c/2623: Wrong code when accessing unsigned short in a structure.

[niels dot beier at intel dot com]

>Number:         2623
>Category:       c
>Synopsis:       Wrong code when accessing unsigned short in a structure.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Tue Apr 24 03:36:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Niels Beier
>Release:        2.95.3 (20010315)
>Organization:
>Environment:
host: SunOs 5.6
target: arm-little-elf
Note: We are mixing arm and thumb code and we have therefore
added the thumb-interwork option to the library compilation:
TCFLGS = -fleading-underscore -mthumb-interwork
>Description:
Wrong code is generated when cross compiling the attached code for the arm architecture. An unsigned short (16 bit)  in a structure) is accessed as a 32 bit integer.  
>How-To-Repeat:
The following piece of C code generates wrong assembler code (accesses a unsigned short as an 32 bit integer).

2/proj/tools/arm/bin/arm-little-elf-gcc -O2 -g -Wall -c /2/proj/appl/router/ppp/45/test.c -o gal/test.o 
The following warnings are generated:
line 21: initialization makes pointer from integer without a cast
line 45: initialization makes pointer from integer without a cast

*****file: test.c ***********************************
typedef struct NBnotification_t {
    unsigned short 	code;
    unsigned short	prio;
    unsigned short	env;

    char	*txt;
    unsigned long	ssp;

    unsigned char	idlen;
    unsigned char 	*id;
    unsigned char	trap;
    unsigned char	varbind_switch;

    unsigned long	filter;
}  NBNOTIFICATION;


static NBNOTIFICATION NBNotifications[] =
{
{   1, 2, 3,
    4, 5,
    0, 0, 0, 0,
    6},
{   1,2,3,
    4, 0,
    12, 0, 13, 0,
    14 },

{   0, 0, 0,    0, 0,    0, 0, 0, 0,    0 }
};


NBNOTIFICATION *nbFindNotif(unsigned short code)
{
    NBNOTIFICATION *not = &NBNotifications[0];

    while (not->code != (unsigned short)0)
    {
    	if (code == not->code)
	    return(not);
        not++;
    }
    return(0);
}
*********************************
The resulting disassembled output is listed below:

gal/test.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <nbFindNotif>:
   0:   e1a0c00d        mov     r12, sp
   4:   e92dd800        stmdb   sp!, {r11, r12, lr, pc}
   8:   e24cb004        sub     r11, r12, #4    ; 0x4
   c:   e59f1038        ldr     r1, [pc, #38]   ; 4c <nbFindNotif+0x4c>
  10:   e1a00800        mov     r0, r0, lsl #16
  14:   e1d120b0        ldrh    r2, [r1]
  18:   e1a00840        mov     r0, r0, asr #16
  1c:   e3520000        cmp     r2, #0  ; 0x0
  20:   0a00000f        beq     64 <nbFindNotif+0x64>
  24:   e1a03800        mov     r3, r0, lsl #16
  28:   e1a00823        mov     r0, r3, lsr #16
  2c:   e1500002        cmp     r0, r2
  30:   01a00001        moveq   r0, r1
  34:   091ba800        ldmeqdb r11, {r11, sp, pc}
  38:   e5b12020        ldr     r2, [r1, #32]! /* Wrong: should be ldrh */
  3c:   e3520000        cmp     r2, #0  ; 0x0
  40:   1a000009        bne     6c <nbFindNotif+0x6c>
  44:   e3a00000        mov     r0, #0  ; 0x0
  48:   e91ba800        ldmdb   r11, {r11, sp, pc}
  4c:   00000000        andeq   r0, r0, r0

 
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: