, resulting in a build error like the following

    arch/x86/boot/header.S:568:18: error: symbol 'ZO_startup_32' can not be
    undefined in a subtraction expression
    init_size: .long (0x00000000008fd000 - ZO_startup_32 +
    (((0x0000000001f6361c + ((0x0000000001f6361c >> 8) + 65536)
    - 0x00000000008c32e5) + 4095) & ~4095)) # kernel initialization size

    Given that we are only interested in the value of the symbol, let's match
    any character in the set 'a-zA-Z' instead.

    Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Tested-by: Nathan Chancellor <natechancellor@gmail.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/boot/Makefile | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
    index 95410d6ee2ff8..748b6d28a91de 100644
    --- a/arch/x86/boot/Makefile
    +++ b/arch/x86/boot/Makefile
    @@ -88,7 +88,7 @@ $(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE

    SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))

    -sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|z_.*\)$$/\#define ZO_\2 0x\1/p'
    +sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|z_.*\)$$/\#define ZO_\2 0x\1/p'

    quiet_cmd_zoffset = ZOFFSET $@
    cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
    --
    2.20.1
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