Support MASM's REPEAT, FOR, FORC, and WHILE macro-like directives.
Also adds support for macro argument substitution inside quoted strings, and additional testing for macro directives.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D89732
MASM interprets strings in expression contexts as integers expressed in big-endian base-256, treating each character as its ASCII representation.
This completely eliminates the need to special-case single-character strings.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D90788
Allow single-quoted strings and double-quoted character values, as well as doubled-quote escaping.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D89731
Allows the MACRO directive to define macro procedures with parameters and macro-local symbols.
Supports required and optional parameters (including default values), and matches ml64.exe for its macro-local symbol handling (up to 65536 macro-local symbols in any translation unit).
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D89729
A SMLoc allows MCStreamer to report location-aware diagnostics, which
were previously done by adding SMLoc to various methods (e.g. emit*) in an ad-hoc way.
Since the file:line is most important, the column is less important and
the start token location suffices in many cases, this patch reverts
b7e7131af2
```
// old
symbol-binding-changed.s:6:8: error: local changed binding to STB_GLOBAL
.globl local
^
// new
symbol-binding-changed.s:6:1: error: local changed binding to STB_GLOBAL
.globl local
^
```
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D90511
This patch lets the bb_addr_map (renamed to __llvm_bb_addr_map) section use a special section type (SHT_LLVM_BB_ADDR_MAP) instead of SHT_PROGBITS. This would help parsers, dumpers and other tools to use the sh_type ELF field to identify this section rather than relying on string comparison on the section name.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D88199
MASM allows arbitrary whitespace around the Intel dot operator, especially when used for struct field lookup
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D88450
Support the "alias" directive.
Required support for emitWeakReference in MCWinCOFFStreamer.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D87403
Add support for .radix directive, and radix specifiers [yY] (binary), [oOqQ] (octal), and [tT] (decimal).
Also, when lexing MASM integers, require radix specifier; MASM requires that all literals without a radix specifier be treated as in the default radix. (e.g., 0100 = 100)
Relanding D87400, now with fewer ms-inline-asm tests broken!
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D88337
Add support for .radix directive, and radix specifiers [yY] (binary), [oOqQ] (octal), and [tT] (decimal).
Also, when lexing MASM integers, require radix specifier; MASM requires that all literals without a radix specifier be treated as in the default radix. (e.g., 0100 = 100)
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D87400
MASM structs are end-padded to have size a multiple of the smaller of the requested alignment and the size of their largest field (taken recursively, if they have a field of STRUCT type).
This matches the behavior of ml.exe and ml64.exe. Our original implementation followed the MASM 6.0 documentation, which instead specified that MASM structs were padded to a multiple of their requested alignment.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D87248
Add signed aliases for integral types, as well as the "DF" abbreviation for the FWORD type.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D87246
MASM allows variables defined by equate statements to be used in expressions.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D86946
MASM aligns fields to the _minimum_ of the STRUCT alignment value and the size of the next field.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D86945
Add support for line continuations (the "backslash operator") in MASM by modifying the Parser's Lex method.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D83347
This ensures that you get the same output regardless if generating
code directly to an object file or if generating assembly and
assembling that.
Add implementations of the EmitARM64WinCFI*() methods in
AArch64TargetAsmStreamer, and fill in one blank in MCAsmStreamer.
Add corresponding directive handlers in AArch64AsmParser and
COFFAsmParser.
Some SEH directive names have been picked to match the prior art
for SEH assembly directives for x86_64, e.g. the spelling of
".seh_startepilogue" matching the preexisting ".seh_endprologue".
For the directives for saving registers, the exact spelling
from the arm64 documentation is picked, e.g. ".seh_save_reg" (to follow
that naming for all the other ones, e.g. ".seh_save_fregp_x"), while
the corresponding one for x86_64 is plain ".seh_savereg" without the
second underscore.
Directives in the epilogues have the same names as in prologues,
e.g. .seh_savereg, even though the registers are restored, not
saved, at that point.
Differential Revision: https://reviews.llvm.org/D86529
Define the platform ID = 10, and simple mappings between platform ID & name.
