2009-08-13 13:07:35 +08:00
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//===- lib/MC/MCSectionELF.cpp - ELF Code Section Representation ----------===//
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//
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2019-01-19 16:50:56 +08:00
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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2009-08-13 13:07:35 +08:00
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//
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//===----------------------------------------------------------------------===//
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2017-06-06 19:49:48 +08:00
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#include "llvm/MC/MCSectionELF.h"
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2017-02-14 08:33:36 +08:00
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#include "llvm/ADT/Triple.h"
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2017-06-07 11:48:56 +08:00
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#include "llvm/BinaryFormat/ELF.h"
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2010-01-14 05:21:29 +08:00
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#include "llvm/MC/MCAsmInfo.h"
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2013-04-18 05:18:16 +08:00
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#include "llvm/MC/MCExpr.h"
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2017-03-10 16:22:13 +08:00
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#include "llvm/Support/ErrorHandling.h"
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2009-08-13 13:07:35 +08:00
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#include "llvm/Support/raw_ostream.h"
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2017-02-14 08:33:36 +08:00
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#include <cassert>
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2011-01-23 12:28:49 +08:00
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2009-08-13 13:07:35 +08:00
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using namespace llvm;
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2014-10-10 05:23:39 +08:00
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// Decides whether a '.section' directive
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// should be printed before the section name.
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2010-01-23 02:21:23 +08:00
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bool MCSectionELF::ShouldOmitSectionDirective(StringRef Name,
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2010-01-14 05:21:29 +08:00
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const MCAsmInfo &MAI) const {
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2015-04-05 02:02:01 +08:00
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if (isUnique())
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2015-02-18 04:48:01 +08:00
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return false;
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MCAsmInfo: Allow targets to specify when the .section directive should be omitted
Summary:
The default behavior is to omit the .section directive for .text, .data,
and sometimes .bss, but some targets may want to omit this directive for
other sections too.
The AMDGPU backend will uses this to emit a simplified syntax for section
switches. For example if the section directive is not omitted (current
behavior), section switches to .hsatext will be printed like this:
.section .hsatext,#alloc,#execinstr,#write
This is actually wrong, because .hsatext has some custom STT_* flags,
which MC doesn't know how to print or parse.
If the section directive is omitted (made possible by this commit),
section switches will be printed like this:
.hsatext
The motivation for this patch is to make it possible to emit sections
with custom STT_* flags without having to teach MC about all the target
specific STT_* flags.
Reviewers: rafael, grosbach
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D12423
llvm-svn: 248618
2015-09-26 05:41:14 +08:00
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return MAI.shouldOmitSectionDirective(Name);
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2009-08-13 13:07:35 +08:00
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}
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2013-11-13 22:01:59 +08:00
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static void printName(raw_ostream &OS, StringRef Name) {
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if (Name.find_first_not_of("0123456789_."
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"abcdefghijklmnopqrstuvwxyz"
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"ABCDEFGHIJKLMNOPQRSTUVWXYZ") == Name.npos) {
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OS << Name;
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return;
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}
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OS << '"';
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for (const char *B = Name.begin(), *E = Name.end(); B < E; ++B) {
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if (*B == '"') // Unquoted "
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OS << "\\\"";
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else if (*B != '\\') // Neither " or backslash
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OS << *B;
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else if (B + 1 == E) // Trailing backslash
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OS << "\\\\";
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else {
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OS << B[0] << B[1]; // Quoted character
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++B;
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}
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}
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OS << '"';
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}
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2017-01-30 23:38:43 +08:00
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void MCSectionELF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
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2013-04-18 05:18:16 +08:00
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raw_ostream &OS,
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const MCExpr *Subsection) const {
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2020-04-16 06:49:05 +08:00
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if (ShouldOmitSectionDirective(getName(), MAI)) {
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2020-04-16 06:49:05 +08:00
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OS << '\t' << getName();
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2015-06-09 08:31:39 +08:00
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if (Subsection) {
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OS << '\t';
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Subsection->print(OS, &MAI);
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}
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2013-04-18 05:18:16 +08:00
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OS << '\n';
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2009-08-13 13:07:35 +08:00
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return;
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}
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2013-11-13 22:01:59 +08:00
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OS << "\t.section\t";
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2020-04-16 06:49:05 +08:00
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printName(OS, getName());
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2011-03-04 06:31:08 +08:00
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2009-08-13 13:07:35 +08:00
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// Handle the weird solaris syntax if desired.
