[Qemu-devel] [PATCH v2] configure: Make epoll_create1 test work around SPARC glibc bug

[Qemu-devel] [PATCH v2] configure: Make epoll_create1 test work around SPARC glibc bug

[Peter Maydell]

Work around a SPARC glibc bug which caused the epoll_create1 configure
test to wrongly claim that the function was present. Some versions of
SPARC glibc provided the function in the library but didn't declare
it in the include file; the result is that gcc warns about an implicit
declaration but a link succeeds. So we reference the function as a
value rather than a function call to induce a compile time error
if the declaration was not present.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
v1->v2: instead of compiling the test with -Werror, use the approach
suggested by Blue Swirl to force a compile-time failure if the
declaration is missing from the header file.

 configure |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/configure b/configure
index de44bac..2bbbbf5 100755
--- a/configure
+++ b/configure
@@ -2225,7 +2225,15 @@ cat > $TMPC << EOF
 
 int main(void)
 {
-    epoll_create1(0);
+    /* Note that we use epoll_create1 as a value, not as
+     * a function being called. This is necessary so that on
+     * old SPARC glibc versions where the function was present in
+     * the library but not declared in the header file we will
+     * fail the configure check. (Otherwise we will get a compiler
+     * warning but not an error, and will proceed to fail the
+     * qemu compile where we compile with -Werror.)
+     */
+    epoll_create1;
     return 0;
 }
 EOF
-- 
1.7.1

Re: [Qemu-devel] [PATCH v2] configure: Make epoll_create1 test work around SPARC glibc bug

[Blue Swirl]

Thanks, applied.

On Tue, Apr 26, 2011 at 6:56 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> Work around a SPARC glibc bug which caused the epoll_create1 configure
> test to wrongly claim that the function was present. Some versions of
> SPARC glibc provided the function in the library but didn't declare
> it in the include file; the result is that gcc warns about an implicit
> declaration but a link succeeds. So we reference the function as a
> value rather than a function call to induce a compile time error
> if the declaration was not present.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> v1->v2: instead of compiling the test with -Werror, use the approach
> suggested by Blue Swirl to force a compile-time failure if the
> declaration is missing from the header file.
>
>  configure |   10 +++++++++-
>  1 files changed, 9 insertions(+), 1 deletions(-)
>
> diff --git a/configure b/configure
> index de44bac..2bbbbf5 100755
> --- a/configure
> +++ b/configure
> @@ -2225,7 +2225,15 @@ cat > $TMPC << EOF
>
>  int main(void)
>  {
> -    epoll_create1(0);
> +    /* Note that we use epoll_create1 as a value, not as
> +     * a function being called. This is necessary so that on
> +     * old SPARC glibc versions where the function was present in
> +     * the library but not declared in the header file we will
> +     * fail the configure check. (Otherwise we will get a compiler
> +     * warning but not an error, and will proceed to fail the
> +     * qemu compile where we compile with -Werror.)
> +     */
> +    epoll_create1;
>     return 0;
>  }
>  EOF
> --
> 1.7.1
>
>