michael_d writes in #1874:

On an i386 platform with no rt_sigsuspend syscall (ie: Linux 2.0), compilation will halt on libc/sysdeps/linux/common/sigsuspend.os with a cryptic error message:
"Error: non-constant expression in ".if" statement"

I've investigated and found that the cause is that a literal '0' is being passed into a block of complex assembler macrology that is only prepared to deal with register names - '%eax', etc.

In turn, that seems to be because of a typo in the GCC register constraints. The constraints for 2 and 3-argument syscalls includes a "C" constraint. To gcc, "C" means an SSE floating point constant -- an unlikely element in a syscall. I suspect the author meant to type "S" (%esi).

diff --git a/libc/sysdeps/linux/i386/bits/syscalls.h b/libc/sysdeps/linux/i386/bits/syscalls.h
index 8b2f1b0..15cd9f3 100644 (file)
--- a/libc/sysdeps/linux/i386/bits/syscalls.h
+++ b/libc/sysdeps/linux/i386/bits/syscalls.h
@@ -197,9 +197,9 @@ return (type) (INLINE_SYSCALL(name, 6, arg1, arg2, arg3, arg4, arg5, arg6)); \
 #define ASMFMT_1(arg1) \
        , "acdSD" (arg1)
 #define ASMFMT_2(arg1, arg2) \
-       , "adCD" (arg1), "c" (arg2)
+       , "adSD" (arg1), "c" (arg2)
 #define ASMFMT_3(arg1, arg2, arg3) \
-       , "aCD" (arg1), "c" (arg2), "d" (arg3)
+       , "aSD" (arg1), "c" (arg2), "d" (arg3)
 #define ASMFMT_4(arg1, arg2, arg3, arg4) \
        , "aD" (arg1), "c" (arg2), "d" (arg3), "S" (arg4)
 #define ASMFMT_5(arg1, arg2, arg3, arg4, arg5) \