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2012-05-11 09:41:30 +08:00
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if (MAI.usesSunStyleELFSectionSwitchSyntax() &&
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2011-01-23 12:43:11 +08:00
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!(Flags & ELF::SHF_MERGE)) {
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if (Flags & ELF::SHF_ALLOC)
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2009-08-13 13:07:35 +08:00
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OS << ",#alloc";
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_EXECINSTR)
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2009-08-13 13:07:35 +08:00
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OS << ",#execinstr";
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_WRITE)
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2009-08-13 13:07:35 +08:00
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OS << ",#write";
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2013-09-16 03:53:20 +08:00
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if (Flags & ELF::SHF_EXCLUDE)
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OS << ",#exclude";
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_TLS)
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2009-08-13 13:07:35 +08:00
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OS << ",#tls";
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2010-04-09 05:26:26 +08:00
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OS << '\n';
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return;
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}
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2012-05-11 09:41:30 +08:00
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2010-04-09 05:26:26 +08:00
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OS << ",\"";
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_ALLOC)
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2010-04-09 05:26:26 +08:00
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OS << 'a';
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2013-09-16 03:53:20 +08:00
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if (Flags & ELF::SHF_EXCLUDE)
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OS << 'e';
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_EXECINSTR)
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2010-04-09 05:26:26 +08:00
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OS << 'x';
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2011-02-15 06:23:49 +08:00
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if (Flags & ELF::SHF_GROUP)
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OS << 'G';
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_WRITE)
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2010-04-09 05:26:26 +08:00
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OS << 'w';
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_MERGE)
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2010-04-09 05:26:26 +08:00
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OS << 'M';
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_STRINGS)
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2010-04-09 05:26:26 +08:00
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OS << 'S';
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2011-01-23 12:43:11 +08:00
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if (Flags & ELF::SHF_TLS)
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2010-04-09 05:26:26 +08:00
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OS << 'T';
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2017-03-15 03:28:51 +08:00
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if (Flags & ELF::SHF_LINK_ORDER)
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2017-04-05 06:35:08 +08:00
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OS << 'o';
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2021-02-03 01:34:08 +08:00
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if (Flags & ELF::SHF_GNU_RETAIN)
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OS << 'R';
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2012-05-11 09:41:30 +08:00
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2010-04-09 05:26:26 +08:00
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// If there are target-specific flags, print them.
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2017-01-30 23:38:43 +08:00
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Triple::ArchType Arch = T.getArch();
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if (Arch == Triple::xcore) {
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if (Flags & ELF::XCORE_SHF_CP_SECTION)
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OS << 'c';
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if (Flags & ELF::XCORE_SHF_DP_SECTION)
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OS << 'd';
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2017-08-13 01:40:18 +08:00
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} else if (T.isARM() || T.isThumb()) {
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2017-01-30 23:38:43 +08:00
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if (Flags & ELF::SHF_ARM_PURECODE)
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OS << 'y';
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2018-11-09 22:17:27 +08:00
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} else if (Arch == Triple::hexagon) {
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if (Flags & ELF::SHF_HEX_GPREL)
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OS << 's';
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2017-01-30 23:38:43 +08:00
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}
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2012-05-11 09:41:30 +08:00
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2010-04-09 05:26:26 +08:00
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OS << '"';
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2009-08-13 13:07:35 +08:00
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2010-11-10 07:42:07 +08:00
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OS << ',';
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// If comment string is '@', e.g. as on ARM - use '%' instead
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if (MAI.getCommentString()[0] == '@')
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OS << '%';
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else
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OS << '@';
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2011-01-23 12:28:49 +08:00
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if (Type == ELF::SHT_INIT_ARRAY)
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2010-11-10 07:42:07 +08:00
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OS << "init_array";
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2011-01-23 12:28:49 +08:00
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else if (Type == ELF::SHT_FINI_ARRAY)
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2010-11-10 07:42:07 +08:00
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OS << "fini_array";
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2011-01-23 12:28:49 +08:00
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else if (Type == ELF::SHT_PREINIT_ARRAY)
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2010-11-10 07:42:07 +08:00
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OS << "preinit_array";
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2011-01-23 12:28:49 +08:00
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else if (Type == ELF::SHT_NOBITS)
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2010-11-10 07:42:07 +08:00
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OS << "nobits";
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2011-01-23 12:28:49 +08:00
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else if (Type == ELF::SHT_NOTE)
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2010-12-27 05:30:59 +08:00
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OS << "note";
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2011-01-23 12:28:49 +08:00
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else if (Type == ELF::SHT_PROGBITS)
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2010-11-10 07:42:07 +08:00
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OS << "progbits";
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2015-11-06 23:30:45 +08:00
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else if (Type == ELF::SHT_X86_64_UNWIND)
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OS << "unwind";
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2017-03-10 16:22:20 +08:00
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else if (Type == ELF::SHT_MIPS_DWARF)
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// Print hex value of the flag while we do not have
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// any standard symbolic representation of the flag.
