* `RelocationBaseSection::addReloc` increases `numRelativeRelocs`, which
duplicates the work done by RelocationSection<ELFT>::writeTo.
* --pack-dyn-relocs=android has inappropropriate DT_RELACOUNT.
AndroidPackedRelocationSection does not necessarily place relative relocations
in the front and DT_RELACOUNT might cause semantics error (though our
implementation doesn't and Android bionic doesn't use DT_RELACOUNT anyway.)
Move `llvm::partition` to a new function `partitionRels` and compute
`numRelativeRelocs` there. Now `RelocationBaseSection::addReloc` is trivial and
can be moved to the header to enable inlining.
The rest of DynamicReloc and `-z combreloc` handling is moved to the
non-template `RelocationBaseSection::computeRels` to decrease code size. My
x86-64 lld executable is 44+KiB smaller.
While here, rename `sort` to `combreloc`.
See http://lists.llvm.org/pipermail/llvm-dev/2020-April/140549.html
For the record, GNU ld changed to 64k max page size in 2014
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=7572ca8989ead4c3425a1500bc241eaaeffa2c89
"[RFC] ld/ARM: Increase maximum page size to 64kB"
Android driver forced 4k page size in AArch64 (D55029) and ARM (D77746).
A binary linked with max-page-size=4096 does not run on a system with a
higher page size configured. There are some systems out there that do
this and it leads to the binary getting `Killed!` by the kernel.
In the non-linker-script cases, when linked with -z noseparate-code
(default), the max-page-size increase should not cause any size
difference. There may be some VMA usage differences, though.
Reviewed By: psmith, MaskRay
Differential Revision: https://reviews.llvm.org/D77330
Port the D64906 technique to ARM. It deletes 3 alignments at
PT_LOAD boundaries for the default case: the size of an arm binary
decreases by at most 12kb.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D66749
llvm-svn: 370049
This fixed a bug in r369488. When config->isRela is false, i->r_addend
is not initialized (see encodeDynamicReloc). So we should check
config->isRela before accessing r_addend:
- if (j - i < 3 || i->r_addend)
+ if (j - i < 3 || (config->isRela && i->r_addend != 0))
Original description:
Currently, with Android dynamic relocation packing, only relative
relocations are grouped together. This patch implements similar
packing for non-relative relocations.
The implementation groups non-relative relocations with the same
r_info and r_addend, if using RELA. By requiring a minimum group
size of 3, this achieves smaller relocation sections. Building Android
for an ARM32 device, I see the total size of /system/lib decrease by
392 KB.
Grouping by r_info also allows the runtime dynamic linker to implement
an 1-entry cache to reduce the number of symbol lookup required. With
such 1-entry cache implemented on Android, I'm seeing 10% to 20%
reduction in total time spent in runtime linker for several executables
that I tested.
As a simple correctness check, I've also built x86_64 Android and booted
successfully.
Differential Revision: https://reviews.llvm.org/D65242
Patch by Vic Yang
llvm-svn: 369507
Currently, with Android dynamic relocation packing, only relative
relocations are grouped together. This patch implements similar
packing for non-relative relocations.
The implementation groups non-relative relocations with the same
r_info and r_addend, if using RELA. By requiring a minimum group
size of 3, this achieves smaller relocation sections. Building Android
for an ARM32 device, I see the total size of /system/lib decrease by
392 KB.
Grouping by r_info also allows the runtime dynamic linker to implement
an 1-entry cache to reduce the number of symbol lookup required. With
such 1-entry cache implemented on Android, I'm seeing 10% to 20%
reduction in total time spent in runtime linker for several executables
that I tested.
As a simple correctness check, I've also built x86_64 Android and booted
successfully.
Differential Revision: https://reviews.llvm.org/D66491
Patch by Vic Yang!
llvm-svn: 369488
Ported the D64906 technique to AArch64. It deletes 3 alignments at
PT_LOAD boundaries for the default case: the size of an aarch64 binary
decreases by at most 192kb.
