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Compute program header flags in rewriteSectionsLibrary #467

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Compute program header flags in rewriteSectionsLibrary #467

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4b1c228
rewriteSectionsLibrary cleanup
cgzones Feb 22, 2023
9bf837c
Compute program header flags in rewriteSectionsLibrary
cgzones Feb 22, 2023
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20 changes: 14 additions & 6 deletions src/patchelf.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -787,24 +787,22 @@ void ElfFile<ElfFileParamNames>::rewriteSectionsLibrary()
/* When normalizing note segments we will in the worst case be adding
1 program header for each SHT_NOTE section. */
unsigned int num_notes = std::count_if(shdrs.begin(), shdrs.end(),
[this](Elf_Shdr shdr) { return rdi(shdr.sh_type) == SHT_NOTE; });
[this](const Elf_Shdr & shdr) { return rdi(shdr.sh_type) == SHT_NOTE; });

/* Because we're adding a new section header, we're necessarily increasing
the size of the program header table. This can cause the first section
to overlap the program header table in memory; we need to shift the first
few segments to someplace else. */
/* Some sections may already be replaced so account for that */
unsigned int i = 1;
Elf_Addr pht_size = sizeof(Elf_Ehdr) + (phdrs.size() + num_notes + 1)*sizeof(Elf_Phdr);
while( i < rdi(hdr()->e_shnum) && rdi(shdrs.at(i).sh_offset) <= pht_size ) {
for (unsigned int i = 1; i < rdi(hdr()->e_shnum) && rdi(shdrs.at(i).sh_offset) <= pht_size; i++) {
if (not haveReplacedSection(getSectionName(shdrs.at(i))))
replaceSection(getSectionName(shdrs.at(i)), rdi(shdrs.at(i).sh_size));
i++;
}

/* Compute the total space needed for the replaced sections */
off_t neededSpace = 0;
for (auto & s : replacedSections)
for (const auto & s : replacedSections)
neededSpace += roundUp(s.second.size(), sectionAlignment);
debug("needed space is %d\n", neededSpace);

Expand Down Expand Up @@ -844,7 +842,17 @@ void ElfFile<ElfFileParamNames>::rewriteSectionsLibrary()
wri(phdr.p_offset, startOffset);
wri(phdr.p_vaddr, wri(phdr.p_paddr, startPage));
wri(phdr.p_filesz, wri(phdr.p_memsz, neededSpace));
wri(phdr.p_flags, PF_R | PF_W);
{
bool need_write = false, need_exec = false;
for (const auto & rs : replacedSections) {
const auto flags = findSectionHeader(rs.first).sh_flags;
if (flags & SHF_WRITE)
need_write = true;
if (flags & SHF_EXECINSTR)
need_exec = true;
}
wri(phdr.p_flags, PF_R | (need_write ? PF_W : 0) | (need_exec ? PF_X : 0));
Comment on lines +847 to +854
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Another way to write this would be:

auto flagUnion = PF_R;
for (const auto& rs : replacedSections) {
    const auto flags = findSectionHeader(rs.first).sh_flags;
    flagUnion |= (flags & SHF_WRITE) ? PF_W : 0;
    flagUnion |= (flags & SHF_EXECINSTR) ? PF_X : 0;
}
wri(phdr.p_flags, flagUnion);

But that's style, feel free to drop.

}
wri(phdr.p_align, getPageSize());


Expand Down