On Mon, Jun 22, 2020 at 07:56:39PM +0000, Nathan Chancellor wrote:
From: Ard Biesheuvel <ardb@xxxxxxxxxx>
commit bc310baf2ba381c648983c7f4748327f17324562 upstream.
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@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
---
Hi all,
Please apply this patch to 5.4 (and older releases if you feel it
necessary), as it fixes a build error that I see when linking with
ld.lld on certain distribution configurations after upstream commit
5214028dd89e ("x86/boot: Correct relocation destination on old linkers")
was applied in 5.4.48.
$ make -skj"$(nproc)" CC=clang LD=ld.lld O=out/x86_64 olddefconfig bzImage
...
ld.lld: error: undefined symbol: ZO__end
referenced by arch/x86/boot/header.o:(.header+0x71)
...
While the commit message references bc7c9d620 as the first problematic
commit, I see the same behavior of capital versus lowercase letters from
nm here too. I assume this is not seen in mainline because this commit
was already in the tree when 5214028dd89e was applied.
I've queued this for 5.4-4.9, thanks!
--
Thanks,
Sasha
