Re: [PATCH, ARM] Unaligned accesses for packed structures [1/2]

[Ye Joey]

Julian,

This patch works for register ld/st, but doesn't work for immediate,
as showed in example.

Would you further improve it for imm?

Thanks - Joey

$ arm-none-eabi-gcc -v 2>&1 | grep version
gcc version 4.7.0 20110922 (experimental) [trunk revision 179074] (GCC)
$ cat u.c
struct packed_str
{
        char f0;
        int  f1;
}__attribute__((packed)) u;

void foo(int a)
{
  u.f1 = a; // works fine
}

void bar()
{
  u.f1 = 1; // doesn't work
}

$ arm-none-eabi-gcc -mthumb -march=armv7 -S -O2 u.c
$ cat u.s
        .syntax unified
        .arch armv7
        .fpu softvfp
        .eabi_attribute 20, 1
        .eabi_attribute 21, 1
        .eabi_attribute 23, 3
        .eabi_attribute 24, 1
        .eabi_attribute 25, 1
        .eabi_attribute 26, 1
        .eabi_attribute 30, 2
        .eabi_attribute 34, 1
        .eabi_attribute 18, 4
        .thumb
        .file   "u.c"
        .text
        .align  2
        .global foo
        .thumb
        .thumb_func
        .type   foo, %function
foo:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        movw    r3, #:lower16:u
        movt    r3, #:upper16:u
        str     r0, [r3, #1]    @ unaligned
        bx      lr
        .size   foo, .-foo
        .align  2
        .global bar
        .thumb
        .thumb_func
        .type   bar, %function
bar:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        movw    r3, #:lower16:u
        movs    r1, #0
        movt    r3, #:upper16:u

@ Still uses aligned str from here
        ldrb    r2, [r3, #0]    @ zero_extendqisi2
        strb    r1, [r3, #4]
        orr     r2, r2, #256
        str     r2, [r3, #0]
        bx      lr
        .size   bar, .-bar
        .comm   u,5,4
        .ident  "GCC: (GNU) 4.7.0 20110922 (experimental) [trunk revision 
179074]"