From: Nathan Chancellor <nathan@kernel.org> To: ndesaulniers@google.com Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>, Maxime Ripard <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>, David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>, Tom Rix <trix@redhat.com>, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Naresh Kamboju <naresh.kamboju@linaro.org>, christian.koenig@amd.com, boris.brezillon@collabora.com, dakr@redhat.com, alexander.deucher@amd.com Subject: Re: [PATCH v2] drm: fix indirect goto into statement expression UB Date: Fri, 28 Jul 2023 10:17:57 -0700 [thread overview] Message-ID: <20230728171757.GA433645@dev-arch.thelio-3990X> (raw) In-Reply-To: <20230727-amdgpu-v2-1-7fc66bc52bf6@google.com> + people from trailers of 09593216bff1 On Thu, Jul 27, 2023 at 03:50:58PM -0700, ndesaulniers@google.com wrote: > A new diagnostic in clang-17 now produces the following build error: > > drivers/gpu/drm/tests/drm_exec_test.c:41:3: error: cannot jump from this > indirect goto statement to one of its possible targets > 41 | drm_exec_retry_on_contention(&exec); > | ^ > include/drm/drm_exec.h:96:4: note: expanded from macro > 'drm_exec_retry_on_contention' > 96 | goto *__drm_exec_retry_ptr; > | ^ > drivers/gpu/drm/tests/drm_exec_test.c:39:2: note: possible target of > indirect goto statement > 39 | drm_exec_until_all_locked(&exec) { > | ^ > include/drm/drm_exec.h:79:33: note: expanded from macro > 'drm_exec_until_all_locked' > 79 | __label__ __drm_exec_retry; > drivers/gpu/drm/tests/drm_exec_test.c:39:2: note: jump enters a > statement expression > > The GCC manually currently states that: ^ manual > >> Jumping into a statement expression with a computed goto (see Labels > >> as Values) has undefined behavior. > > So the diagnostic appears correct, even if codegen happened to produce > working code. > > Looking closer at this code, while the original combination of statement > expression, local label, and computed/indirect goto GNU C expressions > were clever, a simple while loop and continue block might have sufficed. > > This approach might not work as expected if drm_exec_until_all_locked > "loops" can be nested, but that doesn't appear to be an existing use > case in the codebase. > > Fixes: commit 09593216bff1 ("drm: execution context for GEM buffers v7") > Link: https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html > Link: https://github.com/ClangBuiltLinux/linux/issues/1890 > Link: https://github.com/llvm/llvm-project/commit/20219106060208f0c2f5d096eb3aed7b712f5067 > Reported-by: Nathan Chancellor <nathan@kernel.org> > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Thanks for the patch! Tested-by: Nathan Chancellor <nathan@kernel.org> # build > --- > Changes in v2: > Fix the continue to be outside of the do while > - Link to v1: https://lore.kernel.org/r/20230727-amdgpu-v1-1-a95690e75388@google.com > --- > include/drm/drm_exec.h | 21 +++++---------------- > 1 file changed, 5 insertions(+), 16 deletions(-) > > diff --git a/include/drm/drm_exec.h b/include/drm/drm_exec.h > index 73205afec162..fa1cc5c3d021 100644 > --- a/include/drm/drm_exec.h > +++ b/include/drm/drm_exec.h > @@ -70,18 +70,8 @@ struct drm_exec { > * Core functionality of the drm_exec object. Loops until all GEM objects are > * locked and no more contention exists. At the beginning of the loop it is > * guaranteed that no GEM object is locked. > - * > - * Since labels can't be defined local to the loops body we use a jump pointer > - * to make sure that the retry is only used from within the loops body. > */ > -#define drm_exec_until_all_locked(exec) \ > - for (void *__drm_exec_retry_ptr; ({ \ > - __label__ __drm_exec_retry; \ > -__drm_exec_retry: \ > - __drm_exec_retry_ptr = &&__drm_exec_retry; \ > - (void)__drm_exec_retry_ptr; \ > - drm_exec_cleanup(exec); \ > - });) > +#define drm_exec_until_all_locked(exec) while(drm_exec_cleanup(exec)) > > /** > * drm_exec_retry_on_contention - restart the loop to grap all locks > @@ -90,11 +80,10 @@ __drm_exec_retry: \ > * Control flow helper to continue when a contention was detected and we need to > * clean up and re-start the loop to prepare all GEM objects. > */ > -#define drm_exec_retry_on_contention(exec) \ > - do { \ > - if (unlikely(drm_exec_is_contended(exec))) \ > - goto *__drm_exec_retry_ptr; \ > - } while (0) > +#define drm_exec_retry_on_contention(exec) \ > + if (unlikely(drm_exec_is_contended(exec))) \ > + continue; \ > + do {} while (0) > > /** > * drm_exec_is_contended - check for contention > > --- > base-commit: 451cc82bd11eb6a374f4dbcfc1cf007eafea91ab > change-id: 20230727-amdgpu-93c0e5302951 > > Best regards, > -- > Nick Desaulniers <ndesaulniers@google.com> >
WARNING: multiple messages have this Message-ID (diff)
