On Nov 25, 2020, at 20:17, Borislav Petkov [off-list ref] wrote:

On Thu, Nov 19, 2020 at 11:02:34AM -0800, Chang S. Bae wrote:

quoted

diff --git a/arch/x86/include/asm/sigframe.h b/arch/x86/include/asm/sigframe.h
index 84eab2724875..ac77f3f90bc9 100644
--- a/arch/x86/include/asm/sigframe.h
+++ b/arch/x86/include/asm/sigframe.h

@@ -52,6 +52,15 @@ struct rt_sigframe_ia32 {

	char retcode[8];
	/* fp state follows here */
};
+
+#define SIZEOF_sigframe_ia32	sizeof(struct sigframe_ia32)
+#define SIZEOF_rt_sigframe_ia32	sizeof(struct rt_sigframe_ia32)
+
+#else
+
+#define SIZEOF_sigframe_ia32	0
+#define SIZEOF_rt_sigframe_ia32	0
+
#endif /* defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) */

#ifdef CONFIG_X86_64

@@ -81,8 +90,22 @@ struct rt_sigframe_x32 {

	/* fp state follows here */
};

+#define SIZEOF_rt_sigframe_x32	sizeof(struct rt_sigframe_x32)
+
#endif /* CONFIG_X86_X32_ABI */

+#define SIZEOF_rt_sigframe	sizeof(struct rt_sigframe)
+
+#else
+
+#define SIZEOF_rt_sigframe	0
+
#endif /* CONFIG_X86_64 */

+#ifndef SIZEOF_rt_sigframe_x32
+#define SIZEOF_rt_sigframe_x32	0
+#endif

Those are defined here to be used in only one place -
init_sigframe_size() - where there already is ifdeffery. Just use the
normal sizeof() operator there instead of adding more gunk here.

[ Just want to clarify your comment. ]

Admittedly, this is an (ugly) workaround to avoid compile errors.

E.g. when code is written like this in the function:

	if (IS_ENABLED(CONFIG_X86_X32_ABI))
		size = max(size, sizeof(struct rt_sigframe_x32));

and compile with CONFIG_X86_X32_ABI=n, got such a message:

	"invalid application of 'sizeof' to incomplete type 'struct
	sigframe_ia32’"

While the coding-style doc [1] seems to mention this:

   "However, this approach still allows the C compiler to see the
    code inside the block, and check it for correctness (syntax, 
    types, symbol references, etc). Thus, you still have to use an 
    #ifdef if the code inside the block references symbols that 
    will not exist if the condition is not met.”

In general, putting #ifdef in a C file is advised to avoid. I wonder
whether it is okay to include #ifdef in the C file in this case.

Thanks,
Chang

[1] https://www.kernel.org/doc/html/v5.9/process/coding-style.html