-pie
--pic-executable
Create a position independent executable. This is currently only
supported on ELF platforms. Position independent executables are
similar to shared libraries in that they are relocated by the
dynamic linker to the virtual address the OS chooses for them
(which can vary between invocations). Like normal dynamically
linked executables they can be executed and symbols defined in the
executable cannot be overridden by shared libraries.
Differential revision: http://reviews.llvm.org/D18183
llvm-svn: 263693
-warn-common
Warn when a common symbol is combined with another common symbol
or with a symbol definition. Unix linkers allow this somewhat
sloppy practice, but linkers on some other operating systems do
not. This option allows you to find potential problems from
combining global symbols.
Differential revision: http://reviews.llvm.org/D17998
llvm-svn: 263413
error returned true if there was an error. This allows us to replace
the code like this
if (EC) {
error(EC, "something failed");
return;
}
with
if (error(EC, "something failed"))
return;
I thought that that was a good idea, but it turned out that we only
have two places to use this pattern. So this patch removes that feature.
llvm-svn: 263362
which was reverted because included
unrelative changes by mistake.
Original commit message:
[ELF] - Change all messages to lowercase to be consistent.
That is directly opposite to http://reviews.llvm.org/D18045,
which was reverted.
This patch changes all messages to start from lowercase letter if
they were not before.
That is done to be consistent with clang.
Differential revision: http://reviews.llvm.org/D18085
llvm-svn: 263337
This patch implements --build-id. After the linker creates an output file
in the memory buffer, it computes the FNV1 hash of the resulting file
and set the hash to the .note section as a build-id.
GNU ld and gold have the same feature, but their default choice of the
hash function is different. Their default is SHA1.
We made a deliberate choice to not use a secure hash function for the
sake of performance. Computing a secure hash is slow -- for example,
MD5 throughput is usually 400 MB/s or so. SHA1 is slower than that.
As a result, if you pass --build-id to gold, then the linker becomes about
10% slower than that without the option. We observed a similar degradation
in an experimental implementation of build-id for LLD. On the other hand,
we observed only 1-2% performance degradation with the FNV hash.
Since build-id is not for digital certificate or anything, we think that
a very small probability of collision is acceptable.
We considered using other signals such as using input file timestamps as
inputs to a secure hash function. But such signals would have an issue
with build reproducibility (if you build a binary from the same source
tree using the same toolchain, the build id should become the same.)
GNU linkers accepts --build-id=<style> option where style is one of
"MD5", "SHA1", or an arbitrary hex string. That option is out of scope
of this patch.
http://reviews.llvm.org/D18091
llvm-svn: 263292
That is directly opposite to http://reviews.llvm.org/D18045,
which was reverted.
This patch changes all messages to start from lowercase letter if
they were not before.
That is done to be consistent with clang.
Differential revision: http://reviews.llvm.org/D18085
llvm-svn: 263252
It was discussed to make all messages be
lowercase to be consistent with clang.
(also reverts the r263128 which fixed
build bot fail after r263125)
Original commit message:
[ELF] - Consistent spelling for error/warning messages
Previously error and warnings were not consistent in lld.
Some of them started from lowercase letter, others from
uppercase. Also there was one or two which had a dot at the end.
This patch changes all messages to start from uppercase letter if
they were not before.
Differential revision: http://reviews.llvm.org/D18045
llvm-svn: 263240
This patch adds --thread option and use parallel_for_each to write
sections in regular OutputSections.
This is the first patch to use more than one threads.
Note that --thread is off by default because it is experimental.
At this moment I still want to focus on single thread performance
because multi-threading is not a magic wand to fix performance
problems after all. It is generally very hard to make a slow program
faster by threads. Therefore, I want to make the linker as efficient
as possible first and then look for opportunity to make it even faster
using more than one core.
Here are some numbers to link programs with and without --threads
and using GNU gold. Numbers are in seconds.
Clang
w/o --threads 0.697
w --threads 0.528
gold 1.643
Scylla
w/o --threads 5.032
w --threads 4.935
gold 6.791
GNU gold
w/o --threads 0.550
w --threads 0.551
gold 0.737
I limited the number of cores these processes can use to 4 using
perf command, so although my machine has 20 physical cores, the
performance gain I observed should be reproducible with a machine
which is not as beefy as mine.
llvm-svn: 263190
It looks a bit wierd that we have to initialize symbols for all ELFT
types when we use only one ELFT for link. We can only init those
that we need. Patch fixes it.
