Thanks! Didn't know that the assembler is able to do this. TBH, for me, it's not desired behaviour when an assembler program does something extra to a low-level code. I have already observed that Go asm strips a series of NOPs, which is highly unexpected.
A directive for alignment is way clearer. Not to mention that sometimes we don't need to align jump targets. w. On Friday, February 25, 2022 at 9:35:10 AM UTC+1 Brian Candler wrote: > It seems to me that there is automatic alignment for loops: > > https://github.com/golang/go/blob/go1.17.7/src/cmd/internal/obj/x86/asm6.go#L51-L67 > > > On Friday, 25 February 2022 at 06:42:23 UTC Wojciech Muła wrote: > >> The directive is not documented on >> https://pkg.go.dev/cmd/internal/obj/x86. `grep -l -R PCALIGN *` run in >> `cmd/interal/obj` shows for the freshest master: >> >> arm64/doc.go >> arm64/asm7.go >> arm64/asm_arm64_test.go >> link.go >> ppc64/doc.go >> ppc64/asm9.go >> ppc64/asm_test.go >> util.go >> >> Seems it's not implemented. When tried to use it, I got the following >> error: >> >> # main >> asm: asmins: missing op 00000 (<unknown line number>) PCALIGN >> $16 >> asm: assembly failed >> >> Sample asm code to check this: >> >> ---asmfun_amd64.s--- >> #include "textflag.h" >> >> TEXT ·asmfun(SB), NOSPLIT, $0 >> PCALIGN $16 >> RET >> ---eof--- >> >> ---main.go--- >> package main >> >> // go:noescape >> func asmfun() >> func main() { asmfun() } >> ---eof--- >> >> w. >> >> On Friday, February 25, 2022 at 2:21:41 AM UTC+1 Ian Lance Taylor wrote: >> >>> On Thu, Feb 24, 2022 at 9:40 AM Wojciech Muła <wojte...@gmail.com> >>> wrote: >>> > >>> > I'm writing an implementation in x86 assembler and I need to force a >>> certain alignment of blocks of code (as it affects performance). I found >>> that there's PCALIGN directive, but it's only available for the PPC >>> architecture. It does not work for x86. >>> > >>> > Is there any easy way to achieve this for x86? If I had one loop, it >>> won't be a problem --- I'd just put a few `BYTE $0x90` and move on. The >>> problem is my code is huge, partially autogenerated with few variants. >>> > >>> > Any hints? >>> >>> As far as I can tell PCALIGN is implemented for all architectures. >>> >>> Ian >>> >> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/c6821872-a99d-45af-b119-6b56bdd0fd3cn%40googlegroups.com.
