Re: [PATCH v4 6/9] x86: prevent inline distortion by paravirt ops

On 12/06/18 13:50, Nadav Amit wrote:

GCC considers the number of statements in inlined assembly blocks,
according to new-lines and semicolons, as an indication to the cost of
the block in time and space. This data is distorted by the kernel code,
which puts information in alternative sections. As a result, the
compiler may perform incorrect inlining and branch optimizations.

The solution is to set an assembly macro and call it from the inlined
assembly block. As a result GCC considers the inline assembly block as
a single instruction.

The effect of the patch is a more aggressive inlining, which also
causes a size increase of kernel.

   text	   data	    bss	    dec	    hex	filename
18147336 10226688 2957312 31331336 1de1408 ./vmlinux before
18162555 10226288 2957312 31346155 1de4deb ./vmlinux after (+14819)

Static text symbols:
Before:	40053
After:	39942	(-111)

Cc: Juergen Gross <jgross@suse.com>
Cc: Alok Kataria <redacted>
Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: virtualization@lists.linux-foundation.org

Signed-off-by: Nadav Amit <redacted>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen