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[Support] Allow FileOutputBuffer::create to create an empty file

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Size==0 triggers `assert(Size != 0)` in mapped_file_region::init.
I plan to use an empty file in D79339 (llvm-objcopy --dump-section).

According to POSIX, "If len is zero, mmap() shall fail and no mapping
shall be established." Just specialize case Size=0 to use
createInMemoryBuffer.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D79338
This commit is contained in:
Fangrui Song 2020-05-04 09:45:41 -07:00
parent 41fde1024a
commit 8bc7bc4570
2 changed files with 19 additions and 0 deletions
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4
lib/Support/FileOutputBuffer.cpp
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@ -172,6 +172,10 @@ FileOutputBuffer::create(StringRef Path, size_t Size, unsigned Flags) {
if (Flags & F_executable)
Mode |= fs::all_exe;
// If Size is zero, don't use mmap which will fail with EINVAL.
if (Size == 0)
return createInMemoryBuffer(Path, Size, Mode);
fs::file_status Stat;
fs::status(Path, Stat);

15
unittests/Support/FileOutputBufferTest.cpp
View File

@ -140,6 +140,21 @@ TEST(FileOutputBuffer, Test) {
ASSERT_NO_ERROR(fs::file_size(Twine(File5), File5Size));
ASSERT_EQ(File5Size, 8000ULL);
ASSERT_NO_ERROR(fs::remove(File5.str()));
// TEST 6: Create an empty file.
SmallString<128> File6(TestDirectory);
File6.append("/file6");
{
Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
FileOutputBuffer::create(File6, 0);
ASSERT_NO_ERROR(errorToErrorCode(BufferOrErr.takeError()));
ASSERT_NO_ERROR(errorToErrorCode((*BufferOrErr)->commit()));
}
uint64_t File6Size;
ASSERT_NO_ERROR(fs::file_size(Twine(File6), File6Size));
ASSERT_EQ(File6Size, 0ULL);
ASSERT_NO_ERROR(fs::remove(File6.str()));
// Clean up.
ASSERT_NO_ERROR(fs::remove(TestDirectory.str()));
}