This is not a linker feature, but in order to learn how Mach-O
executables are constructed, I'll implement a dump feature.
I'll remove the feature once I understand the structure of Mach-O
binaries.
Previously, we created dynamic relocations against read-only sections
if the sections contain relocations against weak undefined symbols.
Since such dynamic relocations cannot be applied at load-time, the
generated executables failed with SEGV.
Now, such relocations are resolved to address 0.
Reported at https://github.com/rui314/mold/pull/110
Linking clang-13 with debug info takes ~3.6 seconds on a simulated
10-core/20-threads machine. mold spends most of its time (~2.3 seconds)
merging string literals in .debug_str. Input .debug_str sections contain
70 million string literals in total, which is reduced to 2 million after
de-duplication. The input object files contain a lot of duplicates.
clang-13 with debug info is enormous -- it is ~3.1 GiB after linking.
It looks like TBB's concurrent hashmap doesn't scale well with the
input.
In this patch, I implemented our own concurrent hashmap. The hashmap
is extremely lightweight and support only the key-value insertion
operation. It doesn't even support rehashing. It aborts once the hash
table becomes full.
In order to know the correct size for the hashmap before inserting
strings into it, I also implemented HyperLogLog algorithm in this patch.
HyperLogLog is an algorithm that gives a fairly accurate estimate on
the number of unique elements.
With this patch, mold can link clang-13 in ~2.5 seconds, which is ~30%
faster than before.
https://github.com/rui314/mold/issues/73
Previously, if a weak undefined symbol cannot be resolved within
an output of the linker, mold turned it into an absolute symbol
with value 0. However, other linkers export such symbols as a
weak dynamic symbol, so that the symbol gets another chance to be
resolved at runtime.
This patch implements the behavior.
This is needed by Gentoo's dev-libs/nsync-1.20.1 package.
Previously, we turned unresolved undefined symbols into dynamic
symbols. This patch changed the behavior so that such symbols
are turned into non-dynamic absolute symbols with value zero.
This change is needed by Gentoo's dev-libs/wayland-protocols-1.21
package.
The configure script in Gentoo's dev-libs/jansson-2.13.1-r1 package
treats mold 0.1.1 as GNU ld 0.1.1, which is from 1980s if existed.
Adding "GNU gold" to the help message solves the nasty issue, as the
configure script considers any version of GNU gold supports modern
features.
