CALL and JMP on riscv64 are currently implemented as an AUIPC+JALR pair. This means
that every call requires two instructions and makes use of the REG_TMP register,
even when the symbol would be directly reachable via a single JAL instruction.
Add support for call trampolines - CALL and JMP are now implemented as a single JAL
instruction, with the linker generating trampolines in the case where the symbol is
not reachable (more than +/-1MiB from the JAL instruction), is an unknown symbol or
does not yet have an address assigned. Each trampoline contains an AUIPC+JALR pair,
which the relocation is applied to.
Due to the limited reachability of the JAL instruction, combined with the way that
the Go linker currently assigns symbol addresses, there are cases where a call is to
a symbol that has no address currently assigned. In this situation we have to assume
that a trampoline will be required, however we can patch this up during relocation,
potentially calling directly instead. This means that we will end up with trampolines
that are unused. In the case of the Go binary, there are around 3,500 trampolines of
which approximately 2,300 are unused (around 9200 bytes of machine instructions).
Overall, this removes over 72,000 AUIPC instructions from the Go binary.
Change-Id: I2d9ecfb85dfc285c7729a3cd0b3a77b6f6c98be0
Reviewed-on: https://go-review.googlesource.com/c/go/+/345051
Trust: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
JMP (X5) // 67800200
JMP 4(X5) // 67804200
- // JMP and CALL to symbol are encoded as:
- // AUIPC $0, TMP
- // JALR $0, TMP
- // with a R_RISCV_PCREL_ITYPE relocation - the linker resolves the
- // real address and updates the immediates for both instructions.
- CALL asmtest(SB) // 970f0000
- JMP asmtest(SB) // 970f0000
+ // CALL and JMP to symbol are encoded as JAL (using LR or ZERO
+ // respectively), with a R_RISCV_CALL relocation. The linker resolves
+ // the real address and updates the immediate, using a trampoline in
+ // the case where the address is not directly reachable.
+ CALL asmtest(SB) // ef000000
+ JMP asmtest(SB) // 6f000000
// Branch pseudo-instructions
BEQZ X5, 2(PC) // 63840200
// corresponding *obj.Prog uses the temporary register.
USES_REG_TMP = 1 << iota
+ // NEED_CALL_RELOC is set on JAL instructions to indicate that a
+ // R_RISCV_CALL relocation is needed.
+ NEED_CALL_RELOC
+
// NEED_PCREL_ITYPE_RELOC is set on AUIPC instructions to indicate that
// it is the first instruction in an AUIPC + I-type pair that needs a
// R_RISCV_PCREL_ITYPE relocation.
// Instruction encoding masks.
const (
+ // JTypeImmMask is a mask including only the immediate portion of
+ // J-type instructions.
+ JTypeImmMask = 0xfffff000
+
// ITypeImmMask is a mask including only the immediate portion of
// I-type instructions.
ITypeImmMask = 0xfff00000
// UTypeImmMask is a mask including only the immediate portion of
// U-type instructions.
UTypeImmMask = 0xfffff000
-
- // UJTypeImmMask is a mask including only the immediate portion of
- // UJ-type instructions.
- UJTypeImmMask = UTypeImmMask
)
func buildop(ctxt *obj.Link) {}
-// jalrToSym replaces p with a set of Progs needed to jump to the Sym in p.
-// lr is the link register to use for the JALR.
-// p must be a CALL, JMP or RET.
-func jalrToSym(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc, lr int16) *obj.Prog {
- if p.As != obj.ACALL && p.As != obj.AJMP && p.As != obj.ARET && p.As != obj.ADUFFZERO && p.As != obj.ADUFFCOPY {
- ctxt.Diag("unexpected Prog in jalrToSym: %v", p)
- return p
+func jalToSym(ctxt *obj.Link, p *obj.Prog, lr int16) {
+ switch p.As {
+ case obj.ACALL, obj.AJMP, obj.ARET, obj.ADUFFZERO, obj.ADUFFCOPY:
+ default:
+ ctxt.Diag("unexpected Prog in jalToSym: %v", p)
+ return
}
- // TODO(jsing): Consider using a single JAL instruction and teaching
- // the linker to provide trampolines for the case where the destination
- // offset is too large. This would potentially reduce instructions for
- // the common case, but would require three instructions to go via the
- // trampoline.
