Export definitions in a module definition file is as follows:
exportedname[=internalname] [@ordinal [NONAME]] [PRIVATE] [DATA]
Previously we did not support =internalname, so users couldn't export
symbols from a DLL with a different name.
llvm-svn: 207827
In general the linker scripts's GROUP command works like a pair
of command line options --start-group/--end-group. But there is
a difference in the files look up algorithm.
The --start-group/--end-group commands use a trivial approach:
a) If the path has '-l' prefix, add 'lib' prefix and '.a'/'.so'
suffix and search the path through library search directories.
b) Otherwise, use the path 'as-is'.
The GROUP command implements more compicated approach:
a) If the path has '-l' prefix, add 'lib' prefix and '.a'/'.so'
suffix and search the path through library search directories.
b) If the path does not have '-l' prefix, and sysroot is configured,
and the path starts with the / character, and the script being
processed is located inside the sysroot, search the path under
the sysroot. Otherwise, try to open the path in the current
directory. If it is not found, search through library search
directories.
https://www.sourceware.org/binutils/docs-2.24/ld/File-Commands.html
The patch reviewed by Shankar Easwaran, Rui Ueyama.
llvm-svn: 207769
When creating a .lib file, we should strip the leading underscore,
but should not strip stdcall atsign suffix. Otherwise produced .lib
files cannot be linked.
llvm-svn: 207729
Previously the input file for the lib.exe command would be removed
as soon as the command exits, so we couldn't write a test to check
the file contents are correct.
This patch adds /lldmoduledeffile: option to retain a copy of the
temporary file at the given file path, so that you can see the file
if you want.
llvm-svn: 207727
Linker should create _imp_ symbols for local use only when such
symbols cannot be resolved in any other way. If it overrides real
imported symbols, such symbols remain virtually unresolved without
error, causing odd issues. I observed that a program linked with
LLD entered an infinite loop before reaching main() because of
this issue.
This patch moves the virtual file creating _imp_ symbols to the
very end of the input file list. Previously, the file is at the end
of the library file group. Linker might revisit the group many times,
so it was not really at the end of the input file list.
llvm-svn: 207605
1. Re-implement PLT entries and dynamic relocations emitting to keep PLT
and relocations table in a consistent state.
2. Initialize st_value and st_other fields for dynamic symbols table
entry if this entry corresponds to an external function which address is
taken in a non-PIC executable. In that case the st_value field holds an
address of the function's PLT entry. Also set STO_MIPS_PLT bit in the
st_other field.
llvm-svn: 207494
Implicit symbol for local use implemented in r207141 was not fully
compatible with MSVC link.exe. In r207141, I implemented the feature
in such way that implicit symbols are defined only when they are
exported with /EXPORT option.
After that I found that implicit symbols are defined not only for
dllexported symbols but for all defined symbols. Actually _imp_
implicit symbols have no relationship with the dllexport feature. You
could add _imp_ to any symbol to get a pointer to the symbol, whether
the symbol is dllexported or not. It looks pretty weird to me but
that's what we want if link.exe behaves that way.
Here is a bit about the implementation: Creating all implicit symbols
beforehand is going to be a huge waste of resource. This feature is
rarely used, and MSVC link.exe even prints out a warning message when
it finds this feature is being used. So we create implicit symbols
on demand. There is an archive file that creates implicit symbols when
they are needed.
llvm-svn: 207476
This patch is to fix a compatibility issue with MSVC link.exe as to
use of dllexported symbols inside DLL.
A DLL exports two symbols for a function. One is non-decorated one,
and the other is with __imp_ prefix. The former is a function that
you can directly call, and the latter is a pointer to the function.
These dllexported symbols are created by linker for programs that
link against the DLL. So, I naturally believed that __imp_ symbols
become available when you once create a DLL and link against it, but
they don't exist until then. And that's not true.
MSVC link.exe is smart enough to allow users to use __imp_ symbols
locally. That is, if a symbol is specified with /export option, it
implicitly creates a new symbol with __imp_ prefix as a pointer to
the exported symbol. This feature allows the following program to
be linked and run, although _imp__hello is not defined in this code.
#include <stdio.h>
__declspec(dllexport)
void hello(void) { printf("Hello\n"); }
extern void (*_imp__hello)(void);
int main() {
_imp__hello();
return 0;
}
MSVC link.exe prints out the following warning when linking it.
