MIPS ABI turns using of GOT and dynamic relocations inside out. While
regular ABI uses dynamic relocations to fill up GOT entries MIPS ABI
requires dynamic linker to fills up GOT entries using specially sorted
dynamic symbol table. This affects even dynamic relocations against
symbols which do not require GOT entries creation explicitly, i.e. do
not have any GOT-relocations. So if a preemptible symbol has a dynamic
relocation we anyway have to create a GOT entry for it.
If a non-preemptible symbol has a dynamic relocation against it, dynamic
linker takes it st_value, adds offset and writes down result of the
dynamic relocation. In case of preemptible symbol dynamic linker
performs symbol resolution, writes the symbol value to the GOT entry and
reads the GOT entry when it needs to perform a dynamic relocation.
Differential Revision: http://reviews.llvm.org/D18948
llvm-svn: 266921
Originally, linker scripts were basically an alternative way to specify
options to the command line options. But as we add more features to hanlde
symbols and sections, many member functions needed to be templated.
Now most the members are templated. It is probably time to template the
entire class.
Previously, LinkerScript is an executor of the linker script as well as
a storage of linker script configurations. This is not suitable to template
the class because when we are reading linker script files, we don't know
the ELF type yet, so we can't instantiate ELF-templated classes.
In this patch, I defined a new class, ScriptConfiguration, to store
linker script configurations. ScriptParser writes parse results to it,
and LinkerScript uses them.
Differential Revision: http://reviews.llvm.org/D19302
llvm-svn: 266908
It is now redundant. Writer.cpp can reason that 2 dynamic relocations
are needed: one to find the final got entry address and one to fill the
got entry.
llvm-svn: 266876
This requires adding a few more expression types, but is already a small
simplification. Having Writer.cpp know the exact expression will also
allow further simplifications.
llvm-svn: 266604
* Do script driven layout only if SECTIONS section exist.
Initial commit message:
[ELF] - Implemented basic location counter support.
This patch implements location counter support.
It also separates assign addresses for sections to assignAddressesScript() if it scipt exists.
Main testcase is test/ELF/linkerscript-locationcounter.s, It contains some work with location counter. It is basic now.
Implemented location counter assignment and '+' operations.
Patch by myself with LOTS of comments and design suggestions from Rui Ueyama.
Differential revision: http://reviews.llvm.org/D18499
llvm-svn: 266526
This patch implements location counter support.
It also separates assign addresses for sections to assignAddressesScript() if it scipt exists.
Main testcase is test/ELF/linkerscript-locationcounter.s, It contains some work with location counter. It is basic now.
Implemented location counter assignment and '+' operations.
Patch by myself with LOTS of comments and design suggestions from Rui Ueyama.
Differential revision: http://reviews.llvm.org/D18499
llvm-svn: 266457
The _gp_disp symbol designates offset between start of function and 'gp'
pointer into GOT. The following code is a typical MIPS function preamble
used to setup $gp register:
lui $gp, %hi(_gp_disp)
addi $gp, $gp, %lo(_gp_disp)
To calculate R_MIPS_HI16 / R_MIPS_LO16 relocations results we use
the following formulas:
%hi(_gp - P + A)
%lo(_gp - P + A + 4),
where _gp is a value of _gp symbol, A is addend, and P current address.
The R_MIPS_LO16 relocation references _gp_disp symbol is always the second
instruction. That is why we need four byte adjustments. The patch assigns
R_PC type for R_MIPS_LO16 relocation and adjusts its addend by 4. That fix
R_MIPS_LO16 calculation.
For details see p. 4-19 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
Differential Revision: http://reviews.llvm.org/D19115
llvm-svn: 266368
We never need to iterate over the K,V pairs, so we can avoid copying the
key as MapVector does.
This is a small speedup on most benchmarks.
llvm-svn: 266364
That was removed in r266304, but leads to warnings by Clang.
Thanks to Rafael Espíndola for pointing on that.
Though I think change was legal from point of C++.
llvm-svn: 266306
They are unnecessary, as the dynamic loader can apply the original relocations
directly. This was also resulting in the creation of copy relocations in PIEs.
Differential Revision: http://reviews.llvm.org/D19089
llvm-svn: 266273
This simplifies the code by allowing us to remove the visibility argument
to functions that create synthetic symbols.
The only functional change is that the visibility of the MIPS "_gp" symbol
is now hidden. Because this symbol is defined in every executable or DSO, it
would be difficult to observe a visibility change here.
