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cmd/internal/obj/riscv,cmd/link: shorten the riscv64 call sequence 

Now that the other dependent offset has been identified, we can remove the
unnecessary ADDI instruction from the riscv64 call sequence (reducing it
to AUIPC+JALR, rather than the previous AUIPC+ADDI+JALR).

Change-Id: I348c4efb686f9f71ed1dd1d25fb9142a41230b0d
Reviewed-on: https://go-review.googlesource.com/c/go/+/216798
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Joel Sing 2020-01-29 20:14:18 +11:00
parent 2e4f490b31
commit a50c3ffbd4
3 changed files with 4 additions and 14 deletions
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9
src/cmd/internal/obj/riscv/obj.go
View File

@ -55,15 +55,6 @@ func jalrToSym(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc, lr int16) *ob
p.Mark |= NEED_PCREL_ITYPE_RELOC
p = obj.Appendp(p, newprog)
// TODO(jsing): This instruction is not necessary, as the lower bits
// of the immediate can be encoded directly in the JALR instruction.
// However, other code currently depends on jalrToSym being 12 bytes...
p.As = AADDI
p.From = obj.Addr{Type: obj.TYPE_CONST}
p.Reg = REG_TMP
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.From.Type = obj.TYPE_REG

4
src/cmd/link/internal/ld/pcln.go
View File

@ -271,8 +271,8 @@ func (ctxt *Link) pclntab() {
case sys.RISCV64:
// TODO(jsing): The JALR instruction is marked with
// R_CALLRISCV, whereas the actual reloc is currently
// two instructions earlier for the AUIPC+AADI sequence.
deferreturn -= 8
// one instruction earlier starting with the AUIPC.
deferreturn -= 4
case sys.S390X:
deferreturn -= 2
default:

5
src/runtime/asm_riscv64.s
View File

@ -254,12 +254,11 @@ TEXT runtime·gogo(SB), NOSPLIT, $16-8
// func jmpdefer(fv *funcval, argp uintptr)
// called from deferreturn
// 1. grab stored return address from the caller's frame
// 2. sub 12 bytes to get back to JAL deferreturn
// 2. sub 8 bytes to get back to JAL deferreturn
// 3. JMP to fn
// TODO(sorear): There are shorter jump sequences. This function will need to be updated when we use them.
TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
MOV 0(X2), RA
ADD $-12, RA
ADD $-8, RA
MOV fv+0(FP), CTXT
MOV argp+8(FP), X2