Re: [Libguestfs] [nbdkit] [filter/nozero] large binary size with GCC 9

On 7/4/19 1:38 PM, Thomas Weißschuh wrote: Thanks for the pointers. Odd that you are only seeing this for the nozero filter, since we also have the same sort of buffer in server/plugins.c. Oh, I see a difference between the two - one is function-local, the other is file-local. Does this patch make a difference? (I need to fire up a rawhide VM to test it myself...) If it doesn't, then removing the 'const' seems like the easiest trick to work around this compiler pessimization (yes, I can see why the compiler writers argued that sticking things in .rodata adds a bit more security against errant code accidentally trying to corrupt the buffer; but as the buffer shouldn't be escaping, it's already undefined behavior for such code to happen). diff --git i/filters/nozero/nozero.c w/filters/nozero/nozero.c index 16ec710b..21863707 100644 --- i/filters/nozero/nozero.c +++ w/filters/nozero/nozero.c @@ -45,7 +45,6 @@ #define MAX_WRITE (64 * 1024 * 1024) -static const char buffer[MAX_WRITE]; static enum ZeroMode { NONE, EMULATE, @@ -111,6 +110,8 @@ nozero_zero (struct nbdkit_next_ops *next_ops, void *nxdata, while (count) { uint32_t size = MIN (count, MAX_WRITE); + static const char buffer[MAX_WRITE]; /* Always contains zeroes */ + if (next_ops->pwrite (nxdata, buffer, size, offs, flags, err) == -1) return -1; offs += size; -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org