From: Nathan Chancellor <nathan@kernel.org> To: ndesaulniers@google.com Cc: Thomas Zimmermann <tzimmermann@suse.de>, Tom Rix <trix@redhat.com>, Naresh Kamboju <naresh.kamboju@linaro.org>, llvm@lists.linux.dev, linux-kernel@vger.kernel.org, Maxime Ripard <mripard@kernel.org>, boris.brezillon@collabora.com, dakr@redhat.com, dri-devel@lists.freedesktop.org, alexander.deucher@amd.com, christian.koenig@amd.com Subject: Re: [PATCH v2] drm: fix indirect goto into statement expression UB Date: Fri, 28 Jul 2023 10:17:57 -0700 [thread overview] Message-ID: <20230728171757.GA433645@dev-arch.thelio-3990X> (raw) In-Reply-To: <20230727-amdgpu-v2-1-7fc66bc52bf6@google.com> + people from trailers of 09593216bff1 On Thu, Jul 27, 2023 at 03:50:58PM -0700, ndesaulniers@google.com wrote: > A new diagnostic in clang-17 now produces the following build error: > > drivers/gpu/drm/tests/drm_exec_test.c:41:3: error: cannot jump from this > indirect goto statement to one of its possible targets > 41 | drm_exec_retry_on_contention(&exec); > | ^ > include/drm/drm_exec.h:96:4: note: expanded from macro > 'drm_exec_retry_on_contention' > 96 | goto *__drm_exec_retry_ptr; > | ^ > drivers/gpu/drm/tests/drm_exec_test.c:39:2: note: possible target of > indirect goto statement > 39 | drm_exec_until_all_locked(&exec) { > | ^ > include/drm/drm_exec.h:79:33: note: expanded from macro > 'drm_exec_until_all_locked' > 79 | __label__ __drm_exec_retry; > drivers/gpu/drm/tests/drm_exec_test.c:39:2: note: jump enters a > statement expression > > The GCC manually currently states that: ^ manual > >> Jumping into a statement expression with a computed goto (see Labels > >> as Values) has undefined behavior. > > So the diagnostic appears correct, even if codegen happened to produce > working code. > > Looking closer at this code, while the original combination of statement > expression, local label, and computed/indirect goto GNU C expressions > were clever, a simple while loop and continue block might have sufficed. > > This approach might not work as expected if drm_exec_until_all_locked > "loops" can be nested, but that doesn't appear to be an existing use > case in the codebase. > > Fixes: commit 09593216bff1 ("drm: execution context for GEM buffers v7") > Link: https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html > Link: https://github.com/ClangBuiltLinux/linux/issues/1890 > Link: https://github.com/llvm/llvm-project/commit/20219106060208f0c2f5d096eb3aed7b712f5067 > Reported-by: Nathan Chancellor <nathan@kernel.org> > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Thanks for the patch! Tested-by: Nathan Chancellor <nathan@kernel.org> # build > --- > Changes in v2: > Fix the continue to be outside of the do while > - Link to v1: https://lore.kernel.org/r/20230727-amdgpu-v1-1-a95690e75388@google.com > --- > include/drm/drm_exec.h | 21 +++++---------------- > 1 file changed, 5 insertions(+), 16 deletions(-) > > diff --git a/include/drm/drm_exec.h b/include/drm/drm_exec.h > index 73205afec162..fa1cc5c3d021 100644 > --- a/include/drm/drm_exec.h > +++ b/include/drm/drm_exec.h > @@ -70,18 +70,8 @@ struct drm_exec { > * Core functionality of the drm_exec object. Loops until all GEM objects are > * locked and no more contention exists. At the beginning of the loop it is > * guaranteed that no GEM object is locked. > - * > - * Since labels can't be defined local to the loops body we use a jump pointer > - * to make sure that the retry is only used from within the loops body. > */ > -#define drm_exec_until_all_locked(exec) \ > - for (void *__drm_exec_retry_ptr; ({ \ > - __label__ __drm_exec_retry; \ > -__drm_exec_retry: \ > - __drm_exec_retry_ptr = &&__drm_exec_retry; \ > - (void)__drm_exec_retry_ptr; \ > - drm_exec_cleanup(exec); \ > - });) > +#define drm_exec_until_all_locked(exec) while(drm_exec_cleanup(exec)) > > /** > * drm_exec_retry_on_contention - restart the loop to grap all locks > @@ -90,11 +80,10 @@ __drm_exec_retry: \ > * Control flow helper to continue when a contention was detected and we need to > * clean up and re-start the loop to prepare all GEM objects. > */ > -#define drm_exec_retry_on_contention(exec) \ > - do { \ > - if (unlikely(drm_exec_is_contended(exec))) \ > - goto *__drm_exec_retry_ptr; \ > - } while (0) > +#define drm_exec_retry_on_contention(exec) \ > + if (unlikely(drm_exec_is_contended(exec))) \ > + continue; \ > + do {} while (0) > > /** > * drm_exec_is_contended - check for contention > > --- > base-commit: 451cc82bd11eb6a374f4dbcfc1cf007eafea91ab > change-id: 20230727-amdgpu-93c0e5302951 > > Best regards, > -- > Nick Desaulniers <ndesaulniers@google.com> >
next prev parent reply other threads:[~2023-07-28 17:18 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-07-27 22:50 [PATCH v2] drm: fix indirect goto into statement expression UB ndesaulniers 2023-07-27 22:50 ` ndesaulniers 2023-07-28 17:17 ` Nathan Chancellor [this message] 2023-07-28 17:17 ` Nathan Chancellor 2023-07-31 7:03 ` Boris Brezillon 2023-07-31 7:03 ` Boris Brezillon 2023-07-31 9:50 ` Christian König 2023-07-31 9:50 ` Christian König
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