This option reverse input sections before assigning offsets to them.
This is useful to detect an unintended dependency between static
initializers in different translation units. C++ only guarantees that
static initializers are invoked from top to bottom in a single
translation unit, and it doesn't guaratee anything about the order of
initialization between translation units.
By (partially) reversing the contents of .init_array using
--reverse-sections, you can run your program with a completely
reversed initialization order.
This commit ensure that all symbol resolution results are cleared
after LTO, so that the following second symbol resolution will not
be affected by the previous results.
This patch removes the --shuffle-sections option that takes an
argument as I'm still thinking about a better name for the option.
You can still use `--shuffle-sections` that doesn't take an argument.
If a relocation's r_sym value is 0 (i.e. it refers the undefined symbol
at the beginning of the symbol table), it has to handled as if S were 0.
We used to handle as if S were -1.
In addition to that, even if a relocation needs a dynamic base relocation,
it doesn't mean its expression is always S+A. For example, calling an
absolute address needs a dynamic relocation but its expression is S+A-P.
Fixes https://github.com/rui314/mold/issues/348
This reverts commit ddcb7b4197. `is_dso`
is used by hot functions such as `Symbol::get_addr()`, so we want to
eliminate the cost of virtual function dispatch.
Since compiled IR objects may contain mergeable string sections, we
don't know the estimated number of items in output mergeable sections.
Previously, we created the concurrent hash tables for output mergeable
sections before compiling IR objects, so there was a chance to see
the "concurrent hash table full" error.
This commit moves the code to add section pieces to output mergeable
sections after `do_lto`.
If the --shuffle-sections is given, mold now randomize the output by
shuffling input sections randomly. This feature is compatible with lld's
--shuffle-sections=SEED option introduced in
https://reviews.llvm.org/D74791.
This feature is useful when you want to equalize the conditions of
benchmarks. That is, some particular memory layout can produce a very
good benchmark number due to hardware-level cache hit rate or something
like that. Therefore, even if you get a good benchmark number after
changing code, there's a chance that that's caused by the layout change
and not by the new code itself. With --shuffle-sections, you can isolate
that.
The other use case I can think of is to enhance security. If you build
your program as a position-independent executable, the kernel
automatically enables ASLR (Address Space Layout Randomization), but ASLR
only shift the entire program image in memory by some random offset;
Relative offsets between sections remain the same. If you compile programs
from source, by using --shuffle-sections, you can make the offsets
unpredictable to attackers.
The LTO plugin API support is still in progress, but with this change,
mold can link itself with `-flto` with both GCC and Clang.
Since mold now supports LTO natively, I removed the fallback mechanism
to ld.bfd or ld.lld that I implemented in
a5029d19a8.
Fixes https://github.com/rui314/mold/issues/181
Prefer pure virtual 'mold:🧝:InputFile::is_dso()' (actually
implemented in 'mold:🧝:ObjectFile' and 'mold:🧝:SharedFile')
over the field of the same name, adjust related code.
Signed-off-by: Dmitry Antipov dantipov@cloudlinux.com
Currently, the sections we create for copy relocations are named .dynbss
and .dynbss.rel.ro. Section names shouldn't be significant in ELF
executables, so we should be able to name them as we want.
However, in practice, valgrind treat a section with the name .dynbss
in a special way and crashes if an executable contains both .bss and
.dynbss due to the following assertion failure:
$ valgrind ./prog
==1960252== Memcheck, a memory error detector
==1960252== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1960252== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==1960252== Command: ./prog
==1960252==
valgrind: m_debuginfo/readelf.c:2271 (vgModuleLocal_read_elf_debug_info): Assertion 'di->bss_svma + di->bss_size == svma' failed.
Segmentation fault (core dumped)
This commit is a workaround for the valgrind issue. We simply rename
dynbss and .dynbss.rel.ro to .copyrel and .copyrel.rel.ro, respectively.
Fixes https://github.com/rui314/mold/issues/159
Ensure that all xxhash functions are inlined. Since it eliminates
external dependencies, we no longer have to link against libxxhash.a
or libxxhash.so at all.
`SYSTEM_XXHASH` Makefile variable has been removed because it is
no longer relevant.
This is a mold-only experimental feature. If the flag is given,
mold prints out dependencies between input files as tab-separated
tuples of (`source-file`, `dest-file`, `symbol`). Each line of the
output means `source-file` depends on `dest-file` to use `symbol`.
With the dependency information, you can analyze for example why
some archive file member is included in a linker's output.
You can also for example know what symbols have to be removed
to eliminate the dependency to some shared library file.
I'm not sure if I'll include this flag in the next release or
document this feature, but it looks promising so far. If you like
or dislike this feature, please leave a comment on GitHub.
This is an example of the output when linking mold with mold:
https://gist.github.com/rui314/e1d70bbdebfabb881be7167314b58f48
This commit adds the `--emit-relocs` option to mold. If the flag is
given, mold copies relocation sections from input files to an output
file. This option is used by some binary post-processing tools such
as Facebook's Bolt.
It looks like the relocations emitted by `--emit-relocs` are correct,
but I didn't do extensive testing. If you find any problem, please
let me know.
Fixes https://github.com/rui314/mold/issues/177
Previously, we always uncompress compressed debug sections to
in-memory buffer before copying them to the final output buffer.
This patch eliminates that redundant copy whenever possible.
`--repro` is a hidden command flag for debugging.
Previously, if the flag was given, mold would create a `.repro`
section in an output file with all input files as its contents.
The flaw of the design is that when mold fails to create an output
file, no .repro section would be created.
So I changed the behavior in this commit. Now, the tar file is
created as an independent file.
Add 'mold:🧝:GlobPattern::Element' and 'mold::macho::SplitInfo'
trivial constructors to fix all '-Wmissing-field-initializers' as
reported both by g++ and clang++.
Signed-off-by: Dmitry Antipov <dantipov@cloudlinux.com>
