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Kernel+LibELF: Support initializing values of TLS data

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Previously, TLS data was always zero-initialized.

To support initializing the values of TLS data, sys$allocate_tls now
receives a buffer with the desired initial data, and copies it to the
master TLS region of the process.

The DynamicLinker gathers the initial TLS image and passes it to
sys$allocate_tls.

We also now require the size passed to sys$allocate_tls to be
page-aligned, to make things easier. Note that this doesn't waste memory
as the TLS data has to be allocated in separate pages anyway.
This commit is contained in:
Itamar 2021-04-24 11:30:20 +03:00 • committed by Andreas Kling
parent db76702d71
commit 6bbd2ebf83
7 changed files with 63 additions and 12 deletions
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30
Userland/Libraries/LibELF/DynamicLoader.cpp
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@ -495,6 +495,36 @@ ssize_t DynamicLoader::negative_offset_from_tls_block_end(size_t value_of_symbol
return negative_offset;
}
void DynamicLoader::copy_initial_tls_data_into(ByteBuffer& buffer, size_t total_tls_size) const
{
const u8* tls_data = nullptr;
size_t tls_size_in_image = 0;
m_elf_image.for_each_program_header([this, &tls_data, &tls_size_in_image](ELF::Image::ProgramHeader program_header) {
if (program_header.type() != PT_TLS)
return IterationDecision::Continue;
tls_data = (const u8*)m_file_data + program_header.offset();
tls_size_in_image = program_header.size_in_image();
return IterationDecision::Break;
});
if (!tls_data || !tls_size_in_image)
return;
m_elf_image.for_each_symbol([this, &buffer, total_tls_size, tls_data](ELF::Image::Symbol symbol) {
if (symbol.type() != STT_TLS)
return IterationDecision::Continue;
ssize_t negative_offset = negative_offset_from_tls_block_end(symbol.value(), m_tls_offset, total_tls_size);
VERIFY(symbol.size() != 0);
VERIFY(buffer.size() + negative_offset + symbol.size() <= buffer.size());
memcpy(buffer.data() + buffer.size() + negative_offset, tls_data + symbol.value(), symbol.size());
return IterationDecision::Continue;
});
}
// Defined in <arch>/plt_trampoline.S
extern "C" void _plt_trampoline(void) __attribute__((visibility("hidden")));