LNK4217: locally defined symbol _hello imported in function _main
Using __imp_ symbols locally is I think not a good coding style. One
should just take an address using "&" operator rather than appending
__imp_ prefix. However, there are programs in the wild that depends
on this link.exe's behavior, so we need this feature.
llvm-svn: 207141
Not all symbols are decorated with an underscore in x86. You can
write undecorated symbols in assembly, for example. Thus this
assertion is too strong.
llvm-svn: 207125
We don't use sections with IMAGE_SYM_DEBUG attribute so we basically
want to the symbols for them when reading symbol table. When we skip
them, we need to skip auxiliary symbols too. Otherwise weird error
would happen because aux symbols would be interpreted as regular ones.
llvm-svn: 206931
definition below all of the header #include lines, LLD edition.
IF you want to know more details about this, you can see the recent
commits to Debug.h in LLVM. This is just the LLD segment of a cleanup
I'm doing globally for this macro.
llvm-svn: 206851
Currently LLD supports --defsym only in the form of
--defsym=<symbol>=<integer>, where the integer is interpreted as the
absolute address of the symbol. This patch extends it to allow other
symbol name to be given as an RHS value. If a RHS value is a symbol
name, the LHS symbol will be defined as an alias for the RHS symbol.
Internally, a LHS symbol is represented as a zero-size defined atom
who has an LayoutAfter reference to an undefined atom, whose name is
the RHS value. Everything else is already implemented -- Resolver
will resolve the undefined symbol, and the layout pass will layout
the two atoms at the same location. Looks like it's working fine.
Note that GNU LD supports --defsym=<symbol>=<symbol>+<addend>. That
feature is out of scope of this patch.
Differential Revision: http://reviews.llvm.org/D3332
llvm-svn: 206417
a couple of new virtual functions.
Follow-up to the rL203408. Two virtual functions `createRelocationReference()`
responsible for creation of `ELFReference` have been replaced by a couple of
new virtual functions `createRelocationReferences()` (plural). Each former
function creates a //single// ELFReference for a specified `Elf_Rela`
or `Elf_Rel` relocation records. The new functions responsible for creation
of //all// relocation references for provided symbol.
For all targets except MIPS there are no functional changes.
MIPS ABI has a notion of //paired// relocations. An effective addend of such
relocations are calculated using addends of both pair's members.
Each `R_MIPS_HI16` and `R_MIPS_GOT16` (for local symbols) relocations must have
an associated `R_MIPS_LO16` entry immediately following it in the list
of relocations. Immediately does not mean "next record" in relocations section
but "next record referenced the same symbol". Moreover a single `R_MIPS_LO16`
relocation can be paired with multiple preceding `R_MIPS_HI16/R_MIPS_GOT16`
relocations.
The paired relocation can have offsets belong to the different symbols.
That is why we need to have access to list of all relocations during
construction of `ELFReference` for MIPS target.
The patch reviewed by Shankar Easwaran.
llvm-svn: 206102
Seems getSomething() is more common naming scheme than just a noun
to get something, so renaming these members.
Differential Revision: http://llvm-reviews.chandlerc.com/D3285
llvm-svn: 205589
"x.empty()" is more idiomatic than "x.size() == 0". This patch is to
add such method and use it in LLD.
Differential Revision: http://llvm-reviews.chandlerc.com/D3279
llvm-svn: 205558
.gnu.linkonce sections are similar to section groups.
They were supported before section groups existed and provided a way
to resolve COMDAT sections using a different design.
There are few implementations that use .gnu.linkonce sections
to store simple floating point constants which doesnot require complex section
group support but need a way to store only one copy of the floating point
constant in a binary.
.gnu.linkonce based symbol resolution achieves that.
Review : http://llvm-reviews.chandlerc.com/D3242
llvm-svn: 205280
This reverts commit 5d5ca72a7876c3dd3dd1db83dc6a0d74be9e2cd1.
Discuss on a better design to raise error when there is a similar group with Gnu
linkonce sections and COMDAT sections.
llvm-svn: 205224
.gnu.linkonce sections are similar to section groups. They were supported before
section groups existed and provided a way to resolve COMDAT sections using a
different design. There are few implementations that use .gnu.linkonce sections
to store simple floating point constants which doesnot require complex section
group support but need a way to store only one copy of the floating point
constant. .gnu.linkonce based symbol resolution achieves that.
llvm-svn: 205163
This patch is to support --defsym option for ELF file format/GNU-compatible
driver. Currently it takes a symbol name followed by '=' and a number. If such
option is given, the driver sets up an absolute symbol with the specified
address. You can specify multiple --defsym options to define multiple symbols.