If `sh_addralign(.tdata) < sh_addralign(.tbss)`,
we can potentially make `p_vaddr(PT_TLS)%p_align(PT_TLS) != 0`.
ld.so that are known to have problems if p_vaddr%p_align!=0:
* musl<=1.1.22
* FreeBSD 13.0-CURRENT (and before) rtld-elf arm64
New test aarch64-tls-vaddr-align.s checks that our workaround makes p_vaddr%p_align = 0.
Reviewed By: ruiu
Differential Revision: https://reviews.llvm.org/D64930
llvm-svn: 369344
Also change some options that have different semantics (cause confusion) in llvm-readelf mode:
-s => -S
-t => --symbols
-sd => --section-data
llvm-svn: 359651
Old: PT_LOAD(.data | PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .bss)
New: PT_LOAD(PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .data .bss)
The placement of | indicates page alignment caused by PT_GNU_RELRO. The
new layout has simpler rules and saves space for many cases.
Old size: roundup(.data) + roundup(.data.rel.ro)
New size: roundup(.data.rel.ro + .bss.rel.ro) + .data
Other advantages:
* At runtime the 3 memory mappings decrease to 2.
* start(PT_TLS) = start(PT_GNU_RELRO) = start(RW PT_LOAD). This
simplifies binary manipulation tools.
GNU strip before 2.31 discards PT_GNU_RELRO if its
address is not equal to the start of its associated PT_LOAD.
This has been fixed by https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f2731e0c374e5323ce4cdae2bcc7b7fe22da1a6f
But with this change, we will be compatible with GNU strip before 2.31
* Before, .got.plt (non-relro by default) was placed before .got (relro
by default), which made it impossible to have _GLOBAL_OFFSET_TABLE_
(start of .got.plt on x86-64) equal to the end of .got (R_GOT*_FROM_END)
(https://bugs.llvm.org/show_bug.cgi?id=36555). With the new ordering, we
can improve on this regard if we'd like to.
Reviewers: ruiu, espindola, pcc
Subscribers: emaste, arichardson, llvm-commits, joerg, jdoerfert
Differential Revision: https://reviews.llvm.org/D56828
llvm-svn: 356117
Patch by Rahul Chaudhry!
This change adds experimental support for SHT_RELR sections, proposed
here: https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
Pass '--pack-dyn-relocs=relr' to enable generation of SHT_RELR section
and DT_RELR, DT_RELRSZ, and DT_RELRENT dynamic tags.
Definitions for the new ELF section type and dynamic array tags, as well
as the encoding used in the new section are all under discussion and are
subject to change. Use with caution!
Pass '--use-android-relr-tags' with '--pack-dyn-relocs=relr' to use
SHT_ANDROID_RELR section type instead of SHT_RELR, as well as
DT_ANDROID_RELR* dynamic tags instead of DT_RELR*. The generated
section contents are identical.
'--pack-dyn-relocs=android+relr --use-android-relr-tags' enables both
'--pack-dyn-relocs=android' and '--pack-dyn-relocs=relr': lld will
encode the relative relocations in a SHT_ANDROID_RELR section, and pack
the rest of the dynamic relocations in a SHT_ANDROID_REL(A) section.
Differential Revision: https://reviews.llvm.org/D48247
llvm-svn: 336594
GNU linkers by convention supports both `--foo bar` and `--foo=bar` styles
for all long options that take arguments.
Differential Revision: https://reviews.llvm.org/D43972
llvm-svn: 326506
The Android relocation packing format is a more compact
format for dynamic relocations in executables and DSOs
that is based on delta encoding and SLEBs. An overview
of the format can be found in the Android source code:
https://android.googlesource.com/platform/bionic/+/refs/heads/master/tools/relocation_packer/src/delta_encoder.h
This patch implements relocation packing using that format.
This implementation uses a more intelligent algorithm for compressing
relative relocations than Android's own relocation packer. As a
result it can generally create smaller relocation sections than
that packer. If I link Chromium for Android targeting ARM32 I get a
.rel.dyn of size 174693 bytes, as compared to 371832 bytes with gold
and the Android packer.
Differential Revision: https://reviews.llvm.org/D39152
llvm-svn: 316775
Fangrui Song