Reviewed By: MaskRay, cishida
Differential Revision: https://reviews.llvm.org/D85594
Part of https://bugs.llvm.org/show_bug.cgi?id=41734
LTO can drop externally available definitions. Such AssociatedSymbol is
not associated with a symbol. ELFWriter::writeSection() will assert.
Allow a SHF_LINK_ORDER section to have sh_link=0.
We need to give sh_link a syntax, a literal zero in the linked-to symbol
position, e.g. `.section name,"ao",@progbits,0`
Reviewed By: pcc
Differential Revision: https://reviews.llvm.org/D72899
For `.reloc offset, *, *`, currently offset can be a constant or symbol.
This patch makes it support any expression which can be folded to sym+constant.
Reviewed By: stefanp
Differential Revision: https://reviews.llvm.org/D83751
Summary:
Add support for user-defined types to MasmParser, including initialization and field access.
Known issues:
- Omitted entry initializers (e.g., <,0>) do not work consistently for nested structs/arrays.
- Size checking/inference for values with known types is not yet implemented.
- Some ml64.exe syntaxes for accessing STRUCT fields are not recognized.
- `[<register>.<struct name>].<field>`
- `[<register>[<struct name>.<field>]]`
- `(<struct name> PTR [<register>]).<field>`
- `[<variable>.<struct name>].<field>`
- `(<struct name> PTR <variable>).<field>`
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D75306
Summary:
When parsing 64-bit MASM, treat memory operands with unspecified base register as RIP-based.
Documented in several places, including https://software.intel.com/en-us/articles/introduction-to-x64-assembly: "Unfortunately, MASM does not allow this form of opcode, but other assemblers like FASM and YASM do. Instead, MASM embeds RIP-relative addressing implicitly."
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D73227
This features matches ELFAsmParser and makes it possible to use `.section ".llvm.call-graph-profile","n"`
Reviewed By: zequanwu
Differential Revision: https://reviews.llvm.org/D82240
Compiling assembly files when newlines are reduced to line markers within a `.macro` context will generate wrong information in `.debug_line` section.
This patch fixes this issue by evaluating line markers within the macro scope but not when they are used and evaluated.
Reviewed By: probinson
Differential Revision: https://reviews.llvm.org/D80381
According to DWARF standard, is_stmt is a global flag; when set or cleared it should affect subsequent .loc directives.
However llvm assembler handled is_stmt differently: it forced all locations to have is_stmt=1 unless is_stmt was specified explicitly as 0.
The fix utilizes current DWARF state flags to compute correct is_stmt values.
See https://bugs.llvm.org/show_bug.cgi?id=45529 for a detailed issue description.
Reviewers: arsenm, probinson, enderby
Differential Revision: https://reviews.llvm.org/D78102
GNU as emits SHT_PROGBITS .eh_frame by default for .cfi_* directives.
We follow x86-64 psABI and use SHT_X86_64_UNWIND for .eh_frame
Don't error for SHT_PROGBITS .eh_frame on x86-64.
This keeps compatibility with `.section .eh_frame,"a",@progbits` in existing assembly files.
See https://groups.google.com/d/msg/x86-64-abi/7sr4E6THl3g/zUU2UPHOAQAJ
for more discussions.
Reviewed By: joerg
Differential Revision: https://reviews.llvm.org/D76151
* Reorganize tests and add coverage
* Improve diagnostic testing
* Make assert() tests more relevant
* Rename tests to macro-* or altmacro-*
This is not NFC because a (previously untested) diagnostic message is changed.
Summary:
Dollar signed prefixed integers were not allowed by the AsmParser to be
used as Identifiers, differing from the GNU assembler behavior.
This patch updates the parsing of Identifiers to consider such cases as
valid, where the identifier string includes the $ prefix itself. As the
Lexer currently splits these occurrences into separate tokens, those
need to be combined by the AsmParser itself.