Differential Revision: http://reviews.llvm.org/D19033
llvm-svn: 266208
We need to ensure that the address of an undefined weak symbol evaluates to
zero. We were getting this right for non-PIC executables (where the symbol
can be evaluated directly) and for DSOs (where we emit a symbolic relocation
for these symbols, as they are preemptible). But we weren't getting it right
for PIEs. Probably the simplest way to ensure that these symbols evaluate
to zero is by not creating a relocation in .got for them.
Differential Revision: http://reviews.llvm.org/D19044
llvm-svn: 266161
With this patch we use the first scan over the relocations to remember
the information we found about them: will them be relaxed, will a plt be
used, etc.
With that the actual relocation application becomes much simpler. That
is particularly true for the interfaces in Target.h.
This unfortunately means that we now do two passes over relocations for
non SHF_ALLOC sections. I think this can be solved by factoring out the
code that scans a single relocation. It can then be used both as a scan
that record info and for a dedicated direct relocation of non SHF_ALLOC
sections.
I also think it is possible to reduce the number of enum values by
representing a target with just an OutputSection and an offset (which
can be from the start or end).
This should unblock adding features like relocation optimizations.
llvm-svn: 266158
The _gp* family of symbols is defined as an offset in .got, and it is
not at all clear what should happen when .got is not defined.
This will allow some simplifications on how these symbols are handled.
llvm-svn: 266063
It is possible that the same symbol referenced by two kinds of
relocations at the same time. The first type requires say GOT entry
creation, the second type requires dynamic copy relocation. For MIPS
targets they might be R_MIPS_GOT16 and R_MIPS_HI16 relocations. For X86
target they might be R_386_GOT32 and R_386_32 respectively.
Now LLD never creates GOT entry for a symbol if this symbol already has
related copy relocation. This patch solves this problem.
Differential Revision: http://reviews.llvm.org/D18862
llvm-svn: 265910
Now MustBeInDynSym is only true if the symbol really must be in the
dynamic symbol table.
IsUsedInRegularObj is only true if the symbol is used in a .o or -u. Not
a .so or a .bc.
A benefit is that this is now done almost entirilly during symbol
resolution. The only exception is copy relocations because of aliases.
This includes a small fix in that protected symbols in .so don't force
executable symbols to be exported.
This also opens the way for implementing internalize for -shared.
llvm-svn: 265826
Previously, we supported only one hash function, FNV-1, so
BuildIdSection directly handled hash computation. In this patch,
I made BuildIdSection an abstract class and defined two subclasses,
BuildIdFnv1 and BuildIdMd5.
llvm-svn: 265737
This requires knowing input section offsets in output sections before
scanRelocs. This is generally a good thing and should allow further
simplifications in the creation of dynamic relocations.
llvm-svn: 265673
We have to differentiate undefined symbols from bitcode and undefined
symbols from other sources.
Undefined symbols from bitcode should not inhibit the symbol being
internalized. Undefined symbols from other sources should.
llvm-svn: 265536
ELF and program header are not part of OutputSections list anymore.
That helps to avoid having and working with functions like dummySectionsNum().
Still keeping them as sections helps to simplify the code.
Differential revision: http://reviews.llvm.org/D18743
llvm-svn: 265522
Where Clang's AArch64 backend seems to differ from the X86 backend is
that it tends to use the GOT more aggressively.
After getting CloudABI PIEs working on x86-64, I noticed that accessing
global variables would still crash on aarch64. Tracing it down, it turns
out that the GOT was filled with entries assuming the base address was
zero.
It turns out that we skip generating relocations for GOT entries in case
the relocation pointing towards the GOT is relative. Whether the thing
pointing to the GOT is absolute or relative shouldn't make any
difference; the GOT entry itself should contain the absolute address,
thus needs a relocation regardless.
Approved by: rafael
Differential Revision: http://reviews.llvm.org/D18739
llvm-svn: 265453
For each copy relocation that we create, look through the DSO's symbol table
for aliases and create a dynamic symbol for each one. This causes the copy
relocation to correctly interpose any aliases.
Copy relocations are relatively uncommon (on my machine, 56% of binaries in
/usr/bin have no copy relocations probably due to being PIEs, 97% of them
have <10, and the binary with the largest number of them has 97) so it's
probably fine to do this in a relatively inefficient way.
