[PATCH v2 01/71] cocci/rte_memcpy: add script to eliminate fixed size rte_memcpy

[Stephen Hemminger]

On Sat, 2 Mar 2024 12:19:13 +0100
Mattias Rönnblom <hofors at lysator.liu.se> wrote:

> On 2024-03-01 18:14, Stephen Hemminger wrote:
> > Rte_memcpy should not be used for the simple case of copying
> > a fix size structure because it is slower and will hide problems
> > from code analysis tools. Coverity, fortify and other analyzers
> > special case memcpy().
> > 
> > Gcc (and Clang) are smart enough to inline copies which
> > will be faster.
> >   
> 
> Are you suggesting rte_memcpy() calls aren't inlined?

With a simple made up example of copying an IPv6 address.

rte_memcpy() inlines to:
rte_copy_addr:
        movdqu  xmm0, XMMWORD PTR [rsi]
        movups  XMMWORD PTR [rdi], xmm0
        movdqu  xmm0, XMMWORD PTR [rsi]
        movups  XMMWORD PTR [rdi], xmm0
        ret

Vs memcpy becomes.

copy_addr:
        movdqu  xmm0, XMMWORD PTR [rsi]
        movups  XMMWORD PTR [rdi], xmm0
        ret

Looks like a bug in rte_memcpy_generic? Why is it not handling
16 bytes correctly.

For me, it was more about getting fortify and compiler warnings to
catch bugs. For most code, the output should be the same.