Reviewers: efriedma, chill
Reviewed By: efriedma
Subscribers: sdardis, hiraditya, jrtc27, atanasyan, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D75111
Summary: ParsingInlineAsm was a misleading name. These values are only set for MS-style inline assembly.
Reviewed By: rnk
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D75198
This reverts commit 9fe769a961, and re-lands commit c2e272f8cf.
Summary: Add support for ?, DUP, and string initializers, as well as MASM syntax for named data locations.
This version avoids the use of a C++17-only feature, if-statements with initializer.
Reviewers: rnk, thakis
Reviewed By: thakis
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73226
Summary: Add support for ?, DUP, and string initializers, as well as MASM syntax for named data locations.
Reviewers: rnk, thakis
Reviewed By: thakis
Subscribers: merge_guards_bot, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73226
Heads-up message: https://lists.llvm.org/pipermail/llvm-dev/2020-February/139390.html
GNU as started to emit warnings for changed sh_type or sh_flags in 2000.
GNU as>=2.35 will emit errors for most sh_type/sh_flags change, and error for entsize change.
Some cases remain warnings for legacy reasons:
.section .init_array,"ax", @progbits
.section .init_array,"ax", @init_array
# And some obscure sh_flags changes (OS/Processor specific flags)
The rationale of a diagnostic (warning or error) is that sh_type,
sh_flags or sh_entsize changes usually indicate user errors. The values
are taken from the first .section directive. Successive directives are ignored.
We just try to be rigid and emit errors for all sh_type/sh_flags/sh_entsize change.
A possible improvement in the future is to reuse
llvm-readobj/ELFDumper.cpp:getSectionTypeString so that we can name the
type in the diagnostics.
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D73999
Summary:
Many directives are unavailable, and support for others may be limited.
This first draft has preliminary support for:
- conditional directives (including errors),
- data allocation (unsigned types up to 8 bytes, and ALIGN),
- equates/variables (numeric and text),
- and procedure directives (without parameters),
as well as COMMENT, ECHO, INCLUDE, INCLUDELIB, PUBLIC, and EXTERN. Text variables (aka text macros) are expanded in-place wherever the identifier occurs.
We deliberately ignore all ml.exe processor directives.
Prominent features not yet supported:
- structs
- macros (both procedures and functions)
- procedures (with specified parameters)
- substitution & expansion operators
Conditional directives are complicated by the fact that "ifdef rax" is a valid way to check if a file is being assembled for a 64-bit x86 processor; we add support for "ifdef <register>" in general, which requires adding a tryParseRegister method to all MCTargetAsmParsers. (Some targets require backtracking in the non-register case.)
Reviewers: rnk, thakis
Reviewed By: thakis
Subscribers: kerbowa, merge_guards_bot, wuzish, arsenm, dschuff, jyknight, dylanmckay, sdardis, nemanjai, jvesely, mgorny, sbc100, jgravelle-google, hiraditya, aheejin, kbarton, fedor.sergeev, asb, rbar, johnrusso, simoncook, sabuasal, niosHD, jrtc27, MaskRay, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, PkmX, jocewei, jsji, Jim, s.egerton, pzheng, sameer.abuasal, apazos, luismarques, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72680
"linked-to section" is used by the ELF spec. By analogy, "linked-to
symbol" is a good name for the signature symbol. The word "linked-to"
implies a directed edge and makes it clear its relation with "sh_link",
while one can argue that "associated" means an undirected edge.
Also, combine tests and add precise SMLoc to improve diagnostics.
Reviewed By: eugenis, grimar, jhenderson
Differential Revision: https://reviews.llvm.org/D74082
This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.
This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.
This doesn't actually modify StringRef yet, I'll do that in a follow-up.
GCC will accept any case for assembler directives.
For example ".abort" and ".ABORT" (even ".aBoRt")
are equivalent.
https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops
"The names are case insensitive for most targets,
and usually written in lower case."
Change llvm-mc to accept any case for generic directives
or aliases of those directives.
This for Bugzilla #39527.
Differential Revision: https://reviews.llvm.org/D72686
Summary:
Extend D71677 to apply to all branch-target operands, rather than special-casing call instructions.
