Re: [PATCH v9 0/6] add support for relative references in special sections
* Ard Biesheuvel wrote: > On 27 June 2018 at 17:15, Will Deacon wrote: > > Hi Ard, > > > > On Tue, Jun 26, 2018 at 08:27:55PM +0200, Ard Biesheuvel wrote: > >> This adds support for emitting special sections such as initcall arrays, > >> PCI fixups and tracepoints as relative references rather than absolute > >> references. This reduces the size by 50% on 64-bit architectures, but > >> more importantly, it removes the need for carrying relocation metadata > >> for these sections in relocatable kernels (e.g., for KASLR) that needs > >> to be fixed up at boot time. On arm64, this reduces the vmlinux footprint > >> of such a reference by 8x (8 byte absolute reference + 24 byte RELA entry > >> vs 4 byte relative reference) > >> > >> Patch #3 was sent out before as a single patch. This series supersedes > >> the previous submission. This version makes relative ksymtab entries > >> dependent on the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS rather > >> than trying to infer from kbuild test robot replies for which architectures > >> it should be blacklisted. > >> > >> Patch #1 introduces the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS, > >> and sets it for the main architectures that are expected to benefit the > >> most from this feature, i.e., 64-bit architectures or ones that use > >> runtime relocations. > >> > >> Patch #2 add support for #define'ing __DISABLE_EXPORTS to get rid of > >> ksymtab/kcrctab sections in decompressor and EFI stub objects when > >> rebuilding existing C files to run in a different context. > > > > I had a small question on patch 3, but it's really for my understanding. > > So, for patches 1-3: > > > > Reviewed-by: Will Deacon > > > > Thanks all. > > Thomas, Ingo, > > Except for the below tweak against patch #3 for powerpc, which may > apparently get confused by an input section called .discard without > any suffixes, this series is good to go, but requires your ack to > proceed, so I would like to ask you to share your comments and/or > objections. Also, any suggestions or recommendations regarding the > route these patches should take are highly appreciated. LGTM: Acked-by: Ingo Molnar Regarding route - I suspect -mm would be good, or any other tree that does a lot of cross-arch testing? Thanks, Ingo
Re: [PATCH v9 0/6] add support for relative references in special sections
On 27 June 2018 at 17:15, Will Deacon wrote:
> Hi Ard,
>
> On Tue, Jun 26, 2018 at 08:27:55PM +0200, Ard Biesheuvel wrote:
>> This adds support for emitting special sections such as initcall arrays,
>> PCI fixups and tracepoints as relative references rather than absolute
>> references. This reduces the size by 50% on 64-bit architectures, but
>> more importantly, it removes the need for carrying relocation metadata
>> for these sections in relocatable kernels (e.g., for KASLR) that needs
>> to be fixed up at boot time. On arm64, this reduces the vmlinux footprint
>> of such a reference by 8x (8 byte absolute reference + 24 byte RELA entry
>> vs 4 byte relative reference)
>>
>> Patch #3 was sent out before as a single patch. This series supersedes
>> the previous submission. This version makes relative ksymtab entries
>> dependent on the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS rather
>> than trying to infer from kbuild test robot replies for which architectures
>> it should be blacklisted.
>>
>> Patch #1 introduces the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS,
>> and sets it for the main architectures that are expected to benefit the
>> most from this feature, i.e., 64-bit architectures or ones that use
>> runtime relocations.
>>
>> Patch #2 add support for #define'ing __DISABLE_EXPORTS to get rid of
>> ksymtab/kcrctab sections in decompressor and EFI stub objects when
>> rebuilding existing C files to run in a different context.
>
> I had a small question on patch 3, but it's really for my understanding.
> So, for patches 1-3:
>
> Reviewed-by: Will Deacon
>
Thanks all.
Thomas, Ingo,
Except for the below tweak against patch #3 for powerpc, which may
apparently get confused by an input section called .discard without
any suffixes, this series is good to go, but requires your ack to
proceed, so I would like to ask you to share your comments and/or
objections. Also, any suggestions or recommendations regarding the
route these patches should take are highly appreciated.
Ard.
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 2d9c63f41031..61c844d4ab48 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -287,7 +287,7 @@ unsigned long read_word_at_a_time(const void *addr)
* visible to the compiler.
