| Message ID | 20220201190116.182415-1-drjones@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [kvm-unit-tests] arm64: Fix compiling with ancient compiler | expand |
On 01/02/2022 20.01, Andrew Jones wrote: > When compiling with an ancient compiler (gcc-4.8.5-36.el7_6.2.aarch64) > the build fails with > > lib/libcflat.a(alloc.o): In function `mult_overflow': > /home/drjones/kvm-unit-tests/lib/alloc.c:19: undefined reference to `__multi3' > > According to kernel commit fb8722735f50 ("arm64: support __int128 on > gcc 5+") GCC5+ will not emit __multi3 for __int128 multiplication, > so let's just fallback to the non-__int128 overflow check when we > use gcc versions older than 5. > > Signed-off-by: Andrew Jones <drjones@redhat.com> > --- > lib/alloc.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/lib/alloc.c b/lib/alloc.c > index f4266f5d064e..70228aa32c6c 100644 > --- a/lib/alloc.c > +++ b/lib/alloc.c > @@ -1,6 +1,7 @@ > #include "alloc.h" > #include "asm/page.h" > #include "bitops.h" > +#include <linux/compiler.h> > > void *malloc(size_t size) > { > @@ -13,7 +14,7 @@ static bool mult_overflow(size_t a, size_t b) > /* 32 bit system, easy case: just use u64 */ > return (u64)a * (u64)b >= (1ULL << 32); > #else > -#ifdef __SIZEOF_INT128__ > +#if defined(__SIZEOF_INT128__) && (!defined(__aarch64__) || GCC_VERSION >= 50000) > /* if __int128 is available use it (like the u64 case above) */ > unsigned __int128 res = a; > res *= b; I'd also be OK if we'd simply declare GCC compiler versions < 5 as unsupported ... but since it's an easy fix: Acked-by: Thomas Huth <thuth@redhat.com>
On Wed, Feb 02, 2022 at 06:19:46AM +0100, Thomas Huth wrote: > On 01/02/2022 20.01, Andrew Jones wrote: > > When compiling with an ancient compiler (gcc-4.8.5-36.el7_6.2.aarch64) > > the build fails with > > > > lib/libcflat.a(alloc.o): In function `mult_overflow': > > /home/drjones/kvm-unit-tests/lib/alloc.c:19: undefined reference to `__multi3' > > > > According to kernel commit fb8722735f50 ("arm64: support __int128 on > > gcc 5+") GCC5+ will not emit __multi3 for __int128 multiplication, > > so let's just fallback to the non-__int128 overflow check when we > > use gcc versions older than 5. > > > > Signed-off-by: Andrew Jones <drjones@redhat.com> > > --- > > lib/alloc.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/lib/alloc.c b/lib/alloc.c > > index f4266f5d064e..70228aa32c6c 100644 > > --- a/lib/alloc.c > > +++ b/lib/alloc.c > > @@ -1,6 +1,7 @@ > > #include "alloc.h" > > #include "asm/page.h" > > #include "bitops.h" > > +#include <linux/compiler.h> > > void *malloc(size_t size) > > { > > @@ -13,7 +14,7 @@ static bool mult_overflow(size_t a, size_t b) > > /* 32 bit system, easy case: just use u64 */ > > return (u64)a * (u64)b >= (1ULL << 32); > > #else > > -#ifdef __SIZEOF_INT128__ > > +#if defined(__SIZEOF_INT128__) && (!defined(__aarch64__) || GCC_VERSION >= 50000) > > /* if __int128 is available use it (like the u64 case above) */ > > unsigned __int128 res = a; > > res *= b; > > I'd also be OK if we'd simply declare GCC compiler versions < 5 as > unsupported ... but since it's an easy fix: I'd like to continue supporting this particular old compiler, because I only have one machine where I can run the unit tests with KVM AArch32, and on that machine I still have an old RHEL (RHEL7-Alt) installed. If it gets too difficult to support, then I'll try upgrading that machine's RHEL version or at least its compiler version. > > Acked-by: Thomas Huth <thuth@redhat.com> > Thanks, but I need a v2 since I just remembered clang. For v2, I see two options: 1) Just change the line as below and hope we don't need to worry about clang versions #if defined(__SIZEOF_INT128__) && (!defined(__aarch64__) || defined(__clang__) || GCC_VERSION >= 50000) 2) Replace lib/alloc.c's mult_overflow() with lib/linux/compiler.h's check_mul_overflow() (2) seems like the better choice except for the fact that it lazily doesn't implement a fallback for compilers which don't support the builtins (and that's older than GCC7.1). Do we care? Of course I could combine the two implementations if we really want that fallback and the cleanup. Thanks, drew
diff --git a/lib/alloc.c b/lib/alloc.c index f4266f5d064e..70228aa32c6c 100644 --- a/lib/alloc.c +++ b/lib/alloc.c @@ -1,6 +1,7 @@ #include "alloc.h" #include "asm/page.h" #include "bitops.h" +#include <linux/compiler.h> void *malloc(size_t size) { @@ -13,7 +14,7 @@ static bool mult_overflow(size_t a, size_t b) /* 32 bit system, easy case: just use u64 */ return (u64)a * (u64)b >= (1ULL << 32); #else -#ifdef __SIZEOF_INT128__ +#if defined(__SIZEOF_INT128__) && (!defined(__aarch64__) || GCC_VERSION >= 50000) /* if __int128 is available use it (like the u64 case above) */ unsigned __int128 res = a; res *= b;
When compiling with an ancient compiler (gcc-4.8.5-36.el7_6.2.aarch64) the build fails with lib/libcflat.a(alloc.o): In function `mult_overflow': /home/drjones/kvm-unit-tests/lib/alloc.c:19: undefined reference to `__multi3' According to kernel commit fb8722735f50 ("arm64: support __int128 on gcc 5+") GCC5+ will not emit __multi3 for __int128 multiplication, so let's just fallback to the non-__int128 overflow check when we use gcc versions older than 5. Signed-off-by: Andrew Jones <drjones@redhat.com> --- lib/alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)