Also add a regression test for llvm.org/PR44272, since this finishes fixing it.
Reviewers: thakis, rnk
Reviewed By: thakis
Subscribers: merge_guards_bot, hiraditya, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D72417
`APFLoat::convertFromString` returns `Expected` result, which must be
"checked" if the LLVM_ENABLE_ABI_BREAKING_CHECKS preprocessor flag is
set.
To mark an `Expected` result as "checked" we must consume the `Error`
within.
In many cases, we are only interested in knowing if an error occured,
without the need to examine the error info. This is achieved, easily,
with the `errorToBool()` API.
Summary:
Amend MS offset operator implementation, to more closely fit with its MS counterpart:
1. InlineAsm: evaluate non-local source entities to their (address) location
2. Provide a mean with which one may acquire the address of an assembly label via MS syntax, rather than yielding a memory reference (i.e. "offset asm_label" and "$asm_label" should be synonymous
3. address PR32530
Based on http://llvm.org/D37461
Fix broken test where the break appears unrelated.
- Set up appropriate memory-input rewrites for variable references.
- Intel-dialect assembly printing now correctly handles addresses by adding "offset".
- Pass offsets as immediate operands (using "r" constraint for offsets of locals).
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D71436
Summary:
This is documented as the appropriate template modifier for call operands.
Fixes PR44272, and adds a regression test.
Also adds support for operand modifiers in Intel-style inline assembly.
Reviewers: rnk
Reviewed By: rnk
Subscribers: merge_guards_bot, hiraditya, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D71677
Summary:
Most libraries are defined in the lib/ directory but there are also a
few libraries defined in tools/ e.g. libLLVM, libLTO. I'm defining
"Component Libraries" as libraries defined in lib/ that may be included in
libLLVM.so. Explicitly marking the libraries in lib/ as component
libraries allows us to remove some fragile checks that attempt to
differentiate between lib/ libraries and tools/ libraires:
1. In tools/llvm-shlib, because
llvm_map_components_to_libnames(LIB_NAMES "all") returned a list of
all libraries defined in the whole project, there was custom code
needed to filter out libraries defined in tools/, none of which should
be included in libLLVM.so. This code assumed that any library
defined as static was from lib/ and everything else should be
excluded.
With this change, llvm_map_components_to_libnames(LIB_NAMES, "all")
only returns libraries that have been added to the LLVM_COMPONENT_LIBS
global cmake property, so this custom filtering logic can be removed.
Doing this also fixes the build with BUILD_SHARED_LIBS=ON
and LLVM_BUILD_LLVM_DYLIB=ON.
2. There was some code in llvm_add_library that assumed that
libraries defined in lib/ would not have LLVM_LINK_COMPONENTS or
ARG_LINK_COMPONENTS set. This is only true because libraries
defined lib lib/ use LLVMBuild.txt and don't set these values.
This code has been fixed now to check if the library has been
explicitly marked as a component library, which should now make it
easier to remove LLVMBuild at some point in the future.
I have tested this patch on Windows, MacOS and Linux with release builds
and the following combinations of CMake options:
- "" (No options)
- -DLLVM_BUILD_LLVM_DYLIB=ON
- -DLLVM_LINK_LLVM_DYLIB=ON
- -DBUILD_SHARED_LIBS=ON
- -DBUILD_SHARED_LIBS=ON -DLLVM_BUILD_LLVM_DYLIB=ON
- -DBUILD_SHARED_LIBS=ON -DLLVM_LINK_LLVM_DYLIB=ON
Reviewers: beanz, smeenai, compnerd, phosek
Reviewed By: beanz
Subscribers: wuzish, jholewinski, arsenm, dschuff, jyknight, dylanmckay, sdardis, nemanjai, jvesely, nhaehnle, mgorny, mehdi_amini, sbc100, jgravelle-google, hiraditya, aheejin, fedor.sergeev, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, MaskRay, zzheng, edward-jones, atanasyan, steven_wu, rogfer01, MartinMosbeck, brucehoult, the_o, dexonsmith, PkmX, jocewei, jsji, dang, Jim, lenary, s.egerton, pzheng, sameer.abuasal, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70179
Summary:
Implement support for hexadecimal escape sequences to match how GNU 'as'
handles them. I.e., read all hexadecimal characters and truncate to the
lower 16 bits.
