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Rui Ueyama 634ddf0bec ELF: Implement --build-id. 
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
 		2016-03-11 20:51:53 +00:00
..
COFF Merge DarwinLdDriver and Driver. 2016-03-02 19:08:05 +00:00
ELF ELF: Implement --build-id. 2016-03-11 20:51:53 +00:00
cmake/modules
…
docs Delete more ELF bits from the old linker. 2016-02-28 16:03:37 +00:00
include/lld Merge DarwinLdDriver and Driver. 2016-03-02 19:08:05 +00:00
lib Simplify string operations. NFC. 2016-03-03 00:51:23 +00:00
test ELF: Implement --build-id. 2016-03-11 20:51:53 +00:00
tools/lld Inline a trivial CMakeLists.txt. 2016-03-03 01:56:23 +00:00
unittests Merge DarwinLdDriver and Driver. 2016-03-02 19:08:05 +00:00
.arcconfig Update Phabricator server. 2014-04-07 04:52:24 +00:00
.clang-format Remove redundant "Standard: Cpp11" tag. The LLVM style has used the 2014-07-04 12:08:03 +00:00
.gitignore Update .gitignore to ignore hidden MacOSX Finder droppings 2014-07-16 21:01:17 +00:00
CMakeLists.txt Inline a trivial CMakeLists.txt. 2016-03-03 01:56:23 +00:00
CODE_OWNERS.TXT Add initial CODE_OWNERS.TXT file 2015-07-25 00:44:37 +00:00
LICENSE.TXT Update copyright year to 2015. 2015-03-12 20:14:35 +00:00
README.md
…

README.md

LLVM Linker (lld)

This directory and its subdirectories contain source code for the LLVM Linker, a modular cross platform linker which is built as part of the LLVM compiler infrastructure project.

lld is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt.