cmd/internal/obj/arm64: improve comment and signature of pcAlignPadLength

The function just calculates the number of needed padding bytes,
instead of actually carrying out the alignment operation. And it has
the context argument at the end of the argument list, while contexts
idiomatically come first. Indeed, this is the only case in
cmd/internal/obj where ctxt is not the only argument and does not come
first.

Fix those two nits; no functional change intended.

Suggested by Ian during review of CL 479815 (that introduces a copy of
this helper into the loong64 port).

Change-Id: Ieb221ead23282abe6e04804d537e1234c7ab21d0
Reviewed-on: https://go-review.googlesource.com/c/go/+/483155
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

diff --git a/src/cmd/internal/obj/arm64/asm7.go b/src/cmd/internal/obj/arm64/asm7.go
index 0abb90b1e08be4315d96674693236fdd0e81ed24..4906839cf777f14e994c853c8de0c2e4f1455c68 100644 (file)
--- a/src/cmd/internal/obj/arm64/asm7.go
+++ b/src/cmd/internal/obj/arm64/asm7.go
@@ -1015,8 +1015,9 @@ var sysInstFields = map[SpecialOperand]struct {
 // Used for padding NOOP instruction
 const OP_NOOP = 0xd503201f
 
-// align code to a certain length by padding bytes.
-func pcAlignPadLength(pc int64, alignedValue int64, ctxt *obj.Link) int {
+// pcAlignPadLength returns the number of bytes required to align pc to alignedValue,
+// reporting an error if alignedValue is not a power of two or is out of range.
+func pcAlignPadLength(ctxt *obj.Link, pc int64, alignedValue int64) int {
        if !((alignedValue&(alignedValue-1) == 0) && 8 <= alignedValue && alignedValue <= 2048) {
                ctxt.Diag("alignment value of an instruction must be a power of two and in the range [8, 2048], got %d\n", alignedValue)
        }
@@ -1075,7 +1076,7 @@ func span7(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
                        switch p.As {
                        case obj.APCALIGN:
                                alignedValue := p.From.Offset
-                               m = pcAlignPadLength(pc, alignedValue, ctxt)
+                               m = pcAlignPadLength(ctxt, pc, alignedValue)
                                // Update the current text symbol alignment value.
                                if int32(alignedValue) > cursym.Func().Align {
                                        cursym.Func().Align = int32(alignedValue)
@@ -1150,7 +1151,7 @@ func span7(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
                                switch p.As {
                                case obj.APCALIGN:
                                        alignedValue := p.From.Offset
-                                       m = pcAlignPadLength(pc, alignedValue, ctxt)
+                                       m = pcAlignPadLength(ctxt, pc, alignedValue)
                                        break
                                case obj.ANOP, obj.AFUNCDATA, obj.APCDATA:
                                        continue
@@ -1183,7 +1184,7 @@ func span7(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
                }
                if p.As == obj.APCALIGN {
                        alignedValue := p.From.Offset
-                       v := pcAlignPadLength(p.Pc, alignedValue, c.ctxt)
+                       v := pcAlignPadLength(c.ctxt, p.Pc, alignedValue)
                        for i = 0; i < int(v/4); i++ {
                                // emit ANOOP instruction by the padding size
                                c.ctxt.Arch.ByteOrder.PutUint32(bp, OP_NOOP)