Re: [PULL 09/16] memory: add a sparse memory device for fuzzing

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/16/21 10:15 PM, Paolo Bonzini wrote:
> From: Alexander Bulekov <alxndr@bu.edu>
> 
> For testing, it can be useful to simulate an enormous amount of memory
> (e.g. 2^64 RAM). This adds an MMIO device that acts as sparse memory.
> When something writes a nonzero value to a sparse-mem address, we
> allocate a block of memory. For now, since the only user of this device
> is the fuzzer, we do not track and free zeroed blocks. The device has a
> very low priority (so it can be mapped beneath actual RAM, and virtual
> device MMIO regions).
> 
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  MAINTAINERS                 |   1 +
>  hw/mem/meson.build          |   1 +
>  hw/mem/sparse-mem.c         | 151 ++++++++++++++++++++++++++++++++++++
>  include/hw/mem/sparse-mem.h |  19 +++++
>  4 files changed, 172 insertions(+)
>  create mode 100644 hw/mem/sparse-mem.c
>  create mode 100644 include/hw/mem/sparse-mem.h

> diff --git a/hw/mem/meson.build b/hw/mem/meson.build
> index 0d22f2b572..ef79e04678 100644
> --- a/hw/mem/meson.build
> +++ b/hw/mem/meson.build
> @@ -1,5 +1,6 @@
>  mem_ss = ss.source_set()
>  mem_ss.add(files('memory-device.c'))
> +mem_ss.add(when: 'CONFIG_FUZZ', if_true: files('sparse-mem.c'))
>  mem_ss.add(when: 'CONFIG_DIMM', if_true: files('pc-dimm.c'))
>  mem_ss.add(when: 'CONFIG_NPCM7XX', if_true: files('npcm7xx_mc.c'))
>  mem_ss.add(when: 'CONFIG_NVDIMM', if_true: files('nvdimm.c'))

Completing the diff:

>
>  softmmu_ss.add_all(when: 'CONFIG_MEM_DEVICE', if_true: mem_ss)

There is a problem when MEM_DEVICE is not selected, sparse-mem
is not linked (even if CONFIG_FUZZ is selected):

tests/qtest/fuzz/generic_fuzz.c:826: undefined reference to
`sparse_mem_init'
clang-10: error: linker command failed with exit code 1 (use -v to see
invocation)

Easy fix:

-- >8 --
--- a/hw/mem/meson.build
+++ b/hw/mem/meson.build
@@ -1,8 +1,9 @@
 mem_ss = ss.source_set()
 mem_ss.add(files('memory-device.c'))
 mem_ss.add(when: 'CONFIG_FUZZ', if_true: files('sparse-mem.c'))
-mem_ss.add(when: 'CONFIG_DIMM', if_true: files('pc-dimm.c'))
 mem_ss.add(when: 'CONFIG_NPCM7XX', if_true: files('npcm7xx_mc.c'))
 mem_ss.add(when: 'CONFIG_NVDIMM', if_true: files('nvdimm.c'))

 softmmu_ss.add_all(when: 'CONFIG_MEM_DEVICE', if_true: mem_ss)
+
+softmmu_ss.add(when: 'CONFIG_FUZZ', if_true: files('sparse-mem.c'))
---

Patch coming.