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[ELF] More dynamic relocation packing

Description

[ELF] More dynamic relocation packing

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!

Details

Committed
MaskRayAug 20 2019, 8:02 PM
Differential Revision
D66491: [COFF] Check errorCount before committing the output file
Parents
rL369487: libcxx: Rename .hpp files in libcxx/benchmarks to .h
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