| Message ID | 20190813120117.22528-1-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86/tss: Fix clang build following c/s 7888440625 | expand |
On Tue, Aug 13, 2019 at 01:01:17PM +0100, Andrew Cooper wrote: > Clang-3.5 from Debian Jessie fails with: > > smpboot.c:829:29: error: statement expression not allowed at file scope > BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE); > ^ > /local/xen.git/xen/include/asm/percpu.h:14:7: note: expanded from macro > 'this_cpu' > (*RELOC_HIDE(&per_cpu__##var, get_cpu_info()->per_cpu_offset)) > ^ > /local/xen.git/xen/include/xen/compiler.h:98:3: note: expanded from macro > 'RELOC_HIDE' > ({ unsigned long __ptr; \ > ^ > /local/xen.git/xen/include/xen/lib.h:26:53: note: expanded from macro > 'BUILD_BUG_ON' > #define BUILD_BUG_ON(cond) ((void)BUILD_BUG_ON_ZERO(cond)) > ^ > /local/xen.git/xen/include/xen/lib.h:25:57: note: expanded from macro > 'BUILD_BUG_ON_ZERO' > #define BUILD_BUG_ON_ZERO(cond) sizeof(struct { int:-!!(cond); }) > ^ > 1 error generated. > /local/xen.git/xen/Rules.mk:202: recipe for target 'smpboot.o' failed > > This is obviously a compiler bug because the BUILD_BUG_ON() is not at file > scope. However, it can be worked around by using a local variable. > > Spotted by Gitlab CI. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Wei Liu <wl@xen.org>
On 13.08.2019 14:01, Andrew Cooper wrote: > Clang-3.5 from Debian Jessie fails with: > > smpboot.c:829:29: error: statement expression not allowed at file scope > BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE); > ^ > /local/xen.git/xen/include/asm/percpu.h:14:7: note: expanded from macro > 'this_cpu' > (*RELOC_HIDE(&per_cpu__##var, get_cpu_info()->per_cpu_offset)) > ^ > /local/xen.git/xen/include/xen/compiler.h:98:3: note: expanded from macro > 'RELOC_HIDE' > ({ unsigned long __ptr; \ > ^ > /local/xen.git/xen/include/xen/lib.h:26:53: note: expanded from macro > 'BUILD_BUG_ON' > #define BUILD_BUG_ON(cond) ((void)BUILD_BUG_ON_ZERO(cond)) > ^ > /local/xen.git/xen/include/xen/lib.h:25:57: note: expanded from macro > 'BUILD_BUG_ON_ZERO' > #define BUILD_BUG_ON_ZERO(cond) sizeof(struct { int:-!!(cond); }) > ^ > 1 error generated. > /local/xen.git/xen/Rules.mk:202: recipe for target 'smpboot.o' failed > > This is obviously a compiler bug because the BUILD_BUG_ON() is not at file > scope. However, it can be worked around by using a local variable. It can be worked around, yes, but the result is not identical: > --- a/xen/arch/x86/smpboot.c > +++ b/xen/arch/x86/smpboot.c > @@ -826,9 +826,11 @@ static int setup_cpu_root_pgt(unsigned int cpu) > rc = clone_mapping(idt_tables[cpu], rpt); > if ( !rc ) > { > - BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE); > + struct tss_page *this_tss = &per_cpu(tss_page, cpu); Whatever type is compatible with struct tss_page * will now be permitted on the rhs. Hence ... > - rc = clone_mapping(&per_cpu(tss_page, cpu).tss, rpt); > + BUILD_BUG_ON(sizeof(*this_tss) != PAGE_SIZE); ... this sizeof() is not necessarily checking the size of the per-CPU variable. But anyway - the change has been committed already, and the chances of this going wrong are low enough, so please don't treat this as an objection or revert request. Jan
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c index 5057109a77..85c81c247e 100644 --- a/xen/arch/x86/smpboot.c +++ b/xen/arch/x86/smpboot.c @@ -826,9 +826,11 @@ static int setup_cpu_root_pgt(unsigned int cpu) rc = clone_mapping(idt_tables[cpu], rpt); if ( !rc ) { - BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE); + struct tss_page *this_tss = &per_cpu(tss_page, cpu); - rc = clone_mapping(&per_cpu(tss_page, cpu).tss, rpt); + BUILD_BUG_ON(sizeof(*this_tss) != PAGE_SIZE); + + rc = clone_mapping(&this_tss->tss, rpt); } if ( !rc ) rc = clone_mapping((void *)per_cpu(stubs.addr, cpu), rpt);
Clang-3.5 from Debian Jessie fails with: smpboot.c:829:29: error: statement expression not allowed at file scope BUILD_BUG_ON(sizeof(this_cpu(tss_page)) != PAGE_SIZE); ^ /local/xen.git/xen/include/asm/percpu.h:14:7: note: expanded from macro 'this_cpu' (*RELOC_HIDE(&per_cpu__##var, get_cpu_info()->per_cpu_offset)) ^ /local/xen.git/xen/include/xen/compiler.h:98:3: note: expanded from macro 'RELOC_HIDE' ({ unsigned long __ptr; \ ^ /local/xen.git/xen/include/xen/lib.h:26:53: note: expanded from macro 'BUILD_BUG_ON' #define BUILD_BUG_ON(cond) ((void)BUILD_BUG_ON_ZERO(cond)) ^ /local/xen.git/xen/include/xen/lib.h:25:57: note: expanded from macro 'BUILD_BUG_ON_ZERO' #define BUILD_BUG_ON_ZERO(cond) sizeof(struct { int:-!!(cond); }) ^ 1 error generated. /local/xen.git/xen/Rules.mk:202: recipe for target 'smpboot.o' failed This is obviously a compiler bug because the BUILD_BUG_ON() is not at file scope. However, it can be worked around by using a local variable. Spotted by Gitlab CI. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Jan Beulich <JBeulich@suse.com> CC: Wei Liu <wl@xen.org> CC: Roger Pau Monné <roger.pau@citrix.com> --- xen/arch/x86/smpboot.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)