-
- to := p.To
-
- p.As = AAUIPC
- p.Mark |= NEED_PCREL_ITYPE_RELOC
- p.SetFrom3(obj.Addr{Type: obj.TYPE_CONST, Offset: to.Offset, Sym: to.Sym})
- p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: 0}
- p.Reg = obj.REG_NONE
- p.To = obj.Addr{Type: obj.TYPE_REG, Reg: REG_TMP}
- p = obj.Appendp(p, newprog)
-
- // Leave Sym only for the CALL reloc in assemble.
- p.As = AJALR
+ p.As = AJAL
+ p.Mark |= NEED_CALL_RELOC
p.From.Type = obj.TYPE_REG
p.From.Reg = lr
p.Reg = obj.REG_NONE
- p.To.Type = obj.TYPE_REG
- p.To.Reg = REG_TMP
- p.To.Sym = to.Sym
-
- return p
}
// progedit is called individually for each *obj.Prog. It normalizes instruction
case obj.ACALL, obj.ADUFFZERO, obj.ADUFFCOPY:
switch p.To.Type {
case obj.TYPE_MEM:
- jalrToSym(ctxt, p, newprog, REG_LR)
+ jalToSym(ctxt, p, REG_LR)
}
case obj.AJMP:
case obj.TYPE_MEM:
switch p.To.Name {
case obj.NAME_EXTERN, obj.NAME_STATIC:
- // JMP to symbol.
- jalrToSym(ctxt, p, newprog, REG_ZERO)
+ jalToSym(ctxt, p, REG_ZERO)
}
}
if retJMP != nil {
p.As = obj.ARET
p.To.Sym = retJMP
- p = jalrToSym(ctxt, p, newprog, REG_ZERO)
+ jalToSym(ctxt, p, REG_ZERO)
} else {
p.As = AJALR
p.From = obj.Addr{Type: obj.TYPE_REG, Reg: REG_ZERO}
rescan = true
}
case AJAL:
+ // Linker will handle the intersymbol case and trampolines.
if p.To.Target() == nil {
- panic("intersymbol jumps should be expressed as AUIPC+JALR")
+ break
}
offset := p.To.Target().Pc - p.Pc
if offset < -(1<<20) || (1<<20) <= offset {
// instructions will break everything--don't do it!
for p := cursym.Func().Text; p != nil; p = p.Link {
switch p.As {
- case ABEQ, ABEQZ, ABGE, ABGEU, ABGEZ, ABGT, ABGTU, ABGTZ, ABLE, ABLEU, ABLEZ, ABLT, ABLTU, ABLTZ, ABNE, ABNEZ, AJAL:
+ case ABEQ, ABEQZ, ABGE, ABGEU, ABGEZ, ABGT, ABGTU, ABGTZ, ABLE, ABLEU, ABLEZ, ABLT, ABLTU, ABLTZ, ABNE, ABNEZ:
switch p.To.Type {
case obj.TYPE_BRANCH:
p.To.Type, p.To.Offset = obj.TYPE_CONST, p.To.Target().Pc-p.Pc
panic("unhandled type")
}
+ case AJAL:
+ // Linker will handle the intersymbol case and trampolines.
+ if p.To.Target() != nil {
+ p.To.Type, p.To.Offset = obj.TYPE_CONST, p.To.Target().Pc-p.Pc
+ }
+
case AAUIPC:
if p.From.Type == obj.TYPE_BRANCH {
low, high, err := Split32BitImmediate(p.From.Target().Pc - p.Pc)
if to_more != nil {
to_more.To.SetTarget(p)
}
- p = jalrToSym(ctxt, p, newprog, REG_X5)
+ jalToSym(ctxt, p, REG_X5)
// JMP start
p = obj.Appendp(p, newprog)
return imm<<12 | rd<<7 | enc.opcode
}
+// encodeJImmediate encodes an immediate for a J-type RISC-V instruction.
