Re: [PATCH] qemu/atomic.h: prefix qemu_ to solve <stdatomic.h> collisions

[Eric Blake]

On 9/21/20 11:23 AM, Stefan Hajnoczi wrote:
> clang's C11 atomic_fetch_*() functions only take a C11 atomic type
> pointer argument. QEMU uses direct types (int, etc) and this causes a
> compiler error when a QEMU code calls these functions in a source file
> that also included <stdatomic.h> via a system header file:
>
>    $ CC=clang CXX=clang++ ./configure ... && make
>    ../util/async.c:79:17: error: address argument to atomic operation must be a 
> pointer to _Atomic type ('unsigned int *' invalid)
>
> Avoid using atomic_*() names in QEMU's atomic.h since that namespace is
> used by <stdatomic.h>. Prefix QEMU's APIs with qemu_ so that atomic.h
> and <stdatomic.h> can co-exist.
>
> This patch was generated using:
>
>    $ git diff | grep -o '\<atomic_[a-z0-9_]\+' | sort -u 
> >/tmp/changed_identifiers

Missing a step in the recipe: namely, you probably modified 
include/qemu/atomic*.h prior to running 'git diff' (so that you actually 
had input to feed to grep -o).  But spelling it 'git diff HEAD^ 
include/qemu/atomic*.h | ...' does indeed give me a sane list of 
identifiers that looks like what you touched in the rest of the patch.

>    $ for identifier in $(</tmp/changed_identifiers64); do \

Also not quite the right recipe, based on the file name used in the line 
above.

>         sed -i "s%\<$identifier\>%qemu_$identifier%" $(git grep -l 
> "\<$identifier\>") \
>      done

Fortunately, running "git grep -c '\<atomic_[a-z0-9_]\+'" on the 
pre-patch state of the tree gives me a list that is somewhat close to 
yours, where the obvious difference in line counts is explained by:

> I manually fixed line-wrap issues and misaligned rST tables.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---

First, focusing on the change summary:

>   docs/devel/lockcnt.txt                        |  14 +-
>   docs/devel/rcu.txt                            |  40 +--
>   accel/tcg/atomic_template.h                   |  20 +-
>   include/block/aio-wait.h                      |   4 +-
>   include/block/aio.h                           |   8 +-
>   include/exec/cpu_ldst.h                       |   2 +-
>   include/exec/exec-all.h                       |   6 +-
>   include/exec/log.h                            |   6 +-
>   include/exec/memory.h                         |   2 +-
>   include/exec/ram_addr.h                       |  27 +-
>   include/exec/ramlist.h                        |   2 +-
>   include/exec/tb-lookup.h                      |   4 +-
>   include/hw/core/cpu.h                         |   2 +-
>   include/qemu/atomic.h                         | 258 +++++++-------
>   include/qemu/atomic128.h                      |   6 +-

These two are the most important for the sake of this patch; perhaps 
it's worth a temporary override of your git orderfile if you have to 
respin, to list them first?

>   include/qemu/bitops.h                         |   2 +-
>   include/qemu/coroutine.h                      |   2 +-
>   include/qemu/log.h                            |   6 +-
>   include/qemu/queue.h                          |   8 +-
>   include/qemu/rcu.h                            |  10 +-
>   include/qemu/rcu_queue.h                      | 103 +++---

Presumably, this and any other file with an odd number of changes was 
due to a difference in lines after reformatting long lines.

>   include/qemu/seqlock.h                        |   8 +-
...

>   util/stats64.c                                |  34 +-
>   docs/devel/atomics.rst                        | 326 +++++++++---------
>   .../opensbi-riscv32-generic-fw_dynamic.elf    | Bin 558668 -> 558698 bytes
>   .../opensbi-riscv64-generic-fw_dynamic.elf    | Bin 620424 -> 620454 bytes

Why are we regenerating .elf files in this patch?  Is your change even 
correct for those two files?

>   scripts/kernel-doc                            |   2 +-
>   tcg/aarch64/tcg-target.c.inc                  |   2 +-
>   tcg/mips/tcg-target.c.inc                     |   2 +-
>   tcg/ppc/tcg-target.c.inc                      |   6 +-
>   tcg/sparc/tcg-target.c.inc                    |   5 +-
>   135 files changed, 1195 insertions(+), 1130 deletions(-)

I don't spot accel/tcg/atomic_common.c.inc in the list (which declares 
functions such as atomic_trace_rmw_pre) - I guess that's intentional 
based on how you tried to edit only the identifiers you touched in 
include/qemu/atomic*.h.

For the rest of this patch, I only spot-checked in places, trusting the 
mechanical nature of this patch, and not spotting anything wrong in the 
places I checked.  But the two .elf files worry me enough to withhold 
R-b.  At the same time, because it's big, it will probably be a source 
of conflicts if we don't get it in soon, but can also be regenerated (if 
your recipe is corrected) without too much difficulty.  So I am in favor 
of the idea.

> diff --git a/pc-bios/opensbi-riscv32-generic-fw_dynamic.elf 
> b/pc-bios/opensbi-riscv32-generic-fw_dynamic.elf
> index 
> eb9ebf5674d3953ab25de6bf4db134abe904eb20..35b80512446dcf5c49424ae90caacf3c579be1b5
>  100644
> GIT binary patch
> delta 98
> zcmX@pqx7mrsiB3jg{g(Pg=Gt?!4uZP)ZEhe?LdZ@5QIJ5?Hg+mgxS918!HgAZQt>Y
> ceSHN~X?i|K5fhYsvykI97nHrFhGPaN0Hp#a^8f$<
>
> delta 62
> zcmaFWqjaW6siB3jg{g(Pg=Gt?!ISN#Pguo-rU!guEowjhjTMO5wjck-zP@66bv{QC
> S)Amn=9Jjf)U#j7l!3h9Zj2qGb
>
> diff --git a/pc-bios/opensbi-riscv64-generic-fw_dynamic.elf 
> b/pc-bios/opensbi-riscv64-generic-fw_dynamic.elf
> index 
> 642a64e240d09b2ddb9fc12c74718ae8d386b9d3..9cf2cf23b747cb5be1d3389a0611d8697609c6f8
>  100644
> GIT binary patch
> delta 102
> zcmeBpue$8LYC{WS3sVbo3(FSPMGsgDQ*%q>w*wh6LJ;=!eV<s1Ak21y&#XYq2E^>!
> e4L)<s&w(mGAJ19D1Z6uWaUSP_vN>`&8@K>*RVYvZ
>
> delta 66
> zcmZ4XUbW-BYC{WS3sVbo3(FSPMGv+wf50juH2uUU)}nU%&#XYq2E^>!?LTwO&)NPs
> Up0kK)dsGtVajxxZxttAL0Np<vJ^%m!
>
> diff --git a/scripts/kernel-doc b/scripts/kernel-doc
> index 030b5c8691..9ec38a1bf1 100755
> --- a/scripts/kernel-doc
> +++ b/scripts/kernel-doc
> @@ -1625,7 +1625,7 @@ sub dump_function($$) {
>       # If you mess with these regexps, it's a good idea to check that
>       # the following functions' documentation still comes out right:
>       # - parport_register_device (function pointer parameters)
> -    # - atomic_set (macro)
> +    # - qemu_atomic_set (macro)
>       # - pci_match_device, __copy_to_user (long return type)

Does the result of sphinx still look good, as mentioned in this comment?

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org