https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94662
Bug ID: 94662
Summary: __attribute__ aligned is ignored
Product: gcc
Version: 9.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: petro.karashchenko at gmail dot com
Target Milestone: ---
__attribute__ 'aligned' is ignored.
Test case 1:
----------
int __attribute__((aligned(1))) var;
int foo(void)
{
return var;
}
----------
arm-none-eabi-gcc -save-temps -Wall -Wextra -c -mcpu=arm7tdmi -mthumb test.c
-O0
----------
Generated assembly:
.cpu arm7tdmi
.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, 6
.eabi_attribute 34, 0
.eabi_attribute 18, 4
.file "test.c"
.text
.comm var,4,1
.align 1
.global foo
.arch armv4t
.syntax unified
.code 16
.thumb_func
.fpu softvfp
.type foo, %function
foo:
@ Function supports interworking.
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 1, uses_anonymous_args = 0
push {r7, lr}
add r7, sp, #0
ldr r3, .L3
ldr r3, [r3]
movs r0, r3
mov sp, r7
@ sp needed
pop {r7}
pop {r1}
bx r1
.L4:
.align 2
.L3:
.word var
.size foo, .-foo
.ident "GCC: (GNU Tools for Arm Embedded Processors 9-2019-q4-major)
9.2.1 20191025 (release) [ARM/arm-9-branch revision 277599]"
----------
Test case 2:
----------
int __attribute__((aligned(1))) * var = (int *)0x03;
int foo(void)
{
return *var;
}
----------
arm-none-eabi-gcc -save-temps -Wall -Wextra -c -mcpu=arm7tdmi -mthumb test.c
-O0
----------
Generated assembly:
.cpu arm7tdmi
.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, 6
.eabi_attribute 34, 0
.eabi_attribute 18, 4
.file "test.c"
.text
.global var
.data
.type var, %object
.size var, 4
var:
.4byte 3
.text
.align 1
.global foo
.arch armv4t
.syntax unified
.code 16
.thumb_func
.fpu softvfp
.type foo, %function
foo:
@ Function supports interworking.
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 1, uses_anonymous_args = 0
push {r7, lr}
add r7, sp, #0
ldr r3, .L3
ldr r3, [r3]
ldr r3, [r3]
movs r0, r3
mov sp, r7
@ sp needed
pop {r7}
pop {r1}
bx r1
.L4:
.align 2
.L3:
.word var
.size foo, .-foo
.ident "GCC: (GNU Tools for Arm Embedded Processors 9-2019-q4-major)
9.2.1 20191025 (release) [ARM/arm-9-branch revision 277599]"
----------
Test case 3:
----------
int foo(void)
{
return *(int __attribute__((aligned(1))) *) 0x03;
}
----------
arm-none-eabi-gcc -save-temps -Wall -Wextra -c -mcpu=arm7tdmi -mthumb test.c
-O0
----------
Generated assembly:
.cpu arm7tdmi
.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, 6
.eabi_attribute 34, 0
.eabi_attribute 18, 4
.file "test.c"
.text
.align 1
.global foo
.arch armv4t
.syntax unified
.code 16
.thumb_func
.fpu softvfp
.type foo, %function
foo:
@ Function supports interworking.
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 1, uses_anonymous_args = 0
push {r7, lr}
add r7, sp, #0
movs r3, #3
ldr r3, [r3]
movs r0, r3
mov sp, r7
@ sp needed
pop {r7}
pop {r1}
bx r1
.size foo, .-foo
.ident "GCC: (GNU Tools for Arm Embedded Processors 9-2019-q4-major)
9.2.1 20191025 (release) [ARM/arm-9-branch revision 277599]"
----------
In all 3 test cases I'm expecting that unaligned access code should be
generated, but in all 3 test cases generated access is aligned.
However in next test case the align attribute actually takes effect:
----------
int foo(void)
{
return **(int * __attribute__((aligned(1))) *) 0x03;
}
int foo1(void)
{
return ***(int * __attribute__((aligned(1))) * __attribute__((aligned(1))) *)
0x03;
}
----------
arm-none-eabi-gcc -save-temps -Wall -Wextra -c -mcpu=arm7tdmi -mthumb test.c
-O0
----------
Generated assembly:
.cpu arm7tdmi
.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, 6
.eabi_attribute 34, 0
.eabi_attribute 18, 4
.file "test.c"
.text
.align 1
.global foo
.arch armv4t
.syntax unified
.code 16
.thumb_func
.fpu softvfp
.type foo, %function
foo:
@ Function supports interworking.
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 1, uses_anonymous_args = 0
push {r7, lr}
add r7, sp, #0
movs r3, #3
ldrb r2, [r3]
ldrb r1, [r3, #1]
lsls r1, r1, #8
orrs r2, r1
ldrb r1, [r3, #2]
lsls r1, r1, #16
orrs r2, r1
ldrb r3, [r3, #3]
lsls r3, r3, #24
orrs r3, r2
ldr r3, [r3]
movs r0, r3
mov sp, r7
@ sp needed
pop {r7}
pop {r1}
bx r1
.size foo, .-foo
.align 1
.global foo1
.syntax unified
.code 16
.thumb_func
.fpu softvfp
.type foo1, %function
foo1:
@ Function supports interworking.
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 1, uses_anonymous_args = 0
push {r7, lr}
add r7, sp, #0
movs r3, #3
ldrb r2, [r3]
ldrb r1, [r3, #1]
lsls r1, r1, #8
orrs r2, r1
ldrb r1, [r3, #2]
lsls r1, r1, #16
orrs r2, r1
ldrb r3, [r3, #3]
lsls r3, r3, #24
orrs r3, r2
ldrb r2, [r3]
ldrb r1, [r3, #1]
lsls r1, r1, #8
orrs r2, r1
ldrb r1, [r3, #2]
lsls r1, r1, #16
orrs r2, r1
ldrb r3, [r3, #3]
lsls r3, r3, #24
orrs r3, r2
ldr r3, [r3]
movs r0, r3
mov sp, r7
@ sp needed
pop {r7}
pop {r1}
bx r1
.size foo1, .-foo1
.ident "GCC: (GNU Tools for Arm Embedded Processors 9-2019-q4-major)
9.2.1 20191025 (release) [ARM/arm-9-branch revision 277599]"
----------
My expectation is next:
1. int __attribute__((aligned(1))) * var; -- aligned pointer to unaligned 'int'
value, hence the '*var' (memory addressed by pointer access) code should
generate a set of 'ldrb'->`lsls`->'orrs', but 'var' (pointer value access) code
should generate 'ldr'.
2. int * __attribute__((aligned(1))) var; -- unaligned pointer to aligned 'int'
value, hence the 'var' (pointer value access) code should generate a set of
'ldrb'->`lsls`->'orrs', but '*var' (memory addressed by pointer access) code
should generate 'ldr'.
3. int __attribute__((aligned(1))) * __attribute__((aligned(1))) var; --
unaligned pointer to unaligned 'int' value, hence both 'var' (pointer value
access) and '*var' (memory addressed by pointer access) code should generate a
set of 'ldrb'->`lsls`->'orrs'.
