linux-kernel - 5.19-rc1 x86 build failure

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Date:   Tue, 7 Jun 2022 15:19:36 +0300
From:   Joe Damato <jdamato@...tly.com>
To:     x86@...nel.org
Cc:     jpoimboe@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, jiangshanlai@...il.com, bp@...e.de,
        brgerst@...il.com, Andrew.Cooper3@...rix.com
Subject: 5.19-rc1 x86 build failure

Greetings:

My apologies if this is the incorrect place to report this, but I got a
build error when trying to compile the net-next 5.19-rc1 tree.

git bisect says that commit a1e2c031ec394 ("x86/mm: Simplify
RESERVE_BRK()") is responsible for the build issue I am hitting.

I am performing this build on an x86_64 system with GNU C11 (Ubuntu
5.4.0-6ubuntu1~16.04.12) version 5.4.0 20160609 (x86_64-linux-gnu).

The assembler outputs a cryptic error message:

/tmp/ccnGOKZ5.s: Assembler messages:
/tmp/ccnGOKZ5.s:98: Error: missing ')'
/tmp/ccnGOKZ5.s:98: Error: missing ')'
/tmp/ccnGOKZ5.s:98: Error: missing ')'
/tmp/ccnGOKZ5.s:98: Error: junk at end of line, first unrecognized
character is `U'
/tmp/ccnGOKZ5.s:99: Error: missing ')'
/tmp/ccnGOKZ5.s:99: Error: missing ')'
/tmp/ccnGOKZ5.s:99: Error: missing ')'
/tmp/ccnGOKZ5.s:99: Error: junk at end of line, first unrecognized
character is `U'

I've asked GCC to generate the assembly and output so I can see more
specifically where this issue is (via "-fverbose-asm -Wa,-adhln=output"):

  96                            .pushsection .brk_reservation,"aw",@nobits
  97                            .brk.early_pgt_alloc:
  98 ???? 00000000              .skip ((2 * 3) * ((1UL) << 12))
****  Error: missing ')'
****  Error: missing ')'
****  Error: missing ')'
****  Error: junk at end of line, first unrecognized character is `U'
  98      0000
 100                            .popsection

This comes from arch/x86/mm/init.c, which has the following code:

RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE);

wherein INIT_PGT_BUF_SIZE (via PAGE_SIZE) has a "1UL" which makes the
assembler unhappy.

I don't really know what the correct way to fix this is; it seems that the
macro _AC should handle this if ASSEMBLY is defined, IIUC, but that does
not seem to be the case at this point in init.c.

Perhaps I am doing something incorrect during the build process causing
this to happen?

Thanks,
Joe