From: Lucas Gabriel Vuotto <lucas@sexy.is>
Subject: Re: exec_elf.h: remove CONCAT definition
To: tech@openbsd.org
Date: Tue, 15 Apr 2025 09:02:16 +0000

On Tue, Apr 15, 2025 at 06:34:00AM +0000, Lucas Gabriel Vuotto wrote:
> Hi tech,
> 
> /sys/sys/exec_elf.h defines a CONCAT macro as another name for __CONCAT
> and uses it in the next 2 lines:
> 
>    751	#if defined(ELFSIZE)
>    752	#define CONCAT(x,y)	__CONCAT(x,y)
>    753	#define ELFNAME(x)	CONCAT(elf,CONCAT(ELFSIZE,CONCAT(_,x)))
>    754	#define ELFDEFNNAME(x)	CONCAT(ELF,CONCAT(ELFSIZE,CONCAT(_,x)))
>    755	#endif
> 
> CONCAT tends to be commonly used for this same purpouse, and this header
> can leak into public. In src tree, CONCAT is defined in:
> 
> /usr/src/gnu/gcc/gcc/config/sh/lib1funcs.h
> /usr/src/gnu/llvm/lldb/tools/debugserver/source/RNBDefs.h
> /usr/src/gnu/usr.bin/gcc/gcc/config/sh/lib1funcs.asm
> /usr/src/gnu/usr.bin/gcc/gcc/testsuite/gcc.dg/attr-invalid.c
> /usr/src/usr.bin/make/defines.h
> 
> In ports land, at least net/haproxy defines CONCAT. It's also used as
> the name on some resources online.
> 
> Given that it's a common, and that its definition in exec_elf.h isn't
> really doing anything, OK to unroll it? I built a kernel successfully;
> idk if there is another thing I should take a care a look for. Release?
> Ask for a bulk?

tb helpfully started a bulk for me, which died quite quickly while
building /sys/arch/amd64/stand/boot: The definition of CONCAT is needed
because a macro doesn't expand itself in its definition. Undefining
CONCAT isn't an option neither, as the expansion happens way later. I
still think that CONCAT is a too generic name for a public header, so I
propose renaming it to ELFCONCAT.


diff refs/heads/master acf5035294bd686b67df0f4fa089e9fa32827a87
commit - fe0564919a5ad48e136b44be6d5be4142f626e37
commit + acf5035294bd686b67df0f4fa089e9fa32827a87
blob - 4781824b4fa893f68921f4e36226bc72cca6cb06
blob + e67f7e16f697b4b64c2d6ec8ad18cc8a9c2f8496
--- sys/sys/exec_elf.h
+++ sys/sys/exec_elf.h
@@ -749,9 +749,9 @@ struct elf_args {
 #endif
 
 #if defined(ELFSIZE)
-#define CONCAT(x,y)	__CONCAT(x,y)
-#define ELFNAME(x)	CONCAT(elf,CONCAT(ELFSIZE,CONCAT(_,x)))
-#define ELFDEFNNAME(x)	CONCAT(ELF,CONCAT(ELFSIZE,CONCAT(_,x)))
+#define ELFCONCAT(a,b)	__CONCAT(a,b)
+#define ELFNAME(x)	ELFCONCAT(elf,ELFCONCAT(ELFSIZE,ELFCONCAT(_,x)))
+#define ELFDEFNNAME(x)	ELFCONCAT(ELF,ELFCONCAT(ELFSIZE,ELFCONCAT(_,x)))
 #endif
 
 #if defined(ELFSIZE) && (ELFSIZE == 32)