Reviewers: nickdesaulniers, jcai19
Subscribers: llvm-commits, hiraditya
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68598
llvm-svn: 374018
It broke MC/AsmParser/directive_ascii.s on all bots:
Assertion failed: (Index < Length && "Invalid index!"), function operator[],
file ../../llvm/include/llvm/ADT/StringRef.h, line 243.
llvm-svn: 373898
Summary:
Implement support for hexadecimal escape sequences to match how GNU 'as'
handles them. I.e., read all hexadecimal characters and truncate to the
lower 16 bits.
Reviewers: nickdesaulniers
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68483
llvm-svn: 373888
Also improve assembler parser register validation for .seh_ directives.
This requires moving X86-specific seh directive handling into the x86
backend, which addresses some assembler FIXMEs.
Differential Revision: https://reviews.llvm.org/D66625
llvm-svn: 370533
Debug sections are special in that they can contain relocations against
symbols that are not present in the final output (i.e. not live).
However it is also possible to have R_WASM_TABLE_INDEX relocations
against symbols that don't have a table index assigned (since they are
not address taken by actual code.
Fixes: https://github.com/emscripten-core/emscripten/issues/9023
Differential Revision: https://reviews.llvm.org/D66435
llvm-svn: 369423
Now that we've moved to C++14, we no longer need the llvm::make_unique
implementation from STLExtras.h. This patch is a mechanical replacement
of (hopefully) all the llvm::make_unique instances across the monorepo.
llvm-svn: 369013
Summary:
This patch keeps track of MCSymbols created for blocks that were
referenced in inline asm. It prevents creating a new symbol which
doesn't refer to the block.
Inline asm may have a reference to a label. The asm parser however
doesn't recognize it as a label and tries to create a new symbol. The
result being that instead of the original symbol (e.g. ".Ltmp0") the
parser replaces it in the inline asm with the new one (e.g. ".Ltmp00")
without updating it in the symbol table. So the machine basic block
retains the "old" symbol (".Ltmp0"), but the inline asm uses the new one
(".Ltmp00").
Reviewers: nickdesaulniers, craig.topper
Subscribers: nathanchance, javed.absar, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D65304
llvm-svn: 368477
This patch replaces a TODO comment with a call to `report_fatal_error`.
The path that reaches the added call to `report_fatal_error` manifestly
dereferences a null pointer.
llvm-svn: 368048
assembly command
'macCatalyst' is more readable than 'maccatalyst'. I renamed the objdump output,
but the assembly should match it as well.
llvm-svn: 365964
Mac Catalyst is a new MachO platform in macOS Catalina.
It always uses the build_version MachO load command.
Differential Revision: https://reviews.llvm.org/D64107
llvm-svn: 364981
Summary:
These are output by clang -S, so can now be roundtripped thru clang.
(partially) fixes: https://bugs.llvm.org/show_bug.cgi?id=34544
Reviewers: dschuff
Subscribers: sbc100, jgravelle-google, aheejin, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63901
llvm-svn: 364658
llvm-mc or clang with -g normally produces debug info describing the
assembler source itself; however, if that source already contains some
.file/.loc directives, we should instead emit the debug info described
by those directives. For certain assembler sources seen in the wild
(particularly in the Chrome build) this was causing a crash due to
incorrect assumptions about legal sequences of assembler source text.
Fixes PR38994.
Differential Revision: https://reviews.llvm.org/D63573
llvm-svn: 364039
This provides the correct file path for the original source, rather
than the preprocessed source.
Part of the fix for PR41839.