GNU LD's --defsym provides many more features. For example, it allows users to
specify another symbol name instead of a number to define a symbol alias, or it
even allows a symbol plus an offset (e.g. --defsym=foo+3) to define symbol-
relative alias. This patch does not support that, but will be supported in
subsequent patches.
Differential Revision: http://llvm-reviews.chandlerc.com/D3208
llvm-svn: 205029
These classes are declared in a .cpp file but not used in the same compliation
unit. They seems to have been copy-and-pasted from ELFReader.h.
llvm-svn: 204988
of GOT.
* Read addend for R_MIPS_GOT16 relocation.
* Put only high 16 bits of symbol + addend into GOT entries for
locally visible symbols.
llvm-svn: 204247
COMDAT_SELECT_LARGEST is a COMDAT type that make linker to choose the largest
definition from among all of the definition of a symbol. If the size is the
same, the choice is arbitrary.
Differential Revision: http://llvm-reviews.chandlerc.com/D3011
llvm-svn: 204172
The COFF spec says that the SectionNumber field in the symbol table is 16 bit
signed type, but MSVC treats the field as if it is unsigned.
llvm-svn: 203901
This results in some simplifications to the code where an OwningPtr had to
be used with the previous api and then ownership moved to a unique_ptr for
the rest of lld.
llvm-svn: 203809
An object whose machine type header value is unknown looks a bit odd but
is valid. If an object contains only machine-type-independent data, you
can leave the type field unspecified. Some files in oldname.lib are such
object files.
llvm-svn: 203752
Summary:
COMDAT_SELECT_SAME_SIZE is a COMDAT type that I presume exist only in COFF.
The semantics of the type is that linker should merge such COMDAT sections if
their sizes are the same. Otherwise it's an error.
Reviewers: Bigcheese, shankarke, kledzik
CC: llvm-commits
Differential Revision: http://llvm-reviews.chandlerc.com/D2996
llvm-svn: 203308
Just like x86 exception handler table, the table for x64 needs to be sorted
so that runtime can binary search on it. Unlike x86, the table entry for x64
has multiple fields, and they need to be sorted according to its BeginAddress
field. This patch also fixes a bug in relocations.
llvm-svn: 202874
It looks like the contents of the table need to be sorted according to its
value, so that the runtime can find the entry by binary search. I'm not 100%
sure if we really have to do that, but at least I can say it's safe to do
because the contents of .sxdata is just a list of exception handlers' RVAs.
llvm-svn: 202550
If all input files are compatible with Structured Exception Handling, linker
is supposed to create an exectuable with a table for SEH handlers. The table
consists of exception handlers entry point addresses.
The basic idea of SEH in x86 Microsoft ABI is to list all valid entry points
of exception handlers in an read-only memory, so that an attacker cannot
override the addresses in it. In x86 ABI, data for exception handling is mostly
on stack, so it's volnerable to stack overflow attack. In order to protect
against it, Windows runtime uses the table to check a return address, to
ensure that the address is really an valid entry point for an exception handler.
Compiler emits a list of exception handler functions to .sxdata section. It
also emits a marker symbol "@feat.00" to indicate that the object is compatible
with SEH. SEH is a relatively new feature for COFF, and mixing SEH-compatible
and SEH-incompatible objects will result in an invalid executable, so is the
marker.
If all input files are compatible with SEH, LLD emits a SEH table. SEH table
needs to be pointed by Load Configuration strucutre, so when emitting a SEH
table LLD emits it too. The address of a Load Configuration will be stored to
the file header.
llvm-svn: 202248
target_link_libraries(INTERFACE) doesn't bring inter-target dependencies in add_library,
although final targets have dependencies to whole dependent libraries.
It makes most libraries can be built in parallel.
target_link_libraries(PRIVATE) is used to shaared library.
Each dependent library is linked to the target.so, and its user will not see its grandchildren.
For example,
- libclang.so has sufficient libclang*.a(s).
- c-index-test requires just only libclang.so.
FIXME: lld is tweaked minimally. Adding INTERFACE in each library would be better thing.
llvm-svn: 202241
This restores the debug output to how it was before r197727 broke it. This
went undetected because the corresponding test was never run due to broken
feature detection.
llvm-svn: 202079
The sections .rela/.rel.(*) have a alignment of 2 in the final image created by
the linker. This needs to be properly set to the right alignment depending on
the architecture(32/64bits).
llvm-svn: 201740
Rui Ueyama