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cmd/link,debug/elf: mips32, add .gnu.attributes and .MIPS.abiflags sections

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MIPS32 uses .gnu.attributes and .MIPS.abiflags sections to mark FP ABI
the object is using, and the kernel will set the correct FP mode for it.

Currrently Go doesn't generate these 2 sections. If we link object
without these 2 sections togather FPXX objects, the result will be FPXX,
which is wrong:
   FP32 + FPXX -> FP32
   FPXX + FP64 -> FP64
   FP32 + FP64 -> reject

These 2 sections is also needed to support FPXX and FP64 in future.

More details about FP32/FPXX/FP64 are explained in:
    https://web.archive.org/web/20180828210612/https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking

Fixes #39677

Change-Id: Ia34e7461dee38a4f575dd8ace609988744512ac1
Reviewed-on: https://go-review.googlesource.com/c/go/+/239217
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Meng Zhuo <mzh@golangcn.org>
This commit is contained in:
YunQiang Su 2020-06-20 14:04:54 +00:00 committed by Cherry Zhang
parent 700b73975e
commit ff5cf4ced3
2 changed files with 147 additions and 0 deletions
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145
src/cmd/link/internal/ld/elf.go
View File

@ -519,6 +519,90 @@ func elfwriteinterp(out *OutBuf) int {
return int(sh.Size)
}
// member of .gnu.attributes of MIPS for fpAbi
const (
// No floating point is present in the module (default)
MIPS_FPABI_NONE = 0
// FP code in the module uses the FP32 ABI for a 32-bit ABI
MIPS_FPABI_ANY = 1
// FP code in the module only uses single precision ABI
MIPS_FPABI_SINGLE = 2
// FP code in the module uses soft-float ABI
MIPS_FPABI_SOFT = 3
// FP code in the module assumes an FPU with FR=1 and has 12
// callee-saved doubles. Historic, no longer supported.
MIPS_FPABI_HIST = 4
// FP code in the module uses the FPXX ABI
MIPS_FPABI_FPXX = 5
// FP code in the module uses the FP64 ABI
MIPS_FPABI_FP64 = 6
// FP code in the module uses the FP64A ABI
MIPS_FPABI_FP64A = 7
)
func elfMipsAbiFlags(sh *ElfShdr, startva uint64, resoff uint64) int {
n := 24
sh.Addr = startva + resoff - uint64(n)
sh.Off = resoff - uint64(n)
sh.Size = uint64(n)
sh.Type = uint32(elf.SHT_MIPS_ABIFLAGS)
sh.Flags = uint64(elf.SHF_ALLOC)
return n
}
//typedef struct
//{
// /* Version of flags structure. */
// uint16_t version;
// /* The level of the ISA: 1-5, 32, 64. */
// uint8_t isa_level;
// /* The revision of ISA: 0 for MIPS V and below, 1-n otherwise. */
// uint8_t isa_rev;
// /* The size of general purpose registers. */
// uint8_t gpr_size;
// /* The size of co-processor 1 registers. */
// uint8_t cpr1_size;
// /* The size of co-processor 2 registers. */
// uint8_t cpr2_size;
// /* The floating-point ABI. */
// uint8_t fp_abi;
// /* Processor-specific extension. */
// uint32_t isa_ext;
// /* Mask of ASEs used. */
// uint32_t ases;
// /* Mask of general flags. */
// uint32_t flags1;
// uint32_t flags2;
//} Elf_Internal_ABIFlags_v0;
func elfWriteMipsAbiFlags(ctxt *Link) int {
sh := elfshname(".MIPS.abiflags")
ctxt.Out.SeekSet(int64(sh.Off))
ctxt.Out.Write16(0) // version
ctxt.Out.Write8(32) // isaLevel
ctxt.Out.Write8(1) // isaRev
ctxt.Out.Write8(1) // gprSize
ctxt.Out.Write8(1) // cpr1Size
ctxt.Out.Write8(0) // cpr2Size
if objabi.GOMIPS == "softfloat" {
ctxt.Out.Write8(MIPS_FPABI_SOFT) // fpAbi
} else {
// Go cannot make sure non odd-number-fpr is used (ie, in load a double from memory).
// So, we mark the object is MIPS I style paired float/double register scheme,
// aka MIPS_FPABI_ANY. If we mark the object as FPXX, the kernel may use FR=1 mode,
// then we meet some problem.
// Note: MIPS_FPABI_ANY is bad naming: in fact it is MIPS I style FPR usage.
// It is not for 'ANY'.
// TODO: switch to FPXX after be sure that no odd-number-fpr is used.
ctxt.Out.Write8(MIPS_FPABI_ANY) // fpAbi
}
ctxt.Out.Write32(0) // isaExt
ctxt.Out.Write32(0) // ases
ctxt.Out.Write32(0) // flags1
