Stream: git-wasmtime

Topic: wasmtime / Issue #1055 encoding tables are non-shareable ...

Wasmtime GitHub notifications bot (Feb 03 2021 at 17:03):

bjorn3 commented on Issue #1055:

The new backend framework uses a completely different architecture that doesn't include encoding tables.

Wasmtime GitHub notifications bot (Feb 03 2021 at 17:28):

cfallin closed Issue #1055:

Looking at a recent-ish Firefox nightly, I see the following:

# Look at x86 cranelift symbols, sorted by (descending) size, in the .data.rel.ro section.
froydnj@hawkeye:~$ readelf -sW firefox/libxul.so|grep cranelift |sort -k 3 -g -r |awk '$7 == 27 { print }' |grep OBJECT |grep x86
123872: 0000000007342048  9480 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x8610enc_tables18RECIPE_CONSTRAINTS17h10c82bc0de555a21E
123849: 0000000007344550  3792 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x8610enc_tables12RECIPE_NAMES17h54e6a911fe6097bbE
123866: 0000000007345c20  1896 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x8610enc_tables17RECIPE_PREDICATES17hc3712077e222c860E
123908: 0000000007347da0   408 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x868settings11DESCRIPTORS17h03dfd2ae0adf323dE
123854: 0000000007346388   120 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x8610enc_tables15INST_PREDICATES17h3a3bab86e4a3b3e7E
123911: 0000000007347f38    96 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x868settings8TEMPLATE17hdfd5aa2b6a7f01ecE
123922: 0000000007341ea8    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers9GPR8_DATA17h4c7c028be6f5b4d8E
123921: 0000000007341f68    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers9FPR8_DATA17h4d3540abe0a3bbe2E
123920: 0000000007341e18    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers9FLAG_DATA17h06234297cfb01581E
123919: 0000000007341f38    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers9ABCD_DATA17h231c9e2f56f02113E
123918: 0000000007341db8    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers8GPR_DATA17h327360c70468dbffE
123917: 0000000007341de8    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers8FPR_DATA17h3d44028fd0ecbabdE
123915: 0000000007341f08    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers25GPR8_ZERO_DEREF_SAFE_DATA17h743615e457b73283E
123914: 0000000007341e78    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers24GPR_ZERO_DEREF_SAFE_DATA17h82d7795ce9382dfbE
123913: 0000000007341ed8    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers20GPR8_DEREF_SAFE_DATA17h460e84f7bb9ca949E
123912: 0000000007341e48    48 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers19GPR_DEREF_SAFE_DATA17had1b3296ef50e9ebE
123916: 0000000007341f98    32 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x869registers4INFO17h2a2b91216d7265ffE
123855: 0000000007345c00    32 OBJECT  LOCAL  DEFAULT   27 _ZN17cranelift_codegen3isa3x8610enc_tables16LEGALIZE_ACTIONS17h4ddebdf4d5a40777E

There's about 15k of symbols in cranelift_codegen::isa::x86 that live in .data.rel.ro, which renders them non-shareable. For Firefox's purposes, we'd really like to minimize the amount of data that lives in .data.rel.ro, moving it to .rodata if at all possible.

The usual problem for data winding up in .data.rel.ro is data structures that contain slices, and indeed, for RECIPE_CONSTRAINTS, the RecipeConstraints structure has a couple slices in it. I haven't looked at RECIPE_NAMES, RECIPE_PREDICATES, and so forth, but I assume the problems are similar there.

It would be great if things were shuffled around somehow so the data associated with these symbols could live in .rodata. unicode-rs/unicode-normalization#14 is one example of how we addressed this in another Rust library; I might have time to implement the same changes here, not sure though. We don't necessarily have to address all of these, but addressing the top five or so would make a big difference.

/cc @EricRahm

Last updated: Oct 23 2024 at 20:03 UTC