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Improve the performance of detecting linux-musl platform by parsing ELF
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Original file line number | Diff line number | Diff line change |
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// Copyright 2024 Google LLC. Use of this source code is governed by an | ||
// MIT-style license that can be found in the LICENSE file or at | ||
// https://opensource.org/licenses/MIT. | ||
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import * as fs from 'fs'; | ||
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/** | ||
* Read chunk of data from a file descriptor into a new Buffer. | ||
*/ | ||
const readFileDescriptor = function ( | ||
fd: number, | ||
position: number, | ||
length: number | ||
): Buffer { | ||
const buffer = Buffer.alloc(length); | ||
let offset = 0; | ||
while (offset < length) { | ||
const bytesRead = fs.readSync(fd, buffer, { | ||
offset: offset, | ||
position: position + offset, | ||
}); | ||
if (bytesRead === 0) { | ||
throw new Error(`failed to read fd ${fd}`); | ||
} | ||
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offset += bytesRead; | ||
} | ||
return buffer; | ||
}; | ||
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/** | ||
* Parse an ELF file and return its interpreter. | ||
*/ | ||
export const getELFInterpreter = function (path: string): string { | ||
const fd = fs.openSync(path, 'r'); | ||
try { | ||
const eIdent = new DataView(readFileDescriptor(fd, 0, 64).buffer); | ||
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if ( | ||
eIdent.getUint8(0) !== 0x7f || | ||
eIdent.getUint8(1) !== 0x45 || | ||
eIdent.getUint8(2) !== 0x4c || | ||
eIdent.getUint8(3) !== 0x46 | ||
) { | ||
throw new Error(`${path} is not an elf file.`); | ||
} | ||
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const eIdentClass = eIdent.getUint8(4); | ||
if (eIdentClass !== 1 && eIdentClass !== 2) { | ||
throw new Error(`${path} has an invalid elf class.`); | ||
} | ||
const class32 = eIdentClass === 1; | ||
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const eIdentData = eIdent.getUint8(5); | ||
if (eIdentData !== 1 && eIdentData !== 2) { | ||
throw new Error(`${path} has an invalid endianness.`); | ||
} | ||
const littleEndian = eIdentData === 1; | ||
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const e_phoff = class32 | ||
? eIdent.getUint32(28, littleEndian) | ||
: Number(eIdent.getBigUint64(32, littleEndian)); | ||
const e_phentsize = class32 | ||
? eIdent.getUint16(42, littleEndian) | ||
: eIdent.getUint16(54, littleEndian); | ||
const e_phnum = class32 | ||
? eIdent.getUint16(44, littleEndian) | ||
: eIdent.getUint16(56, littleEndian); | ||
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const proghdrs = new DataView( | ||
readFileDescriptor(fd, e_phoff, e_phentsize * e_phnum).buffer | ||
); | ||
for (let i = 0; i < e_phnum; i++) { | ||
const byteOffset = i * e_phentsize; | ||
const p_type = proghdrs.getUint32(byteOffset, littleEndian); | ||
if (p_type !== 3) { | ||
continue; | ||
} | ||
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const p_offset = class32 | ||
? proghdrs.getUint32(byteOffset + 4, littleEndian) | ||
: Number(proghdrs.getBigUint64(byteOffset + 8, littleEndian)); | ||
const p_filesz = class32 | ||
? proghdrs.getUint32(byteOffset + 16, littleEndian) | ||
: Number(proghdrs.getBigUint64(byteOffset + 32, littleEndian)); | ||
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const buffer = readFileDescriptor(fd, p_offset, p_filesz); | ||
if (buffer[p_filesz - 1] !== 0) { | ||
throw new Error(`${path} is corrupted.`); | ||
} | ||
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return buffer.toString('utf8', 0, p_filesz - 1); | ||
} | ||
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throw new Error(`${path} does not contain an interpreter entry.`); | ||
} finally { | ||
fs.closeSync(fd); | ||
} | ||
}; |