ctxt.Out.Write32(0) // flags2
return int(sh.Size)
}
func elfnote(sh *ElfShdr, startva uint64, resoff uint64, sz int) int {
n := 3*4 + uint64(sz) + resoff%4
@ -1204,6 +1288,10 @@ func (ctxt *Link) doelf() {
shstrtab.Addstring(".noptrbss")
shstrtab.Addstring("__libfuzzer_extra_counters")
shstrtab.Addstring(".go.buildinfo")
if ctxt.IsMIPS() {
shstrtab.Addstring(".MIPS.abiflags")
shstrtab.Addstring(".gnu.attributes")
}
// generate .tbss section for dynamic internal linker or external
// linking, so that various binutils could correctly calculate
@ -1254,6 +1342,10 @@ func (ctxt *Link) doelf() {
shstrtab.Addstring(elfRelType + ".data.rel.ro")
}
shstrtab.Addstring(elfRelType + ".go.buildinfo")
if ctxt.IsMIPS() {
shstrtab.Addstring(elfRelType + ".MIPS.abiflags")
shstrtab.Addstring(elfRelType + ".gnu.attributes")
}
// add a .note.GNU-stack section to mark the stack as non-executable
shstrtab.Addstring(".note.GNU-stack")
@ -1445,6 +1537,36 @@ func (ctxt *Link) doelf() {
if ctxt.LinkMode == LinkExternal && *flagBuildid != "" {
addgonote(ctxt, ".note.go.buildid", ELF_NOTE_GOBUILDID_TAG, []byte(*flagBuildid))
}
//type mipsGnuAttributes struct {
// version uint8 // 'A'
// length uint32 // 15 including itself
// gnu [4]byte // "gnu\0"
// tag uint8 // 1:file, 2: section, 3: symbol, 1 here
// taglen uint32 // tag length, including tag, 7 here
// tagfp uint8 // 4
// fpAbi uint8 // see .MIPS.abiflags
//}
if ctxt.IsMIPS() {
gnuattributes := ldr.CreateSymForUpdate(".gnu.attributes", 0)
gnuattributes.SetType(sym.SELFROSECT)
gnuattributes.SetReachable(true)
gnuattributes.AddUint8('A') // version 'A'
gnuattributes.AddUint32(ctxt.Arch, 15) // length 15 including itself
gnuattributes.AddBytes([]byte("gnu\x00")) // "gnu\0"
gnuattributes.AddUint8(1) // 1:file, 2: section, 3: symbol, 1 here
gnuattributes.AddUint32(ctxt.Arch, 7) // tag length, including tag, 7 here
gnuattributes.AddUint8(4) // 4 for FP, 8 for MSA
if objabi.GOMIPS == "softfloat" {
gnuattributes.AddUint8(MIPS_FPABI_SOFT)
} else {
// Note: MIPS_FPABI_ANY is bad naming: in fact it is MIPS I style FPR usage.
// It is not for 'ANY'.
// TODO: switch to FPXX after be sure that no odd-number-fpr is used.
gnuattributes.AddUint8(MIPS_FPABI_ANY)
}
}
}
// Do not write DT_NULL. elfdynhash will finish it.
@ -1910,6 +2032,25 @@ elfobj:
shsym(sh, ldr, ldr.Lookup(".shstrtab", 0))
eh.Shstrndx = uint16(sh.shnum)
if ctxt.IsMIPS() {
sh = elfshname(".MIPS.abiflags")
sh.Type = uint32(elf.SHT_MIPS_ABIFLAGS)
sh.Flags = uint64(elf.SHF_ALLOC)
sh.Addralign = 8
resoff -= int64(elfMipsAbiFlags(sh, uint64(startva), uint64(resoff)))
ph := newElfPhdr()
ph.Type = elf.PT_MIPS_ABIFLAGS
ph.Flags = elf.PF_R
phsh(ph, sh)
sh = elfshname(".gnu.attributes")
sh.Type = uint32(elf.SHT_GNU_ATTRIBUTES)
sh.Addralign = 1
ldr := ctxt.loader
shsym(sh, ldr, ldr.Lookup(".gnu.attributes", 0))
}
// put these sections early in the list
if !*FlagS {
elfshname(".symtab")
@ -2029,6 +2170,10 @@ elfobj:
if !*FlagD {
a += int64(elfwriteinterp(ctxt.Out))
}
if ctxt.IsMIPS() {
a += int64(elfWriteMipsAbiFlags(ctxt))
}
if ctxt.LinkMode != LinkExternal {
if ctxt.HeadType == objabi.Hnetbsd {
a += int64(elfwritenetbsdsig(ctxt.Out))

2
src/debug/elf/elf.go
View File

@ -644,6 +644,7 @@ const (
SHT_GNU_VERSYM SectionType = 0x6fffffff /* GNU version symbol table */
SHT_HIOS SectionType = 0x6fffffff /* Last of OS specific semantics */
SHT_LOPROC SectionType = 0x70000000 /* reserved range for processor */
SHT_MIPS_ABIFLAGS SectionType = 0x7000002a /* .MIPS.abiflags */
SHT_HIPROC SectionType = 0x7fffffff /* specific section header types */
SHT_LOUSER SectionType = 0x80000000 /* reserved range for application */
SHT_HIUSER SectionType = 0xffffffff /* specific indexes */
@ -675,6 +676,7 @@ var shtStrings = []intName{
{0x6ffffffe, "SHT_GNU_VERNEED"},
{0x6fffffff, "SHT_GNU_VERSYM"},
{0x70000000, "SHT_LOPROC"},
{0x7000002a, "SHT_MIPS_ABIFLAGS"},
{0x7fffffff, "SHT_HIPROC"},
{0x80000000, "SHT_LOUSER"},
{0xffffffff, "SHT_HIUSER"},