IFUNC is a GNU extension to the ELF standard that allows a function to
have multiple implementations. A resolver function has to be called at
load time to choose the right one to use. The PLT will contain the entry
to the resolved function, so branching and more indirect jumps can be
avoided at run-time.
This mechanism is usually used when a routine can be made faster using
CPU features that are available in only some models, and a fallback
implementation has to exist for others.
We will use this feature to have two separate memset implementations for
CPUs with and without ERMS (Enhanced REP MOVSB/STOSB) support.
Avoid promotion of static strings to AK::String, instead use
AK::StringView and operator ""sv, to force string view's instead
which avoids allocation of String. This code path isn't hot enough
that it makes a huge difference, but every bit counts.
We had two functions for doing mostly the same thing. Combine both
of them into String::find() and use that everywhere.
Also add some tests to cover basic behavior.
The expression address - candidate.address can yield a value that
cannot safely be converted to an i32 which would result in
binary_search failing to find some symbols.
By constraining two implementations, the compiler will select the best
fitting one. All this will require is duplicating the implementation and
simplifying for the `void` case.
This constraining also informs both the caller and compiler by passing
the callback parameter types as part of the constraint
(e.g.: `IterationFunction<int>`).
Some `for_each` functions in LibELF only take functions which return
`void`. This is a minimal correctness check, as it removes one way for a
function to incompletely do something.
There seems to be a possible idiom where inside a lambda, a `return;` is
the same as `continue;` in a for-loop.
For whatever reason, symbolication was doing an O(n) walk of all the
symbols, despite having sorted them beforehand.
Changing this to a binary_search() makes symbolication noticeably
faster and improves Profiler startup time.
We were using ELF::Image::section(0) to indicate the "undefined"
section, when what we really wanted was just Optional<Section>.
So let's use Optional instead. :^)
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
The name-to-section lookup table was only used in a handful of places,
and none of them were calling it nearly enough to justify building
a cache for it in the first place. So let's get rid of it and reduce
startup time by a little bit. :^)
Section names are referred to by offset and length. We do not check
(and probably should not check) whether these names overlap in any way.
This opened the door to many sections (in this example: about 2700)
forcing ELF::Image::m_sections to contain endless copies of the same
huge string (in this case: 882K).
Fix this by loading only the first PAGE_SIZE bytes of each name.
Since section names are only relevant for relocations and debug
information and most section names are hard-coded (and far below 4096
bytes) anyway, this should be no restriction at all for 'normal'
executables.
Found by OSS-Fuzz:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=29187