Differential revision: http://reviews.llvm.org/D18047
llvm-svn: 263133
Previously error and warnings were not consistent in lld.
Some of them started from lowercase letter, others from
uppercase. Also there was one or two which had a dot at the end.
This patch changes all messages to start from uppercase letter if
they were not before.
Differential revision: http://reviews.llvm.org/D18045
llvm-svn: 263125
Summary:
They are needed for inline asm during LTO.
In particular we hit the report_fatal_error on
llvm/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp:138
LLVM ERROR: Inline asm not supported by this streamer because we don't have an asm parser for this target
Reviewers: ruiu, rafael
Subscribers: Bigcheese, llvm-commits, joker.eph
Differential Revision: http://reviews.llvm.org/D18027
llvm-svn: 263094
Summary:
This is useful for debugging issues with LTO.
The option follows the analogous option in ld64 and the gold plugin (per
Rafael's suggestion).
For starters, this only dumps the combined bitcode file.
In a future patch I will add dumping for the .o file.
The naming of the output follows ld64's convention which is slightly more
consistent IMO (consistent `.lto.<extension>` for all the files).
Reviewers: rafael, ruiu
Subscribers: joker.eph, Bigcheese, llvm-commits
Differential Revision: http://reviews.llvm.org/D18006
llvm-svn: 263055
It was causing errors like
/lib/libc.so.6 is incompatible with elf_x86_64
when linking on Fedora.
Every system has different default paths. It seems better to just trust
the driver to pass the correct -L options.
This reverts commit 262910.
llvm-svn: 262941
The variables corresponding to command line options are named mechanically.
Because the option for the variable is -noinhibit-exec and not -no-inhibit-exec,
it should be name this way.
llvm-svn: 262911
Now that DarwinLdDriver is the only derived class of Driver.
This patch merges them and actually removed the class because
they can now just be non-member functions. This change simplifies
a common header, Driver.h.
http://reviews.llvm.org/D17788
llvm-svn: 262502
This patch implements the same algorithm as LLD/COFF's ICF. I'm
not going to repeat the same description about how it works, so you
want to read the comment in ICF.cpp in this patch if you want to know
the details. This algorithm should be more powerful than the ICF
algorithm implemented in GNU gold. It can even merge mutually-recursive
functions (which is harder than one might think).
ICF is a fairly effective size optimization. Here are some examples.
LLD: 37.14 MB -> 35.80 MB (-3.6%)
Clang: 59.41 MB -> 57.80 MB (-2.7%)
The lacking feature is "safe" version of ICF. This merges all
identical sections. That is not compatible with a C/C++ language
requirement that two distinct functions must have distinct addresses.
But as long as your program do not rely on the pointer equality
(which is in many cases true), your program should work with the
feature. LLD works fine for example.
GNU gold implements so-called "safe ICF" that identifies functions
that are safe to merge by heuristics -- for example, gold thinks
that constructors are safe to merge because there is no way to
take an address of a constructor in C++. We have a different idea
which David Majnemer suggested that we add NOPs at beginning of
merged functions so that two or more pointers can have distinct
values. We can do whichever we want, but this patch does not
include neither.
http://reviews.llvm.org/D17529
llvm-svn: 261912
-r, -relocatable - Generate relocatable output
Currently does not have support for files containing
relocation sections with entries that refer to local
symbols (like rel[a].eh_frame which refer to sections
and not to symbols)
Differential revision: http://reviews.llvm.org/D14382
llvm-svn: 261838
This patch moves BitcodeFile instantiation into createObjectFile.
Previously, we handle bitcode files outside that function and did
not handle for --whole-archive.
http://reviews.llvm.org/D17527
llvm-svn: 261663
Previously, Target held a value until a new value is assigned to the
variable. That was a benign leak -- that was not an unbounded leak
and didn't grab any resources except a small amount of memory. But
it is better to fix than leaving as is.
llvm-svn: 260592
Previously, we had code for linker scripts in Writer. This patch
separates that as LinkerScript class. The class provides a few
functions to query linker scripts and is also a container of some
linker-script-specific information.
Hopefully, Writer will only implement the default behavior and let
the new class handle gotchas regarding linker scripts.
llvm-svn: 260591