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OS << "0x7000001e";
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2017-06-15 02:52:12 +08:00
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else if (Type == ELF::SHT_LLVM_ODRTAB)
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OS << "llvm_odrtab";
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2018-01-31 00:29:29 +08:00
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else if (Type == ELF::SHT_LLVM_LINKER_OPTIONS)
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OS << "llvm_linker_options";
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[MC] Add assembler support for .cg_profile.
Object FIle Representation
At codegen time this is emitted into the ELF file a pair of symbol indices and a weight. In assembly it looks like:
.cg_profile a, b, 32
.cg_profile freq, a, 11
.cg_profile freq, b, 20
When writing an ELF file these are put into a SHT_LLVM_CALL_GRAPH_PROFILE (0x6fff4c02) section as (uint32_t, uint32_t, uint64_t) tuples as (from symbol index, to symbol index, weight).
Differential Revision: https://reviews.llvm.org/D44965
llvm-svn: 333823
2018-06-03 00:33:01 +08:00
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else if (Type == ELF::SHT_LLVM_CALL_GRAPH_PROFILE)
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OS << "llvm_call_graph_profile";
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[ELF] Implement Dependent Libraries Feature
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
2019-05-17 11:44:15 +08:00
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else if (Type == ELF::SHT_LLVM_DEPENDENT_LIBRARIES)
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OS << "llvm_dependent_libraries";
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2019-05-29 11:29:01 +08:00
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else if (Type == ELF::SHT_LLVM_SYMPART)
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OS << "llvm_sympart";
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2020-10-09 02:12:40 +08:00
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else if (Type == ELF::SHT_LLVM_BB_ADDR_MAP)
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OS << "llvm_bb_addr_map";
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2017-03-10 16:22:13 +08:00
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else
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report_fatal_error("unsupported type 0x" + Twine::utohexstr(Type) +
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2020-04-16 06:49:05 +08:00
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" for section " + getName());
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2010-11-10 07:42:07 +08:00
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if (EntrySize) {
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2011-01-23 12:43:11 +08:00
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assert(Flags & ELF::SHF_MERGE);
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2010-11-10 07:42:07 +08:00
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OS << "," << EntrySize;
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2009-08-13 13:07:35 +08:00
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}
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2010-11-10 07:42:07 +08:00
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2013-11-13 22:01:59 +08:00
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if (Flags & ELF::SHF_GROUP) {
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OS << ",";
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2021-02-01 14:42:35 +08:00
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printName(OS, Group.getPointer()->getName());
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if (isComdat())
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OS << ",comdat";
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2013-11-13 22:01:59 +08:00
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}
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2015-02-18 04:48:01 +08:00
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2017-03-15 03:28:51 +08:00
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if (Flags & ELF::SHF_LINK_ORDER) {
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OS << ",";
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2020-08-04 04:35:59 +08:00
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if (LinkedToSym)
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printName(OS, LinkedToSym->getName());
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else
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OS << '0';
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2017-03-15 03:28:51 +08:00
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}
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2015-04-05 02:02:01 +08:00
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if (isUnique())
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2015-04-07 00:34:41 +08:00
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OS << ",unique," << UniqueID;
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2015-02-18 04:48:01 +08:00
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2009-08-13 13:07:35 +08:00
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OS << '\n';
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2013-04-18 05:18:16 +08:00
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2015-06-09 08:31:39 +08:00
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if (Subsection) {
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OS << "\t.subsection\t";
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Subsection->print(OS, &MAI);
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OS << '\n';
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}
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2009-08-13 13:07:35 +08:00
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}
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2010-10-05 01:32:41 +08:00
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bool MCSectionELF::UseCodeAlign() const {
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2011-01-23 12:43:11 +08:00
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return getFlags() & ELF::SHF_EXECINSTR;
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2010-10-05 01:32:41 +08:00
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}
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2010-11-18 04:03:54 +08:00
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bool MCSectionELF::isVirtualSection() const {
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2011-01-23 12:28:49 +08:00
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return getType() == ELF::SHT_NOBITS;
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2010-11-18 04:03:54 +08:00
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}
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2020-04-15 02:05:21 +08:00
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StringRef MCSectionELF::getVirtualSectionKind() const { return "SHT_NOBITS"; }
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