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Fix comments again. 

I thought I fixed the page size, but there were still errors.
This patch also contains fixes for grammatical errors.
Thanks pcc for proofreading!

llvm-svn: 301454
This commit is contained in:
Rui Ueyama 2017-04-26 20:20:05 +00:00
parent 370296302d
commit 0417172387
1 changed files with 21 additions and 24 deletions
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45
lld/COFF/Chunks.cpp
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@ -326,40 +326,37 @@ void SEHTableChunk::writeTo(uint8_t *Buf) const {
// usually loaded to that address. However, if there's already another
// DLL that overlaps, the loader has to relocate it. To do that, DLLs
// contain .reloc sections which contain offsets that need to be fixed
// up at runtime. If the loader find that a DLL cannot be loaded to its
// up at runtime. If the loader finds that a DLL cannot be loaded to its
// desired base address, it loads it to somewhere else, and add <actual
// base address> - <desired base address> to each offset that is
// specified by .reloc section.
// specified by the .reloc section. In ELF terms, .reloc sections
// contain relative relocations in REL format (as opposed to RELA.)
//
// In ELF terms, .reloc sections contain arrays of relocation offsets.
// All these offsets in the section are implicitly R_*_RELATIVE, and
// addends are read from section contents (so it is REL as opposed to
// RELA).
// This already significantly reduces the size of relocations compared
// to ELF .rel.dyn, but Windows does more to reduce it (probably because
// it was invented for PCs in the late '80s or early '90s.) Offsets in
// .reloc are grouped by page where the page size is 12 bits, and
// offsets sharing the same page address are stored consecutively to
// represent them with less space. This is very similar to the page
// table which is grouped by (multiple stages of) pages.
//
// This already reduce the size of relocations to 1/3 compared to ELF
// .dynrel, but Windows does more to reduce it (probably because it was
// invented for PCs in the late '80s or early '90s.) Offsets in .reloc
// are grouped by page where page size is 20 bits, and offsets sharing
// the same page address are stored consecutively to represent them with
// less space. This is a very similar to the page table which is grouped
// by (multiple stages of) pages.
//
// For example, let's say we have 0x00030, 0x00500, 0x01000, 0x01100,
// 0x20004, and 0x20008 in a .reloc section. In the section, they are
// represented like this:
// For example, let's say we have 0x00030, 0x00500, 0x00700, 0x00A00,
// 0x20004, and 0x20008 in a .reloc section for x64. The uppermost 4
// bits have a type IMAGE_REL_BASED_DIR64 or 0xA. In the section, they
// are represented like this:
//
// 0x00000 -- page address (4 bytes)
// 16 -- size of this block (4 bytes)
// 0x0030 -- entries (2 bytes each)
// 0x0500
// 0x1000
// 0x1100
// 0xA030 -- entries (2 bytes each)
// 0xA500
// 0xA700
// 0xAA00
// 0x20000 -- page address (4 bytes)
// 12 -- size of this block (4 bytes)
// 0x0004 -- entries (2 bytes each)
// 0x0008
// 0xA004 -- entries (2 bytes each)
// 0xA008
//
// Usually we have a lot of relocatinos for each page, so the number of
// Usually we have a lot of relocations for each page, so the number of
// bytes for one .reloc entry is close to 2 bytes on average.
BaserelChunk::BaserelChunk(uint32_t Page, Baserel *Begin, Baserel *End) {
// Block header consists of 4 byte page RVA and 4 byte block size.