Differential Revision: http://reviews.llvm.org/D18731
llvm-svn: 265354
Our symbol representation was redundant, and some times would get out of
sync. It had an Elf_Sym, but some fields were copied to SymbolBody.
Different parts of the code were checking the bits in SymbolBody and
others were checking Elf_Sym.
There are two general approaches to fix this:
* Copy the required information and don't store and Elf_Sym.
* Don't copy the information and always use the Elf_Smy.
The second way sounds tempting, but has a big problem: we would have to
template SymbolBody. I started doing it, but it requires templeting
*everything* and creates a bit chicken and egg problem at the driver
where we have to find ELFT before we can create an ArchiveFile for
example.
As much as possible I compared the test differences with what gold and
bfd produce to make sure they are still valid. In most cases we are just
adding hidden visibility to a local symbol, which is harmless.
In most tests this is a small speedup. The only slowdown was scylla
(1.006X). The largest speedup was clang with no --build-id, -O3 or
--gc-sections (i.e.: focus on the relocations): 1.019X.
llvm-svn: 265293
Extracts code for initializing dummies sections
to avoid possible duplication in following patches.
Differential review: http://reviews.llvm.org/D18691
llvm-svn: 265159
Some functions in Writer reports error using HasError, and some reports
their return values. This patch makes them to consistently use HasError.
llvm-svn: 265156
fixAbsoluteSymbols fixes linker-created symbol addresses. Since we don't
create such symbols for relocatable output, we don't need to call this
function.
llvm-svn: 265154
assignAddressesRelocatable function did not set addresses to sections
despite its name. What it actually did is to set file offsets to sections.
assignAddresses function assigned addresses and file offsets to sections.
So there was a confusion what they were doing, and they had duplicate code.
This patch separates file offset assignments from address assignments.
A new function, assignFileOffsets assign file offsets. assignAddresses
do not care about file offsets anymore.
llvm-svn: 265151
The extra fix is to note that it still requires copy relocations.
Original message:
Change how we handle R_MIPS_LO16.
Mips aligns PT_LOAD to 16 bits (0x10000). That means that the lower 16
bits are always the same, so we can, effectively, say that the
relocation is relative.
P.S.: Suggestions for a better name for the predicate are welcome :-)
llvm-svn: 265150
That is consistent with other symbols: _edata, _etext
and can help to avoid duplicate code.
Differential revision: http://reviews.llvm.org/D18655
llvm-svn: 265129
Some targets might require creation of thunks. For example, MIPS targets
require stubs to call PIC code from non-PIC one. The patch implements
infrastructure for thunk code creation and provides support for MIPS
LA25 stubs. Any MIPS PIC code function is invoked with its address
in register $t9. So if we have a branch instruction from non-PIC code
to the PIC one we cannot make the jump directly and need to create a small
stub to save the target function address.
See page 3-38 ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
- In relocation scanning phase we ask target about thunk creation necessity
by calling `TagetInfo::needsThunk` method. The `InputSection` class
maintains list of Symbols requires thunk creation.
- Reassigning offsets performed for each input sections after relocation
scanning complete because position of each section might change due
thunk creation.
- The patch introduces new dedicated value for DefinedSynthetic symbols
DefinedSynthetic::SectionEnd. Synthetic symbol with that value always
points to the end of the corresponding output section. That allows to
escape updating synthetic symbols if output sections sizes changes after
relocation scanning due thunk creation.
- In the `InputSection::writeTo` method we write thunks after corresponding
input section. Each thunk is written by calling `TargetInfo::writeThunk` method.
- The patch supports the only type of thunk code for each target. For now,
it is enough.
Differential Revision: http://reviews.llvm.org/D17934
llvm-svn: 265059
If we make R_MIPS_LO16 a relative relocation, linker:
- never creates R_MIPS_COPY relocation for it
- attempts to create R_MIPS_REL32 dynamic relocation if R_MIPS_LO16's
target is a preemptible symbol
Differential Revision: http://reviews.llvm.org/D18607
llvm-svn: 264956
gold and bfd do not include the undefined locals in symtab.
We have no reasons to support that either.
That fixes PR27016
Differential revision: http://reviews.llvm.org/D18554
llvm-svn: 264843
Mips aligns PT_LOAD to 16 bits (0x10000). That means that the lower 16
bits are always the same, so we can, effectively, say that the
relocation is relative.
llvm-svn: 264761
When a tls access is optimized, a group of relocations is converted at a
time.
