[llvm] 85f4023 - [COFF] Move section name encoding into BinaryFormat
Martin Storsjö via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 21 03:51:30 PST 2022
Author: Nicolas Miller
Date: 2022-02-21T13:50:56+02:00
New Revision: 85f4023e731c0c42e45bf32bfcbf5f73c2013384
URL: https://github.com/llvm/llvm-project/commit/85f4023e731c0c42e45bf32bfcbf5f73c2013384
DIFF: https://github.com/llvm/llvm-project/commit/85f4023e731c0c42e45bf32bfcbf5f73c2013384.diff
LOG: [COFF] Move section name encoding into BinaryFormat
Large COFF section names are moved into the string table and the
section header field is the offset into the string table encoded in
ASCII for offset smaller than 7 digits and in base64 for larger
offsets.
The operation of taking the string table offsets is done in a few
places in the codebase, so it is helpful to move this operation into
`BinaryFormat` so that it can be shared everywhere it's done.
So this patch takes the implementation of this operation from
`llvm/lib/MC/WinCOFFObjectWriter.cpp` and moves it into `BinaryFormat`.
Reviewed By: jhenderson, rnk
Differential Revision: https://reviews.llvm.org/D118793
Added:
llvm/lib/BinaryFormat/COFF.cpp
Modified:
llvm/include/llvm/BinaryFormat/COFF.h
llvm/lib/BinaryFormat/CMakeLists.txt
llvm/lib/MC/WinCOFFObjectWriter.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/BinaryFormat/COFF.h b/llvm/include/llvm/BinaryFormat/COFF.h
index e7dde986784f7..016fe02894065 100644
--- a/llvm/include/llvm/BinaryFormat/COFF.h
+++ b/llvm/include/llvm/BinaryFormat/COFF.h
@@ -731,6 +731,10 @@ inline bool isReservedSectionNumber(int32_t SectionNumber) {
return SectionNumber <= 0;
}
+/// Encode section name based on string table offset.
+/// The size of Out must be at least COFF::NameSize.
+bool encodeSectionName(char *Out, uint64_t Offset);
+
} // End namespace COFF.
} // End namespace llvm.
diff --git a/llvm/lib/BinaryFormat/CMakeLists.txt b/llvm/lib/BinaryFormat/CMakeLists.txt
index 37f6865a487e8..50c1713804368 100644
--- a/llvm/lib/BinaryFormat/CMakeLists.txt
+++ b/llvm/lib/BinaryFormat/CMakeLists.txt
@@ -1,5 +1,6 @@
add_llvm_component_library(LLVMBinaryFormat
AMDGPUMetadataVerifier.cpp
+ COFF.cpp
Dwarf.cpp
ELF.cpp
MachO.cpp
diff --git a/llvm/lib/BinaryFormat/COFF.cpp b/llvm/lib/BinaryFormat/COFF.cpp
new file mode 100644
index 0000000000000..8fbee0218b79b
--- /dev/null
+++ b/llvm/lib/BinaryFormat/COFF.cpp
@@ -0,0 +1,57 @@
+//===- llvm/BinaryFormat/COFF.cpp - The COFF format -----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/BinaryFormat/COFF.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Twine.h"
+
+// Maximum offsets for
diff erent string table entry encodings.
+enum : unsigned { Max7DecimalOffset = 9999999U };
+enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
+
+// Encode a string table entry offset in base 64, padded to 6 chars, and
+// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
+// Buffer must be at least 8 bytes large. No terminating null appended.
+static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
+ assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
+ "Illegal section name encoding for value");
+
+ static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+ "abcdefghijklmnopqrstuvwxyz"
+ "0123456789+/";
+
+ Buffer[0] = '/';
+ Buffer[1] = '/';
+
+ char *Ptr = Buffer + 7;
+ for (unsigned i = 0; i < 6; ++i) {
+ unsigned Rem = Value % 64;
+ Value /= 64;
+ *(Ptr--) = Alphabet[Rem];
+ }
+}
+
+bool llvm::COFF::encodeSectionName(char *Out, uint64_t Offset) {
+ if (Offset <= Max7DecimalOffset) {
+ // Offsets of 7 digits or less are encoded in ASCII.
+ SmallVector<char, COFF::NameSize> Buffer;
+ Twine('/').concat(Twine(Offset)).toVector(Buffer);
+ assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
+ std::memcpy(Out, Buffer.data(), Buffer.size());
+ return true;
+ }
+
+ if (Offset <= MaxBase64Offset) {
+ // Starting with 10,000,000, offsets are encoded as base64.
+ encodeBase64StringEntry(Out, Offset);
+ return true;
+ }
+
+ // The offset is too large to be encoded.
+ return false;
+}
diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index 0cbe51dfe3250..2af94b4f69a7b 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -451,32 +451,6 @@ void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &MCSym,
Sym->MC = &MCSym;
}
-// Maximum offsets for
diff erent string table entry encodings.
-enum : unsigned { Max7DecimalOffset = 9999999U };
-enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
-
-// Encode a string table entry offset in base 64, padded to 6 chars, and
-// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
-// Buffer must be at least 8 bytes large. No terminating null appended.
-static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
- assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
- "Illegal section name encoding for value");
-
- static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
- "abcdefghijklmnopqrstuvwxyz"
- "0123456789+/";
-
- Buffer[0] = '/';
- Buffer[1] = '/';
-
- char *Ptr = Buffer + 7;
- for (unsigned i = 0; i < 6; ++i) {
- unsigned Rem = Value % 64;
- Value /= 64;
- *(Ptr--) = Alphabet[Rem];
- }
-}
-
void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
if (S.Name.size() <= COFF::NameSize) {
std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
@@ -484,19 +458,8 @@ void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
}
uint64_t StringTableEntry = Strings.getOffset(S.Name);
- if (StringTableEntry <= Max7DecimalOffset) {
- SmallVector<char, COFF::NameSize> Buffer;
- Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
- assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
- std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
- return;
- }
- if (StringTableEntry <= MaxBase64Offset) {
- // Starting with 10,000,000, offsets are encoded as base64.
- encodeBase64StringEntry(S.Header.Name, StringTableEntry);
- return;
- }
- report_fatal_error("COFF string table is greater than 64 GB.");
+ if (!COFF::encodeSectionName(S.Header.Name, StringTableEntry))
+ report_fatal_error("COFF string table is greater than 64 GB.");
}
void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {
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