On 07/18/2017 06:33 PM, Jonathan Wakely wrote:
On 18 July 2017 at 21:46, Dennis Clarke wrote:
Fascinating. I never would have thought that a zero line length file
would be accepted as valid. However gcc ( older rev 4.9.2 ) will
accept this :
$ printf "int main ( int argc, char* argv[] ) { return 0; }" > tzero.c
Aside: why would you bother to declare parameters for such a program?
What's wrong with int main(void) ?
I wonder about this every time somebody reports a bug that gives
-Wunused-parameter warnings because of pointless unused parameters.
Since C99 (and in C++) you don't even need the return statement.
int main() { }
Not interested in "-Wunused-parameter" issues. I think you missed the
point. Regardless here :
0000000 69 6e 74 20 6d 61 69 6e 20 28 29 20 7b 20 72 65
i n t m a i n ( ) { r e
0000010 74 75 72 6e 20 37 3b 20 7d
t u r n 7 ; }
GCC compiles that fine and the output assembly :
------------------ output assembly ----------------------
1 .file "tzero.c"
2 .section ".text"
3 .align 4
4 .global main
5 .type main, #function
6 .proc 04
7 main:
8 save %sp, -176, %sp
9 mov 7, %g1
10 sra %g1, 0, %g1
11 mov %g1, %i0
12 return %i7+8
13 nop
14 .size main, .-main
15 .ident "GCC: (genunix Fri Jan 2 11:56:03 GMT 2015) 4.9.2"
-----------------------------------------------------------
Oracle Studio 12.4 rejects the input file as invalid :
"tzero.c", line 1: warning: newline not last character in file
However the assembler is happy with the asm source above :
tzero: ELF 64-bit MSB executable SPARCV9 Version 1, UltraSPARC1
Extensions Required, dynamically linked, not stripped, no debugging
information available
Let's execute that binary and check the return val
$ ./tzero
$ echo $?
7
Is there a diff at all regardless of the parameters for the func main?
Not much.
Consider this :
-----------------------------------------------------------
0000000 69 6e 74 20 6d 61 69 6e 20 28 20 69 6e 74 20 61
i n t m a i n ( i n t a
0000010 72 67 63 2c 20 63 68 61 72 2a 20 61 72 67 76 5b
r g c , c h a r * a r g v [
0000020 5d 20 29 20 7b 20 72 65 74 75 72 6e 20 37 3b 20
] ) { r e t u r n 7 ;
0000030 7d
}
0000031
------------------ output assembly ----------------------
1 .file "tzero.c"
2 .section ".text"
3 .align 4
4 .global main
5 .type main, #function
6 .proc 04
7 main:
8 save %sp, -176, %sp
9 mov %i0, %g1
10 stx %i1, [%fp+2183]
11 st %g1, [%fp+2175]
12 mov 7, %g1
13 sra %g1, 0, %g1
14 mov %g1, %i0
15 return %i7+8
16 nop
17 .size main, .-main
18 .ident "GCC: (genunix Fri Jan 2 11:56:03 GMT 2015) 4.9.2"
-----------------------------------------------------------
So there we see the lines 9 to 10 are for handling pointers to the
unused parameters. Makes no difference. The input should be rejected.
Dennis
