https://maskray.me/blog/2022-01-16-archives-and-start-lib
For every definition in an extracted archive member, we intern the symbol twice,
once for the archive index entry, once for the .o symbol table after extraction.
This is inefficient.
Symbols in a --start-lib ObjFile/BitcodeFile are only interned once because the
result is cached in symbols[i].
Just handle an archive using the --start-lib code path. We can therefore remove
ArchiveFile and LazyArchive. For many projects, archive member extraction ratio
is high and it is a net performance win. Linking a Release build of clang is
1.01x as fast.
Note: --start-lib scans symbols in the same order that llvm-ar adds them to the
index, so in the common case the semantics should be identical. If the archive
symbol table was created in a different order, or is incomplete, this strategy
may have different semantics. Such cases are considered user error.
The `is neither ET_REL nor LLVM bitcode` error is changed to a warning.
Previously an archive may have such members without a diagnostic. Using a
warning prevents breakage.
* For some tests, the diagnostics get improved where we did not consider
the archive member name: `b.a:` => `b.a(b.o):`.
* `no-obj.s`: the link is now allowed, matching GNU ld
* `archive-no-index.s`: the `is neither ET_REL nor LLVM bitcode` diagnostic is
demoted to a warning.
* `incompatible.s`: even when an archive is unextracted, we may report an
"incompatible with" error.
---
I recently decreased sizeof(SymbolUnion) by 8 and decreased memory usage quite a
bit, so retaining `symbols` for un-extracted archive members should not cause a
memory usage problem.
Reviewed By: peter.smith
Differential Revision: https://reviews.llvm.org/D119074
Any OUTPUT_FORMAT in a linker script overrides the emulation passed on
the command line, so record the passed bfdname and use that in the error
message about incompatible input files.
This prevents confusing error messages. For example, if you explicitly
pass `-m elf_x86_64` to LLD but accidentally include a linker script
which sets `OUTPUT_FORMAT(elf32-i386)`, LLD would previously complain
about your input files being compatible with elf_x86_64, which isn't the
actual issue, and is confusing because the input files are in fact
x86-64 ELF files.
Interestingly enough, this also prevents a segfault! When we don't pass
`-m` and we have an object file which is incompatible with the
`OUTPUT_FORMAT` set by a linker script, the object file is checked for
compatibility before it's added to the objectFiles vector.
config->emulation, objectFiles, and sharedFiles will all be empty, so
we'll attempt to access bitcodeFiles[0], but bitcodeFiles is also empty,
so we'll segfault. This commit prevents the segfault by adding
OUTPUT_FORMAT as a possible source of machine configuration, and it also
adds an llvm_unreachable to diagnose similar issues in the future.
Differential Revision: https://reviews.llvm.org/D76109
Some lit tests that call llvm-ar use the 'r' flag. If the target archive
already exists and is in a corrupt state, this can cause the test to fail. We
have added 'rm -f' calls before the llvm-ar calls to increase the
robustness of the tests.
Differential revision: https://reviews.llvm.org/D49184
llvm-svn: 338705
We currently don't do a good job of diagnosing inputs that would require
dynamic relocations to be applied to read only segments.
I am about to improve lld in that area, but unfortunately we developed
tests that depend on the current behavior.
To make clear what is actually changing, this first patch just updates
tests to not depend on the current behavior. In most cases this just
means using a rw section instead of a ro one, but that unfortunately
changes many addresses.
llvm-svn: 268145
