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DynamicLoader: Only remap text segments private if there are textrels

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We now map most shared library text segments shared, read+exec only.
This reduces our memory footprint at system startup by 16 MB which is
pretty neat! :^)
This commit is contained in:
Andreas Kling 2020-12-29 02:13:26 +01:00
parent 30dbe9c78a
commit 572d3bb0b8
1 changed files with 11 additions and 1 deletions
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12
Libraries/LibELF/DynamicLoader.cpp
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@ -184,6 +184,13 @@ bool DynamicLoader::load_stage_2(unsigned flags, size_t total_tls_size)
if (m_dynamic_object->has_text_relocations()) {
// dbg() << "Someone linked non -fPIC code into " << m_filename << " :(";
ASSERT(m_text_segment_load_address.get() != 0);
// Remap this text region as private.
if (mremap(m_text_segment_load_address.as_ptr(), m_text_segment_size, m_text_segment_size, MAP_PRIVATE) == MAP_FAILED) {
perror("mremap .text: MAP_PRIVATE");
return false;
}
if (0 > mprotect(m_text_segment_load_address.as_ptr(), m_text_segment_size, PROT_READ | PROT_WRITE)) {
perror("mprotect .text: PROT_READ | PROT_WRITE"); // FIXME: dlerror?
return false;
@ -242,11 +249,14 @@ void DynamicLoader::load_program_headers()
// Process regions in order: .text, .data, .tls
auto* region = text_region_ptr;
void* requested_load_address = m_elf_image.is_dynamic() ? nullptr : region->desired_load_address().as_ptr();
ASSERT(!region->is_writable());
void* text_segment_begin = mmap_with_name(
requested_load_address,
region->required_load_size(),
region->mmap_prot(),
MAP_PRIVATE,
MAP_SHARED,
m_image_fd,
region->offset(),
String::format("%s: .text", m_filename.characters()).characters());