+func encodeJImmediate(imm uint32) uint32 {
+ return (imm>>20)<<31 | ((imm>>1)&0x3ff)<<21 | ((imm>>11)&0x1)<<20 | ((imm>>12)&0xff)<<12
+}
+
// encodeJ encodes a J-type RISC-V instruction.
func encodeJ(ins *instruction) uint32 {
imm := immI(ins.as, ins.imm, 21)
if enc == nil {
panic("encodeJ: could not encode instruction")
}
- return (imm>>20)<<31 | ((imm>>1)&0x3ff)<<21 | ((imm>>11)&0x1)<<20 | ((imm>>12)&0xff)<<12 | rd<<7 | enc.opcode
+ return encodeJImmediate(imm) | rd<<7 | enc.opcode
}
func encodeRawIns(ins *instruction) uint32 {
return uint32(ins.imm)
}
+func EncodeJImmediate(imm int64) (int64, error) {
+ if !immIFits(imm, 21) {
+ return 0, fmt.Errorf("immediate %#x does not fit in 21 bits", imm)
+ }
+ if imm&1 != 0 {
+ return 0, fmt.Errorf("immediate %#x is not a multiple of two", imm)
+ }
+ return int64(encodeJImmediate(uint32(imm))), nil
+}
+
func EncodeIImmediate(imm int64) (int64, error) {
if !immIFits(imm, 12) {
return 0, fmt.Errorf("immediate %#x does not fit in 12 bits", imm)
for p := cursym.Func().Text; p != nil; p = p.Link {
switch p.As {
- case AJALR:
- if p.To.Sym != nil {
- // This is a CALL/JMP. We add a relocation only
- // for linker stack checking. No actual
- // relocation is needed.
+ case AJAL:
+ if p.Mark&NEED_CALL_RELOC == NEED_CALL_RELOC {
rel := obj.Addrel(cursym)
rel.Off = int32(p.Pc)
rel.Siz = 4
rel.Sym = p.To.Sym
rel.Add = p.To.Offset
- rel.Type = objabi.R_CALLRISCV
+ rel.Type = objabi.R_RISCV_CALL
+ }
+ case AJALR:
+ if p.To.Sym != nil {
+ ctxt.Diag("%v: unexpected AJALR with to symbol", p)
}
case AAUIPC, AMOV, AMOVB, AMOVH, AMOVW, AMOVBU, AMOVHU, AMOVWU, AMOVF, AMOVD:
// R_CALLMIPS (only used on mips64) resolves to non-PC-relative target address
// of a CALL (JAL) instruction, by encoding the address into the instruction.
R_CALLMIPS
- // R_CALLRISCV marks RISC-V CALLs for stack checking.
- R_CALLRISCV
R_CONST
R_PCREL
// R_TLS_LE, used on 386, amd64, and ARM, resolves to the offset of the
// RISC-V.
+ // R_RISCV_CALL relocates a J-type instruction with a 21 bit PC-relative
+ // address.
+ R_RISCV_CALL
+
+ // R_RISCV_CALL_TRAMP is the same as R_RISCV_CALL but denotes the use of a
+ // trampoline, which we may be able to avoid during relocation. These are
+ // only used by the linker and are not emitted by the compiler or assembler.
+ R_RISCV_CALL_TRAMP
+
// R_RISCV_PCREL_ITYPE resolves a 32-bit PC-relative address using an
// AUIPC + I-type instruction pair.
