From 8998c55ec071ae36f2d32c8852a945f032239c4c Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Fri, 4 May 2018 14:55:31 -0400 Subject: [PATCH] cmd/link: separate virtual address layout from file layout Currently these two forms of layout are done in a single pass. This makes it difficult to compress DWARF sections because that must be done after relocations are applied, which must happen after virtual address layout, but we can't layout the file until we've compressed the DWARF sections. Fix this by separating the two layout steps. In the process, we can also unify the copy-pasted code in Link.address to compute file offsets, which currently has some unnecessary variation. Unlike the current file offset computation, which depends on virtual addresses, the new computation only uses file offsets and sizes. This will let us compress the file representation of a segment and create the file layout based on its on-disk size rather than its original in-memory size. Tested by comparing the test binary for the "strings" package on all supported GOOS/GOARCH combinations. All binaries are identical (except, of course, their build IDs). This is a second attempt at CL 111682. For #11799. Fixes #25863. Change-Id: If09f28771bb4d78dd392fd58b8d7c9d5f22b0b9e Reviewed-on: https://go-review.googlesource.com/118716 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Heschi Kreinick Reviewed-by: Ian Lance Taylor --- src/cmd/link/internal/ld/data.go | 75 ++++++++++++++++++++------------ src/cmd/link/internal/ld/main.go | 3 +- 2 files changed, 49 insertions(+), 29 deletions(-) diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go index 3e4773102d3..e3587345263 100644 --- a/src/cmd/link/internal/ld/data.go +++ b/src/cmd/link/internal/ld/data.go @@ -1903,12 +1903,15 @@ func assignAddress(ctxt *Link, sect *sym.Section, n int, s *sym.Symbol, va uint6 return sect, n, va } -// assign addresses -func (ctxt *Link) address() { +// address assigns virtual addresses to all segments and sections and +// returns all segments in file order. +func (ctxt *Link) address() []*sym.Segment { + var order []*sym.Segment // Layout order + va := uint64(*FlagTextAddr) + order = append(order, &Segtext) Segtext.Rwx = 05 Segtext.Vaddr = va - Segtext.Fileoff = uint64(HEADR) for _, s := range Segtext.Sections { va = uint64(Rnd(int64(va), int64(s.Align))) s.Vaddr = va @@ -1916,7 +1919,6 @@ func (ctxt *Link) address() { } Segtext.Length = va - uint64(*FlagTextAddr) - Segtext.Filelen = Segtext.Length if ctxt.HeadType == objabi.Hnacl { va += 32 // room for the "halt sled" } @@ -1937,13 +1939,9 @@ func (ctxt *Link) address() { // writable even for this short period. va = uint64(Rnd(int64(va), int64(*FlagRound))) + order = append(order, &Segrodata) Segrodata.Rwx = 04 Segrodata.Vaddr = va - Segrodata.Fileoff = va - Segtext.Vaddr + Segtext.Fileoff - Segrodata.Filelen = 0 - if ctxt.HeadType == objabi.Hwindows { - Segrodata.Fileoff = Segtext.Fileoff + uint64(Rnd(int64(Segtext.Length), PEFILEALIGN)) - } for _, s := range Segrodata.Sections { va = uint64(Rnd(int64(va), int64(s.Align))) s.Vaddr = va @@ -1951,17 +1949,15 @@ func (ctxt *Link) address() { } Segrodata.Length = va - Segrodata.Vaddr - Segrodata.Filelen = Segrodata.Length } if len(Segrelrodata.Sections) > 0 { // align to page boundary so as not to mix // rodata, rel-ro data, and executable text. va = uint64(Rnd(int64(va), int64(*FlagRound))) + order = append(order, &Segrelrodata) Segrelrodata.Rwx = 06 Segrelrodata.Vaddr = va - Segrelrodata.Fileoff = va - Segrodata.Vaddr + Segrodata.Fileoff - Segrelrodata.Filelen = 0 for _, s := range Segrelrodata.Sections { va = uint64(Rnd(int64(va), int64(s.Align))) s.Vaddr = va @@ -1969,20 +1965,12 @@ func (ctxt *Link) address() { } Segrelrodata.Length = va - Segrelrodata.Vaddr - Segrelrodata.Filelen = Segrelrodata.Length } va = uint64(Rnd(int64(va), int64(*FlagRound))) + order = append(order, &Segdata) Segdata.Rwx = 06 Segdata.Vaddr = va - Segdata.Fileoff = va - Segtext.Vaddr + Segtext.Fileoff - Segdata.Filelen = 0 - if ctxt.HeadType == objabi.Hwindows { - Segdata.Fileoff = Segrodata.Fileoff + uint64(Rnd(int64(Segrodata.Length), PEFILEALIGN)) - } - if ctxt.HeadType == objabi.Hplan9 { - Segdata.Fileoff = Segtext.Fileoff + Segtext.Filelen - } var data *sym.Section var noptr *sym.Section var bss *sym.Section @@ -2012,16 +2000,14 @@ func (ctxt *Link) address() { } } + // Assign Segdata's Filelen omitting the BSS. We do this here + // simply because right now we know where the BSS starts. Segdata.Filelen = bss.Vaddr - Segdata.Vaddr va = uint64(Rnd(int64(va), int64(*FlagRound))) + order = append(order, &Segdwarf) Segdwarf.Rwx = 06 Segdwarf.Vaddr = va - Segdwarf.Fileoff = Segdata.Fileoff + uint64(Rnd(int64(Segdata.Filelen), int64(*FlagRound))) - Segdwarf.Filelen = 0 - if ctxt.HeadType == objabi.Hwindows { - Segdwarf.Fileoff = Segdata.Fileoff + uint64(Rnd(int64(Segdata.Filelen), PEFILEALIGN)) - } for i, s := range Segdwarf.Sections { vlen := int64(s.Length) if i+1 < len(Segdwarf.Sections) { @@ -2035,8 +2021,6 @@ func (ctxt *Link) address() { Segdwarf.Length = va - Segdwarf.Vaddr } - Segdwarf.Filelen = va - Segdwarf.Vaddr - var ( text = Segtext.Sections[0] rodata = ctxt.Syms.Lookup("runtime.rodata", 0).Sect @@ -2123,6 +2107,41 @@ func (ctxt *Link) address() { ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr)) ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr+noptrbss.Length)) ctxt.xdefine("runtime.end", sym.SBSS, int64(Segdata.Vaddr+Segdata.Length)) + + return order +} + +// layout assigns file offsets and lengths to the segments in order. +func (ctxt *Link) layout(order []*sym.Segment) { + var prev *sym.Segment + for _, seg := range order { + if prev == nil { + seg.Fileoff = uint64(HEADR) + } else { + switch ctxt.HeadType { + default: + // Assuming the previous segment was + // aligned, the following rounding + // should ensure that this segment's + // VA ≡ Fileoff mod FlagRound. + seg.Fileoff = uint64(Rnd(int64(prev.Fileoff+prev.Filelen), int64(*FlagRound))) + if seg.Vaddr%uint64(*FlagRound) != seg.Fileoff%uint64(*FlagRound) { + Exitf("bad segment rounding (Vaddr=%#x Fileoff=%#x FlagRound=%#x)", seg.Vaddr, seg.Fileoff, *FlagRound) + } + case objabi.Hwindows: + seg.Fileoff = prev.Fileoff + uint64(Rnd(int64(prev.Filelen), PEFILEALIGN)) + case objabi.Hplan9: + seg.Fileoff = prev.Fileoff + prev.Filelen + } + } + if seg != &Segdata { + // Link.address already set Segdata.Filelen to + // account for BSS. + seg.Filelen = seg.Length + } + prev = seg + } + } // add a trampoline with symbol s (to be laid down after the current function) diff --git a/src/cmd/link/internal/ld/main.go b/src/cmd/link/internal/ld/main.go index bfa3f70a9ee..23dfa277d0e 100644 --- a/src/cmd/link/internal/ld/main.go +++ b/src/cmd/link/internal/ld/main.go @@ -224,8 +224,9 @@ func Main(arch *sys.Arch, theArch Arch) { ctxt.typelink() ctxt.symtab() ctxt.dodata() - ctxt.address() + order := ctxt.address() ctxt.reloc() + ctxt.layout(order) thearch.Asmb(ctxt) ctxt.undef() ctxt.hostlink()