Patching p -> scond = q -> scond in /sys/src/cmd/5l/noop.c fixes this
unfortunate linker bug.
On Sunday, April 28, 2013 10:54:18 PM UTC-7, Paul Patience wrote:
> Mischief reported a crash with on arm with
>
> winwatch when closing all windows excluding those
>
> ignored through the -e flag. Cinap_lenrek
>
> narrowed the problem down to a bug in the 5l
>
> linker: it generates incorrect code when using
>
> the conditional operator and dividing.
>
> A minimal test case is the following:
>
>
>
> term% cat foo.c
>
> #include <u.h>
>
> #include <libc.h>
>
>
>
> void
>
> main(void)
>
> {
>
> int i, j, k;
>
>
>
> i = 1;
>
> j = 0;
>
> k = j <= 0 ? 1 : 2/i;
>
> print("%d\n", k);
>
> exits(nil);
>
> }
>
>
>
> The output of asm(main) in acid is:
>
>
>
> acid: asm(main)
>
> main 0x00001020 MOVW.W R14,#-0x18(R13)
>
> main+0x4 0x00001024 MOVW $#0x1,R1
>
> main+0x8 0x00001028 MOVW $#0x0,R2
>
> main+0xc 0x0000102c CMP.S $#0x0,R2
>
> main+0x10 0x00001030 MOVW.LE R1,R3
>
> main+0x14 0x00001034 MOVW.GT $#0x2,R3
>
> main+0x18 0x00001038 SUB.GT $#0x8,R13,R13
>
> main+0x1c 0x0000103c MOVW R1,#0x4(R13)
>
> main+0x20 0x00001040 MOVW R3,R11
>
> main+0x24 0x00001044 BL _div
>
> main+0x28 0x00001048 MOVW R11,R3
>
> main+0x2c 0x0000104c ADD $#0x8,R13,R13
>
> main+0x30 0x00001050 MOVW $#0x7080,R0
>
> main+0x34 0x00001054 MOVW R3,#0x8(R13)
>
> main+0x38 0x00001058 BL print
>
> main+0x3c 0x0000105c MOVW $#0x0,R0
>
> main+0x40 0x00001060 BL exits
>
> main+0x44 0x00001064 RET.P #0x18(R13)
>
>
>
> The problem is that the division at main+0x24
>
> happens regardless of the comparison. The output
>
> from the compiler is correct, however:
>
>
>
> term% 5c -S foo.c
>
> TEXT main+0(SB),0,$20
>
> MOVW $1,R1
>
> MOVW $0,R2
>
> CMP $0,R2,
>
> MOVW.LE R1,R3
>
> MOVW.GT $2,R3
>
> DIV.GT R1,R3,R3
>
> MOVW $.string<>+0(SB),R0
>
> MOVW R3,8(R13)
>
> BL ,print+0(SB)
>
> MOVW $0,R0
>
> BL ,exits+0(SB)
>
> RET ,
>
> DATA .string<>+0(SB)/8,$"%d\n\z\z\z\z\z"
>
> GLOBL .string<>+0(SB),$8
>
> END ,
>
>
>
> A (temporary) workaround for this is using an
>
> if-else statement, for which the linker generates
>
> correct code.
>
>
>
> --
>
> pap