Differential Revision: https://reviews.llvm.org/D62074
llvm-svn: 361248
This patch implements a limited form of autolinking primarily designed to allow
either the --dependent-library compiler option, or "comment lib" pragmas (
https://docs.microsoft.com/en-us/cpp/preprocessor/comment-c-cpp?view=vs-2017) in
C/C++ e.g. #pragma comment(lib, "foo"), to cause an ELF linker to automatically
add the specified library to the link when processing the input file generated
by the compiler.
Currently this extension is unique to LLVM and LLD. However, care has been taken
to design this feature so that it could be supported by other ELF linkers.
The design goals were to provide:
- A simple linking model for developers to reason about.
- The ability to to override autolinking from the linker command line.
- Source code compatibility, where possible, with "comment lib" pragmas in other
environments (MSVC in particular).
Dependent library support is implemented differently for ELF platforms than on
the other platforms. Primarily this difference is that on ELF we pass the
dependent library specifiers directly to the linker without manipulating them.
This is in contrast to other platforms where they are mapped to a specific
linker option by the compiler. This difference is a result of the greater
variety of ELF linkers and the fact that ELF linkers tend to handle libraries in
a more complicated fashion than on other platforms. This forces us to defer
handling the specifiers to the linker.
In order to achieve a level of source code compatibility with other platforms
we have restricted this feature to work with libraries that meet the following
"reasonable" requirements:
1. There are no competing defined symbols in a given set of libraries, or
if they exist, the program owner doesn't care which is linked to their
program.
2. There may be circular dependencies between libraries.
The binary representation is a mergeable string section (SHF_MERGE,
SHF_STRINGS), called .deplibs, with custom type SHT_LLVM_DEPENDENT_LIBRARIES
(0x6fff4c04). The compiler forms this section by concatenating the arguments of
the "comment lib" pragmas and --dependent-library options in the order they are
encountered. Partial (-r, -Ur) links are handled by concatenating .deplibs
sections with the normal mergeable string section rules. As an example, #pragma
comment(lib, "foo") would result in:
.section ".deplibs","MS",@llvm_dependent_libraries,1
.asciz "foo"
For LTO, equivalent information to the contents of a the .deplibs section can be
retrieved by the LLD for bitcode input files.
LLD processes the dependent library specifiers in the following way:
1. Dependent libraries which are found from the specifiers in .deplibs sections
of relocatable object files are added when the linker decides to include that
file (which could itself be in a library) in the link. Dependent libraries
behave as if they were appended to the command line after all other options. As
a consequence the set of dependent libraries are searched last to resolve
symbols.
2. It is an error if a file cannot be found for a given specifier.
3. Any command line options in effect at the end of the command line parsing apply
to the dependent libraries, e.g. --whole-archive.
4. The linker tries to add a library or relocatable object file from each of the
strings in a .deplibs section by; first, handling the string as if it was
specified on the command line; second, by looking for the string in each of the
library search paths in turn; third, by looking for a lib<string>.a or
lib<string>.so (depending on the current mode of the linker) in each of the
library search paths.
5. A new command line option --no-dependent-libraries tells LLD to ignore the
dependent libraries.
Rationale for the above points:
1. Adding the dependent libraries last makes the process simple to understand
from a developers perspective. All linkers are able to implement this scheme.
2. Error-ing for libraries that are not found seems like better behavior than
failing the link during symbol resolution.
3. It seems useful for the user to be able to apply command line options which
will affect all of the dependent libraries. There is a potential problem of
surprise for developers, who might not realize that these options would apply
to these "invisible" input files; however, despite the potential for surprise,
this is easy for developers to reason about and gives developers the control
that they may require.
4. This algorithm takes into account all of the different ways that ELF linkers
find input files. The different search methods are tried by the linker in most
obvious to least obvious order.
5. I considered adding finer grained control over which dependent libraries were
ignored (e.g. MSVC has /nodefaultlib:<library>); however, I concluded that this
is not necessary: if finer control is required developers can fall back to using
the command line directly.
RFC thread: http://lists.llvm.org/pipermail/llvm-dev/2019-March/131004.html.
Differential Revision: https://reviews.llvm.org/D60274
llvm-svn: 360984
Eric Astor