*/
#define __ADDRESSABLE(sym) \
- static void * __attribute__((section(".discard"), used))\
+ static void * __attribute__((section(".discard.addressable"), used)) \
__PASTE(__addressable_##sym, __LINE__) = (void *)
/**
Re: [PATCH v9 0/6] add support for relative references in special sections
Hi Ard, On Tue, Jun 26, 2018 at 08:27:55PM +0200, Ard Biesheuvel wrote: > This adds support for emitting special sections such as initcall arrays, > PCI fixups and tracepoints as relative references rather than absolute > references. This reduces the size by 50% on 64-bit architectures, but > more importantly, it removes the need for carrying relocation metadata > for these sections in relocatable kernels (e.g., for KASLR) that needs > to be fixed up at boot time. On arm64, this reduces the vmlinux footprint > of such a reference by 8x (8 byte absolute reference + 24 byte RELA entry > vs 4 byte relative reference) > > Patch #3 was sent out before as a single patch. This series supersedes > the previous submission. This version makes relative ksymtab entries > dependent on the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS rather > than trying to infer from kbuild test robot replies for which architectures > it should be blacklisted. > > Patch #1 introduces the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS, > and sets it for the main architectures that are expected to benefit the > most from this feature, i.e., 64-bit architectures or ones that use > runtime relocations. > > Patch #2 add support for #define'ing __DISABLE_EXPORTS to get rid of > ksymtab/kcrctab sections in decompressor and EFI stub objects when > rebuilding existing C files to run in a different context. I had a small question on patch 3, but it's really for my understanding. So, for patches 1-3: Reviewed-by: Will Deacon Thanks, Will
Re: [PATCH v9 0/6] add support for relative references in special sections
Ard Biesheuvel writes: > This adds support for emitting special sections such as initcall arrays, > PCI fixups and tracepoints as relative references rather than absolute > references. This reduces the size by 50% on 64-bit architectures, but > more importantly, it removes the need for carrying relocation metadata > for these sections in relocatable kernels (e.g., for KASLR) that needs > to be fixed up at boot time. On arm64, this reduces the vmlinux footprint > of such a reference by 8x (8 byte absolute reference + 24 byte RELA entry > vs 4 byte relative reference) ... > > Cc: Arnd Bergmann > Cc: Kees Cook > Cc: Will Deacon > Cc: Michael Ellerman This seems to be working on powerpc. It boots on a couple of machines with no obvious badness. And there's some size reduction with a random config I had lying around: Total: Before=14820494, After=14673313, chg -0.99% It can get some more testing once it's in linux-next as far as I'm concerned. Acked-by: Michael Ellerman (powerpc) cheers
[PATCH v9 0/6] add support for relative references in special sections
This adds support for emitting special sections such as initcall arrays, PCI fixups and tracepoints as relative references rather than absolute references. This reduces the size by 50% on 64-bit architectures, but more importantly, it removes the need for carrying relocation metadata for these sections in relocatable kernels (e.g., for KASLR) that needs to be fixed up at boot time. On arm64, this reduces the vmlinux footprint of such a reference by 8x (8 byte absolute reference + 24 byte RELA entry vs 4 byte relative reference) Patch #3 was sent out before as a single patch. This series supersedes the previous submission. This version makes relative ksymtab entries dependent on the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS rather than trying to infer from kbuild test robot replies for which architectures it should be blacklisted. Patch #1 introduces the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS, and sets it for the main architectures that are expected to benefit the most from this feature, i.e., 64-bit architectures or ones that use runtime relocations. Patch #2 add support for #define'ing __DISABLE_EXPORTS to get rid of ksymtab/kcrctab sections in decompressor and EFI stub objects when rebuilding existing C files to run in a different context. Patches #4 - #6 implement relative references for initcalls, PCI fixups and tracepoints, respectively, all of which produce sections with order ~1000 entries on an arm64 defconfig kernel with tracing enabled. This means we save about 28 KB of vmlinux space for each of these patches. [From the v7 series blurb, which included the jump_label patches as well]: For the arm64 kernel, all patches combined reduce the memory footprint of vmlinux by about 1.3 MB (using a config copied from Ubuntu that has KASLR enabled), of which ~1 MB is the size reduction of the RELA section in .init, and the remaining 300 KB is reduction of .text/.data. Branch: git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git relative-special-sections-v9 Changes since v8: - add Nico's ack (#2) - drop 'const' qualifier from __ADDRESSABLE(sym) to prevent mismatching attributes for the .discard section (#3) - drop all uses of VMLINUX_SYMBOL_STR(), which is on its way out (#3 - #6) Changes since v7: - dropped the jump_label patches, these will be revisited in a separate series - reorder __DISABLE_EXPORTS with __KSYM_DEPS__ check in #2 - use offset_to_ptr() helper function to abstract the relative pointer conversion [int *off -> (ulong)off + *off] (#3 - #6) - rebase onto v4.16-rc3 Changes since v6: - drop S390 from patch #1 introducing HAVE_ARCH_PREL32_RELOCATIONS: kbuild robot threw me some s390 curveballs, and given that s390 does not define CONFIG_RELOCATABLE in the first place, it does not benefit as much from relative references as arm64, x86 and power do - add patch to allow symbol exports to be disabled at compilation unit granularity (#2) - get rid of arm64 vmlinux.lds.S hunk to ensure code generated by __ADDRESSABLE gets discarded from the EFI stub - it is no longer needed after adding #2 (#1) - change _ADDRESSABLE() to emit a data reference, not a code reference - this is another simplification made possible by patch #2 (#3) - add Steven's ack to #6 - split x86 jump_label patch into two (#9, #10) Changes since v5: - add missing jump_label prototypes to s390 jump_label.h (#6) - fix inverted condition in call to jump_entry_is_module_init() (#6) Changes since v4: - add patches to convert x86 and arm64 to use relative references for jump tables (#6 - #8) - rename PCI patch and add Bjorn's ack (#4) - rebase onto v4.15-rc5 Changes since v3: - fix module unload issue in patch #5 reported by Jessica, by reusing the updated routine for_each_tracepoint_range() for the quiescent check at module unload time; this requires this routine to be moved before tracepoint_module_going() in kernel/tracepoint.c - add Jessica's ack to #2 - rebase onto v4.14-rc1 Changes since v2: - Revert my slightly misguided attempt to appease checkpatch, which resulted in needless churn and worse code. This v3 is based on v1 with a few tweaks that were actually reasonable checkpatch warnings: unnecessary braces (as pointed out by Ingo) and other minor whitespace misdemeanors. Changes since v1: - Remove checkpatch errors to the extent feasible: in some cases, this involves moving extern declarations into C files, and switching to struct definitions rather than typedefs. Some errors are impossible to fix: please find the remaining ones after the diffstat. - Used 'int' instead if 'signed int' for the various offset fields: there is no ambiguity between architectures regarding its signedness (unlike 'char') - Refactor the different patches to be more uniform in the way they define the section entry type and accessors in the .h file, and avoid the need to add #ifdefs to the C code. Cc: Arnd Bergmann Cc: Kees Cook Cc: Will Deacon Cc: Michael Ellerman