R_RISCV_PCREL_ITYPE
// the target address in register or memory.
func (r RelocType) IsDirectCall() bool {
switch r {
- case R_CALL, R_CALLARM, R_CALLARM64, R_CALLMIPS, R_CALLPOWER, R_CALLRISCV:
+ case R_CALL, R_CALLARM, R_CALLARM64, R_CALLMIPS, R_CALLPOWER, R_RISCV_CALL, R_RISCV_CALL_TRAMP:
return true
}
return false
_ = x[R_CALLIND-10]
_ = x[R_CALLPOWER-11]
_ = x[R_CALLMIPS-12]
- _ = x[R_CALLRISCV-13]
- _ = x[R_CONST-14]
- _ = x[R_PCREL-15]
- _ = x[R_TLS_LE-16]
- _ = x[R_TLS_IE-17]
- _ = x[R_GOTOFF-18]
- _ = x[R_PLT0-19]
- _ = x[R_PLT1-20]
- _ = x[R_PLT2-21]
- _ = x[R_USEFIELD-22]
- _ = x[R_USETYPE-23]
- _ = x[R_USEIFACE-24]
- _ = x[R_USEIFACEMETHOD-25]
- _ = x[R_METHODOFF-26]
- _ = x[R_KEEP-27]
- _ = x[R_POWER_TOC-28]
- _ = x[R_GOTPCREL-29]
- _ = x[R_JMPMIPS-30]
- _ = x[R_DWARFSECREF-31]
- _ = x[R_DWARFFILEREF-32]
- _ = x[R_ARM64_TLS_LE-33]
- _ = x[R_ARM64_TLS_IE-34]
- _ = x[R_ARM64_GOTPCREL-35]
- _ = x[R_ARM64_GOT-36]
- _ = x[R_ARM64_PCREL-37]
- _ = x[R_ARM64_LDST8-38]
- _ = x[R_ARM64_LDST16-39]
- _ = x[R_ARM64_LDST32-40]
- _ = x[R_ARM64_LDST64-41]
- _ = x[R_ARM64_LDST128-42]
- _ = x[R_POWER_TLS_LE-43]
- _ = x[R_POWER_TLS_IE-44]
- _ = x[R_POWER_TLS-45]
- _ = x[R_ADDRPOWER_DS-46]
- _ = x[R_ADDRPOWER_GOT-47]
- _ = x[R_ADDRPOWER_PCREL-48]
- _ = x[R_ADDRPOWER_TOCREL-49]
- _ = x[R_ADDRPOWER_TOCREL_DS-50]
- _ = x[R_RISCV_PCREL_ITYPE-51]
- _ = x[R_RISCV_PCREL_STYPE-52]
- _ = x[R_RISCV_TLS_IE_ITYPE-53]
- _ = x[R_RISCV_TLS_IE_STYPE-54]
- _ = x[R_PCRELDBL-55]
- _ = x[R_ADDRMIPSU-56]
- _ = x[R_ADDRMIPSTLS-57]
- _ = x[R_ADDRCUOFF-58]
- _ = x[R_WASMIMPORT-59]
- _ = x[R_XCOFFREF-60]
+ _ = x[R_CONST-13]
+ _ = x[R_PCREL-14]
+ _ = x[R_TLS_LE-15]
+ _ = x[R_TLS_IE-16]
+ _ = x[R_GOTOFF-17]
+ _ = x[R_PLT0-18]
+ _ = x[R_PLT1-19]
+ _ = x[R_PLT2-20]
+ _ = x[R_USEFIELD-21]
+ _ = x[R_USETYPE-22]
+ _ = x[R_USEIFACE-23]
+ _ = x[R_USEIFACEMETHOD-24]
+ _ = x[R_METHODOFF-25]
+ _ = x[R_KEEP-26]
+ _ = x[R_POWER_TOC-27]
+ _ = x[R_GOTPCREL-28]
+ _ = x[R_JMPMIPS-29]
+ _ = x[R_DWARFSECREF-30]
+ _ = x[R_DWARFFILEREF-31]
+ _ = x[R_ARM64_TLS_LE-32]
+ _ = x[R_ARM64_TLS_IE-33]
+ _ = x[R_ARM64_GOTPCREL-34]
+ _ = x[R_ARM64_GOT-35]
+ _ = x[R_ARM64_PCREL-36]
+ _ = x[R_ARM64_LDST8-37]
+ _ = x[R_ARM64_LDST16-38]
+ _ = x[R_ARM64_LDST32-39]
+ _ = x[R_ARM64_LDST64-40]
+ _ = x[R_ARM64_LDST128-41]
+ _ = x[R_POWER_TLS_LE-42]
+ _ = x[R_POWER_TLS_IE-43]
+ _ = x[R_POWER_TLS-44]
+ _ = x[R_ADDRPOWER_DS-45]
