From: Kevin Brodsky <kevin.brodsky@arm•com>
To: Ard Biesheuvel <ardb@kernel•org>,
Ard Biesheuvel <ardb+git@google•com>,
linux-arm-kernel@lists•infradead.org
Cc: linux-kernel@vger•kernel.org, Will Deacon <will@kernel•org>,
Catalin Marinas <catalin.marinas@arm•com>,
Mark Rutland <mark.rutland@arm•com>,
Ryan Roberts <ryan.roberts@arm•com>,
Anshuman Khandual <anshuman.khandual@arm•com>,
Liz Prucka <lizprucka@google•com>,
Seth Jenkins <sethjenkins@google•com>,
Kees Cook <kees@kernel•org>, Mike Rapoport <rppt@kernel•org>,
David Hildenbrand <david@kernel•org>,
Andrew Morton <akpm@linux-foundation•org>,
Jann Horn <jannh@google•com>,
linux-mm@kvack•org, linux-hardening@vger•kernel.org,
linuxppc-dev@lists•ozlabs.org, linux-sh@vger•kernel.org
Subject: Re: [PATCH v6 09/15] arm64: Move fixmap and kasan page tables to end of kernel image
Date: Mon, 1 Jun 2026 10:37:03 +0200 [thread overview]
Message-ID: <69488547-cf2a-4aa0-bca7-0cb65aa01914@arm.com> (raw)
In-Reply-To: <feab72b8-2961-4145-ac5c-80e820bf1ce9@app.fastmail.com>
On 29/05/2026 16:47, Ard Biesheuvel wrote:
>>>>> + /* fixmap BSS starts here - preceding data/BSS is omitted from the linear map */
>>>>> + .pgdir.bss (NOLOAD) : ALIGN(PAGE_SIZE) {
>>>> Do we actually need the NOLOAD type here?
>>> Yes, otherwise it is emitted as PROGBITS, resulting in all of BSS to be
>>> emitted into Image.
>> That's rather strange, aren't the .pgdir.bss input sections already
>> NOBITS since __pgtbl_bss is only used on default-initialised globals?
> Not sure why, but the section was PROGBITS not NOBITS before I added the (NOLOAD)
I've had a closer look into this. Similar sections in other
architectures are all named .bss..<something>. If I rename this section
to .bss..pgdir, then indeed the compiler does emit an object file with
that section marked NOBITS:
$ readelf -e out/arch/arm64/mm/fixmap.o | grep bss
[ 4] .bss NOBITS 0000000000000000 0002ac 000000
00 WA 0 0 1
[18] .bss..pgdir NOBITS 0000000000000000 000750 005000
00 WA 0 0 4096
And then the linker does the right thing without having to use NOLOAD.
I was concerned that .bss..pgdir might get caught by BSS_SECTION(), but
it seems that the double dots are meant to prevent exactly that.
- Kevin
next prev parent reply other threads:[~2026-06-01 8:37 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-26 17:58 [PATCH v6 00/15] arm64: Unmap linear alias of kernel data/bss Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 01/15] arm64: mm: Remove bogus stop condition from map_mem() loop Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 02/15] arm64: mm: Drop redundant pgd_t* argument from map_mem() Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 03/15] arm64: mm: Check for pud_/pmd_set_huge() failures on kernel mappings Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 04/15] arm64: mm: Preserve existing table mappings when mapping DRAM Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 05/15] arm64: mm: Preserve non-contiguous descriptors " Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 06/15] arm64: mm: Permit contiguous descriptors to be manipulated Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 07/15] arm64: kfence: Avoid NOMAP tricks when mapping the early pool Ard Biesheuvel
2026-05-29 8:25 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 08/15] arm64: mm: Permit contiguous attribute for preliminary mappings Ard Biesheuvel
2026-05-29 8:25 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 09/15] arm64: Move fixmap and kasan page tables to end of kernel image Ard Biesheuvel
2026-05-29 8:27 ` Kevin Brodsky
2026-05-29 11:19 ` Ard Biesheuvel
2026-05-29 14:42 ` Kevin Brodsky
2026-05-29 14:47 ` Ard Biesheuvel
2026-06-01 8:37 ` Kevin Brodsky [this message]
2026-06-01 8:39 ` Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 10/15] arm64: mm: Don't abuse memblock NOMAP to check for overlaps Ard Biesheuvel
2026-05-29 8:28 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 11/15] arm64: mm: Map the kernel data/bss read-only in the linear map Ard Biesheuvel
2026-05-29 8:28 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 12/15] powerpc/code-patching: Avoid r/w mapping of the zero page Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 13/15] sh: cast away constness from the zero page when flushing it from the cache Ard Biesheuvel
2026-05-27 9:31 ` Geert Uytterhoeven
2026-05-28 5:46 ` Mike Rapoport
2026-05-28 6:14 ` Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 14/15] mm: Make empty_zero_page[] const Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 15/15] arm64: mm: Unmap kernel data/bss entirely from the linear map Ard Biesheuvel
2026-05-29 8:29 ` Kevin Brodsky
2026-05-29 8:34 ` Ard Biesheuvel
2026-05-29 8:49 ` Kevin Brodsky
2026-05-29 11:48 ` Ard Biesheuvel
2026-05-29 8:31 ` [PATCH v6 00/15] arm64: Unmap linear alias of kernel data/bss Kevin Brodsky
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