diff options
| -rw-r--r-- | subx/021translate.cc | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/subx/021translate.cc b/subx/021translate.cc index 636ce607..7fdeb93c 100644 --- a/subx/021translate.cc +++ b/subx/021translate.cc @@ -101,12 +101,20 @@ void dump_elf_header(ostream& out, const program& p) { // p_flags uint32_t p_flags = (i == 0) ? /*r-x*/0x5 : /*rw-*/0x6; // convention: only first segment is code emit(p_flags); + // p_align - // "The value of the p_align field of each program header in a shared - // object file must be a multiple of the system page size." -- http://refspecs.linuxfoundation.org/ELF/zSeries/lzsabi0_zSeries/c2083.html + // "As the system creates or augments a process image, it logically copies + // a file's segment to a virtual memory segment. When—and if— the system + // physically reads the file depends on the program's execution behavior, + // system load, and so on. A process does not require a physical page + // unless it references the logical page during execution, and processes + // commonly leave many pages unreferenced. Therefore delaying physical + // reads frequently obviates them, improving system performance. To obtain + // this efficiency in practice, executable and shared object files must + // have segment images whose file offsets and virtual addresses are + // congruent, modulo the page size." -- http://refspecs.linuxbase.org/elf/elf.pdf (page 95) uint32_t p_align = 0x1000; emit(p_align); - if (p_offset % p_align != p.segments.at(i).start % p_align) { raise << "segment starting at 0x" << HEXWORD << p.segments.at(i).start << " is improperly aligned; alignment for p_offset " << p_offset << " should be " << (p_offset % p_align) << " but is " << (p.segments.at(i).start % p_align) << '\n' << end(); return; |