+ _ = x[R_ADDRPOWER_GOT-46]
+ _ = x[R_ADDRPOWER_PCREL-47]
+ _ = x[R_ADDRPOWER_TOCREL-48]
+ _ = x[R_ADDRPOWER_TOCREL_DS-49]
+ _ = x[R_RISCV_CALL-50]
+ _ = x[R_RISCV_CALL_TRAMP-51]
+ _ = x[R_RISCV_PCREL_ITYPE-52]
+ _ = x[R_RISCV_PCREL_STYPE-53]
+ _ = x[R_RISCV_TLS_IE_ITYPE-54]
+ _ = x[R_RISCV_TLS_IE_STYPE-55]
+ _ = x[R_PCRELDBL-56]
+ _ = x[R_ADDRMIPSU-57]
+ _ = x[R_ADDRMIPSTLS-58]
+ _ = x[R_ADDRCUOFF-59]
+ _ = x[R_WASMIMPORT-60]
+ _ = x[R_XCOFFREF-61]
}
-const _RelocType_name = "R_ADDRR_ADDRPOWERR_ADDRARM64R_ADDRMIPSR_ADDROFFR_SIZER_CALLR_CALLARMR_CALLARM64R_CALLINDR_CALLPOWERR_CALLMIPSR_CALLRISCVR_CONSTR_PCRELR_TLS_LER_TLS_IER_GOTOFFR_PLT0R_PLT1R_PLT2R_USEFIELDR_USETYPER_USEIFACER_USEIFACEMETHODR_METHODOFFR_KEEPR_POWER_TOCR_GOTPCRELR_JMPMIPSR_DWARFSECREFR_DWARFFILEREFR_ARM64_TLS_LER_ARM64_TLS_IER_ARM64_GOTPCRELR_ARM64_GOTR_ARM64_PCRELR_ARM64_LDST8R_ARM64_LDST16R_ARM64_LDST32R_ARM64_LDST64R_ARM64_LDST128R_POWER_TLS_LER_POWER_TLS_IER_POWER_TLSR_ADDRPOWER_DSR_ADDRPOWER_GOTR_ADDRPOWER_PCRELR_ADDRPOWER_TOCRELR_ADDRPOWER_TOCREL_DSR_RISCV_PCREL_ITYPER_RISCV_PCREL_STYPER_RISCV_TLS_IE_ITYPER_RISCV_TLS_IE_STYPER_PCRELDBLR_ADDRMIPSUR_ADDRMIPSTLSR_ADDRCUOFFR_WASMIMPORTR_XCOFFREF"
+const _RelocType_name = "R_ADDRR_ADDRPOWERR_ADDRARM64R_ADDRMIPSR_ADDROFFR_SIZER_CALLR_CALLARMR_CALLARM64R_CALLINDR_CALLPOWERR_CALLMIPSR_CONSTR_PCRELR_TLS_LER_TLS_IER_GOTOFFR_PLT0R_PLT1R_PLT2R_USEFIELDR_USETYPER_USEIFACER_USEIFACEMETHODR_METHODOFFR_KEEPR_POWER_TOCR_GOTPCRELR_JMPMIPSR_DWARFSECREFR_DWARFFILEREFR_ARM64_TLS_LER_ARM64_TLS_IER_ARM64_GOTPCRELR_ARM64_GOTR_ARM64_PCRELR_ARM64_LDST8R_ARM64_LDST16R_ARM64_LDST32R_ARM64_LDST64R_ARM64_LDST128R_POWER_TLS_LER_POWER_TLS_IER_POWER_TLSR_ADDRPOWER_DSR_ADDRPOWER_GOTR_ADDRPOWER_PCRELR_ADDRPOWER_TOCRELR_ADDRPOWER_TOCREL_DSR_RISCV_CALLR_RISCV_CALL_TRAMPR_RISCV_PCREL_ITYPER_RISCV_PCREL_STYPER_RISCV_TLS_IE_ITYPER_RISCV_TLS_IE_STYPER_PCRELDBLR_ADDRMIPSUR_ADDRMIPSTLSR_ADDRCUOFFR_WASMIMPORTR_XCOFFREF"
-var _RelocType_index = [...]uint16{0, 6, 17, 28, 38, 47, 53, 59, 68, 79, 88, 99, 109, 120, 127, 134, 142, 150, 158, 164, 170, 176, 186, 195, 205, 221, 232, 238, 249, 259, 268, 281, 295, 309, 323, 339, 350, 363, 376, 390, 404, 418, 433, 447, 461, 472, 486, 501, 518, 536, 557, 576, 595, 615, 635, 645, 656, 669, 680, 692, 702}