We were already skipping relocations that were optimized out in
relocate, but not in scanRelocs.
This is a small optimization. I got here while working on a patch that
will always keep scanRelocs and relocate in sync.
llvm-svn: 264048
Now local symbols have SymbolBody so we can handle all kind of symbols
in the GotSection::addEntry method. The patch moves the code from
addMipsLocalEntry to addEntry. NFC.
Differential Revision: http://reviews.llvm.org/D18302
llvm-svn: 264032
-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
We want to make SymbolBody the central place to query symbol information.
This patch also renames canBePreempted to isPreemptible because I feel that
the latter is slightly better (the former is three words and the latter
is two words.)
llvm-svn: 263386
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
At least Linux has the kernel configuration to include the first page
of the executable into core files. We want build ID section to be
included in core files to identify them.
Here is the link to the description about the kernel configuration.
097f70b3c4/fs/Kconfig.binfmt (L46)
llvm-svn: 263351
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
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
We can argue about a maximum alignment of a group of symbols,
but for each symbol, there is only one alignment.
So it is a bit weird that each symbol has a "maximum alignment".
llvm-svn: 263151
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
It was a badly specified hack for when a tls relocation should be
propagated to the dynamic relocation table.
This replaces it with a not as bad hack of saying that a local dynamic
tls relocation is never preempted.
I will try to remove even that second hack in the next patch.
llvm-svn: 262955
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
Get rid of few accessors in that class, and replace
them with direct fields access.
Differential revision: http://reviews.llvm.org/D17879
llvm-svn: 262796
Patch changes all relocations types to be uint32_t and also
fixes some dependent inconsistency in callers code.
Differential revision: http://reviews.llvm.org/D17882
llvm-svn: 262793
The rules for when we can relax tls relocations are target independent.
The only things that are target dependent are the relocation values.
llvm-svn: 262748
SymbolBody constructor and friends take isFunc and isTLS boolean arguments.
ELF symbols have already a type so than be easily passed as argument.
If we want to support another type, this scheme is not good enough, that is,
the current code logic would require passing another `bool isObject` around.
Up to two argument, this stretching exercise was a little bit goofy but
still acceptable, but with more types to support, is just too much, IMHO.
Change the code so that the type is passed instead.
Differential Revision: http://reviews.llvm.org/D17871
llvm-svn: 262684
When generating relocatable output SHT_NOBITS sections
were still occupy the file space.
Differential revision: http://reviews.llvm.org/D17857
llvm-svn: 262650
There was a known limitation for -r option:
relocations against local symbols were not supported.
For example rel[a].eh_frame sections contained relocations against sections
and that was not supported for -r before. Patch fixes that.
Differential review: http://reviews.llvm.org/D17813
llvm-svn: 262590
As was suggested in mails, this patch implements edata/etext
symbols in a more direct way.
It iterates through PT_LOADs.
Result seems to be the same and equal to gold output.
Differential revision: http://reviews.llvm.org/D17755
llvm-svn: 262369
__start_/__end_ <section-name> symbols and other specials like:
preinit_array_start/end
init_array_start/end
fini_array_start/end
should not be created by linker when creating relocatable files.
Differential revision: http://reviews.llvm.org/D17774
llvm-svn: 262366
Regarding the comment, it is out of context because it describes
what it does not do there. It got too long because it was originally
two different comments that were simply merged together.
The semantics is described in fixAbsoluteSymbols, so we don't need it.
llvm-svn: 262031
https://docs.oracle.com/cd/E53394_01/html/E54766/u-etext-3c.html
It is said that:
_etext - The address of _etext is the first
location after the last read-only loadable segment.
_edata - The address of _edata is the first
location after the last read-write loadable segment.
_end - If the address of _edata is greater than the address
of _etext, the address of _end is same as the address of _edata.
In real life _end and _edata has different values for that case.
Both gold/bfd set _edata to the end of the last non SHT_NOBITS section.
This patch do the same for consistency.
It should fix the https://llvm.org/bugs/show_bug.cgi?id=26729.
Differential revision: http://reviews.llvm.org/D17601
llvm-svn: 262019
For shared libraries we allow any weak undefined symbol to eventually be
resolved, even if we never see a definition in another .so. This matches
the behavior when handling other undefined symbols in a shared library.
For executables, we require seeing a definition in a .so or resolve it
to zero. This is also similar to how non weak symbols are handled.
llvm-svn: 262017
Rafael Espindola