+var _RelocType_index = [...]uint16{0, 6, 17, 28, 38, 47, 53, 59, 68, 79, 88, 99, 109, 116, 123, 131, 139, 147, 153, 159, 165, 175, 184, 194, 210, 221, 227, 238, 248, 257, 270, 284, 298, 312, 328, 339, 352, 365, 379, 393, 407, 422, 436, 450, 461, 475, 490, 507, 525, 546, 558, 576, 595, 614, 634, 654, 664, 675, 688, 699, 711, 721}
func (i RelocType) String() string {
i -= 1
panic("unreachable")
}
-// detect too-far jumps in function s, and add trampolines if necessary
-// ARM, PPC64 & PPC64LE support trampoline insertion for internal and external linking
-// On PPC64 & PPC64LE the text sections might be split but will still insert trampolines
-// where necessary.
+// Detect too-far jumps in function s, and add trampolines if necessary.
+// ARM, PPC64, PPC64LE and RISCV64 support trampoline insertion for internal
+// and external linking. On PPC64 and PPC64LE the text sections might be split
+// but will still insert trampolines where necessary.
func trampoline(ctxt *Link, s loader.Sym) {
if thearch.Trampoline == nil {
return // no need or no support of trampolines on this arch
if !ldr.AttrReachable(rs) || ldr.SymType(rs) == sym.Sxxx {
continue // something is wrong. skip it here and we'll emit a better error later
}
- if ldr.SymValue(rs) == 0 && (ldr.SymType(rs) != sym.SDYNIMPORT && ldr.SymType(rs) != sym.SUNDEFEXT) {
+
+ // RISC-V is only able to reach +/-1MiB via a JAL instruction,
+ // which we can readily exceed in the same package. As such, we
+ // need to generate trampolines when the address is unknown.
+ if ldr.SymValue(rs) == 0 && !ctxt.Target.IsRISCV64() && ldr.SymType(rs) != sym.SDYNIMPORT && ldr.SymType(rs) != sym.SUNDEFEXT {
if ldr.SymPkg(s) != "" && ldr.SymPkg(rs) == ldr.SymPkg(s) {
// Symbols in the same package are laid out together.
// Except that if SymPkg(s) == "", it is a host object symbol
continue // runtime packages are laid out together
}
}
-
thearch.Trampoline(ctxt, ldr, ri, rs, s)
}
}
switch target.Arch.Family {
case sys.AMD64, sys.I386:
deferreturn--
- case sys.PPC64, sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64:
+ case sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64, sys.PPC64, sys.RISCV64:
// no change
- case sys.RISCV64:
- // TODO(jsing): The JALR instruction is marked with
- // R_CALLRISCV, whereas the actual reloc is currently
- // one instruction earlier starting with the AUIPC.
- deferreturn -= 4
case sys.S390X:
deferreturn -= 2
default:
}
out.Write64(uint64(r.Xadd))
- case objabi.R_CALLRISCV:
- // Call relocations are currently handled via R_RISCV_PCREL_ITYPE.
- // TODO(jsing): Consider generating elf.R_RISCV_CALL instead of a
- // HI20/LO12_I pair.
+ case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
+ out.Write64(uint64(sectoff))
+ out.Write64(uint64(elf.R_RISCV_JAL) | uint64(elfsym)<<32)
+ out.Write64(uint64(r.Xadd))
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
// Find the text symbol for the AUIPC instruction targeted
}
func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loader.Reloc, s loader.Sym, val int64) (o int64, nExtReloc int, ok bool) {
+ rs := r.Sym()
+ pc := ldr.SymValue(s) + int64(r.Off())
+
+ // If the call points to a trampoline, see if we can reach the symbol
+ // directly. This situation can occur when the relocation symbol is
+ // not assigned an address until after the trampolines are generated.
+ if r.Type() == objabi.R_RISCV_CALL_TRAMP {
+ relocs := ldr.Relocs(rs)
+ if relocs.Count() != 1 {
+ ldr.Errorf(s, "trampoline %v has %d relocations", ldr.SymName(rs), relocs.Count())
+ }
+ tr := relocs.At(0)
+ if tr.Type() != objabi.R_RISCV_PCREL_ITYPE {
+ ldr.Errorf(s, "trampoline %v has unexpected relocation %v", ldr.SymName(rs), tr.Type())
+ }
+ trs := tr.Sym()
+ if ldr.SymValue(trs) != 0 && ldr.SymType(trs) != sym.SDYNIMPORT && ldr.SymType(trs) != sym.SUNDEFEXT {
+ trsOff := ldr.SymValue(trs) + tr.Add() - pc
+ if trsOff >= -(1<<20) && trsOff < (1<<20) {
+ r.SetType(objabi.R_RISCV_CALL)
+ r.SetSym(trs)
+ r.SetAdd(tr.Add())
+ rs = trs
+ }
+ }
+
+ }
+
if target.IsExternal() {
switch r.Type() {
- case objabi.R_CALLRISCV:
- return val, 0, true
+ case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
+ return val, 1, true
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
return val, 2, true
return val, 0, false
}
- rs := r.Sym()
+ off := ldr.SymValue(rs) + r.Add() - pc
switch r.Type() {
- case objabi.R_CALLRISCV:
- // Nothing to do.
+ case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
+ // Generate instruction immediates.
+ imm, err := riscv.EncodeJImmediate(off)
+ if err != nil {
+ ldr.Errorf(s, "cannot encode R_RISCV_CALL relocation offset for %s: %v", ldr.SymName(rs), err)
+ }
+ immMask := int64(riscv.JTypeImmMask)
+
+ val = (val &^ immMask) | int64(imm)
+
return val, 0, true
case objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
return ebreakIns<<32 | ebreakIns, 0, true
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE:
- pc := ldr.SymValue(s) + int64(r.Off())
- off := ldr.SymValue(rs) + r.Add() - pc
-
// Generate AUIPC and second instruction immediates.
low, high, err := riscv.Split32BitImmediate(off)
if err != nil {
func extreloc(target *ld.Target, ldr *loader.Loader, r loader.Reloc, s loader.Sym) (loader.ExtReloc, bool) {
switch r.Type() {
+ case objabi.R_RISCV_CALL, objabi.R_RISCV_CALL_TRAMP:
+ return ld.ExtrelocSimple(ldr, r), true
+
case objabi.R_RISCV_PCREL_ITYPE, objabi.R_RISCV_PCREL_STYPE, objabi.R_RISCV_TLS_IE_ITYPE, objabi.R_RISCV_TLS_IE_STYPE:
return ld.ExtrelocViaOuterSym(ldr, r, s), true
}
return loader.ExtReloc{}, false
}
+
+func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
+ relocs := ldr.Relocs(s)
+ r := relocs.At(ri)
+
+ switch r.Type() {
+ case objabi.R_RISCV_CALL:
+ pc := ldr.SymValue(s) + int64(r.Off())
+ off := ldr.SymValue(rs) + r.Add() - pc
+
+ // Relocation symbol has an address and is directly reachable,
+ // therefore there is no need for a trampoline.
+ if ldr.SymValue(rs) != 0 && off >= -(1<<20) && off < (1<<20) && (*ld.FlagDebugTramp <= 1 || ldr.SymPkg(s) == ldr.SymPkg(rs)) {
+ break
+ }
+
+ // Relocation symbol is too far for a direct call or has not
+ // yet been given an address. See if an existing trampoline is
+ // reachable and if so, reuse it. Otherwise we need to create
+ // a new trampoline.
+ var tramp loader.Sym
+ for i := 0; ; i++ {
+ oName := ldr.SymName(rs)
+ name := fmt.Sprintf("%s-tramp%d", oName, i)
+ if r.Add() != 0 {
+ name = fmt.Sprintf("%s%+x-tramp%d", oName, r.Add(), i)
+ }
+ tramp = ldr.LookupOrCreateSym(name, int(ldr.SymVersion(rs)))
+ ldr.SetAttrReachable(tramp, true)
+ if ldr.SymType(tramp) == sym.SDYNIMPORT {
+ // Do not reuse trampoline defined in other module.
+ continue
+ }
+ if oName == "runtime.deferreturn" {
+ ldr.SetIsDeferReturnTramp(tramp, true)
+ }
+ if ldr.SymValue(tramp) == 0 {
+ // Either trampoline does not exist or we found one
+ // that does not have an address assigned and will be
+ // laid down immediately after the current function.
+ break
+ }
+
+ trampOff := ldr.SymValue(tramp) - (ldr.SymValue(s) + int64(r.Off()))
+ if trampOff >= -(1<<20) && trampOff < (1<<20) {
+ // An existing trampoline that is reachable.
+ break
+ }
+ }
+ if ldr.SymType(tramp) == 0 {
+ trampb := ldr.MakeSymbolUpdater(tramp)
+ ctxt.AddTramp(trampb)
+ genCallTramp(ctxt.Arch, ctxt.LinkMode, ldr, trampb, rs, int64(r.Add()))
+ }
+ sb := ldr.MakeSymbolUpdater(s)
+ if ldr.SymValue(rs) == 0 {
+ // In this case the target symbol has not yet been assigned an
+ // address, so we have to assume a trampoline is required. Mark
+ // this as a call via a trampoline so that we can potentially
+ // switch to a direct call during relocation.
+ sb.SetRelocType(ri, objabi.R_RISCV_CALL_TRAMP)
+ }
+ relocs := sb.Relocs()
+ r := relocs.At(ri)
+ r.SetSym(tramp)
+ r.SetAdd(0)
+
+ default:
+ ctxt.Errorf(s, "trampoline called with non-jump reloc: %d (%s)", r.Type(), sym.RelocName(ctxt.Arch, r.Type()))
+ }
+}
+
+func genCallTramp(arch *sys.Arch, linkmode ld.LinkMode, ldr *loader.Loader, tramp *loader.SymbolBuilder, target loader.Sym, offset int64) {
+ tramp.AddUint32(arch, 0x00000f97) // AUIPC $0, X31
+ tramp.AddUint32(arch, 0x000f8067) // JALR X0, (X31)
+
+ r, _ := tramp.AddRel(objabi.R_RISCV_PCREL_ITYPE)
+ r.SetSiz(8)
+ r.SetSym(target)
+ r.SetAdd(offset)
+}
Elfreloc1: elfreloc1,
ElfrelocSize: 24,
Elfsetupplt: elfsetupplt,
- Gentext: gentext,
- GenSymsLate: genSymsLate,
- Machoreloc1: machoreloc1,
+
+ // TrampLimit is set such that we always run the trampoline
+ // generation code. This is necessary since calls to external
+ // symbols require the use of trampolines, regardless of the
+ // text size.
+ TrampLimit: 1,
+ Trampoline: trampoline,
+
+ Gentext: gentext,
+ GenSymsLate: genSymsLate,
+ Machoreloc1: machoreloc1,
Linuxdynld: "/lib/ld.so.1",