Re: [uClinux-dev] [PATCH] Valid relocation symbol for FLAT formaton ARM, v2

From: Jun Sun
Date: Mon Jan 04 2010 - 13:58:48 EST

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In reply to: Jamie Lokier: "Re: [uClinux-dev] [PATCH] Valid relocation symbol for FLAT format on ARM, v2"
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On Sat, Jan 02, 2010 at 11:09:07PM +0000, Jamie Lokier wrote:
> Jun Sun wrote:
> > +/* [jsun] new gcc 4.x generates ANCHOR symbols in order to reduce the size
> > + * of GOT table for PIC code. It is possible the ANCHOR is placed beyond
> > + * the end of data/bss segment up to 4K bytes(12 bits), because ARM allows
> > + * negative 12-bit offset. Thus we allow 0x1000 extra in reloc address range.
> > + */
>
> Can you provide a small test program and *exact* GCC version and
> Binutils version which triggers this? People have reported using GCC
> 4.x on ARM uClinux for some time, and I haven't seen complaints
> about this problem before.
>

gcc is derived from code saucery's 2008Q2 release, I believe. It is
gcc 4.3.3. So there is minor chance that this ANCHOR feature
is a code sourcery feature rather than a generic gcc 4.3.3. Please help
verify.

I attached the sample code and the assembly output. The command line used
to generate this is:

arm-uclinuxeabi-gcc -c -Os -g -fomit-frame-pointer -pipe -msoft-float -fno-common -fno-builtin -Wall -DEMBED -D__PIC__ -fpic -msingle-pic-base -Dlinux -D__linux__ -Dunix -D__uClinux__ -S helloworld.c

You can see from the assembly output that .LANCHOR1 is set to 8184, well
beyond the real end of bss/data segment. And it is easy to see why, because
variable x2 is then referred as a negative offset to LANCHOR1.

Cheers.

Jun
#include <stdio.h>

char msg[]="hello, world";

static char buf[4092];
static int x1;
static int x2;

int main()
{
buf[0]=0;
x1 = 5;
x2 = 6;
printf("%s\n", msg);
printf("main() is @ %08x\n", &main);
printf("buf = 0x%x, x1 @ 0x%x, x2 @ 0x%x\n", buf, &x1, &x2);
return 0;
}
.cpu arm7tdmi
.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, 2
.eabi_attribute 30, 4
.eabi_attribute 18, 4
.file "helloworld.c"
.section .debug_abbrev,"",%progbits
.Ldebug_abbrev0:
.section .debug_info,"",%progbits
.Ldebug_info0:
.section .debug_line,"",%progbits
.Ldebug_line0:
.text
.Ltext0:
.align 2
.global main
.type main, %function
main:
.LFB2:
.file 1 "helloworld.c"
.loc 1 10 0
@ Function supports interworking.
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
.loc 1 11 0
ldr r3, .L3
.loc 1 10 0
stmfd sp!, {r4, r5, r6, lr}
.LCFI0:
.loc 1 11 0
ldr r4, [r9, r3]
.loc 1 13 0
ldr r3, .L3+4
ldr r5, [r9, r3]
.loc 1 14 0
ldr r3, .L3+8
ldr r1, [r9, r3]
ldr r3, .L3+12
ldr r0, [r9, r3]
.loc 1 12 0
mov r3, #5
.loc 1 11 0
mov r6, #0
.loc 1 12 0
str r3, [r4, #4092]
.loc 1 13 0
add r3, r3, #1
str r3, [r5, #-4088]
.loc 1 11 0
strb r6, [r4, #0]
.loc 1 14 0
bl printf
.loc 1 15 0
ldr r3, .L3+16
ldr r0, [r9, r3]
ldr r3, .L3+20
ldr r1, [r9, r3]
bl printf
.loc 1 16 0
ldr r0, .L3+24
sub r3, r5, #4080
add r2, r4, #4080
mov r1, r4
ldr r0, [r9, r0]
add r2, r2, #12
sub r3, r3, #8
bl printf
.loc 1 18 0
mov r0, r6
ldmfd sp!, {r4, r5, r6, lr}
bx lr
.L4:
.align 2
.L3:
.word .LANCHOR0(GOT)
.word .LANCHOR1(GOT)
.word msg(GOT)
.word .LC0(GOT)
.word .LC1(GOT)
.word main(GOT)
.word .LC2(GOT)
.LFE2:
.size main, .-main
.global msg
.section .rodata.str1.1,"aMS",%progbits,1
.LC0:
.ascii "%s\012\000"
.LC1:
.ascii "main() is @ %08x\012\000"
.LC2:
.ascii "buf = 0x%x, x1 @ 0x%x, x2 @ 0x%x\012\000"
.data
.type msg, %object
.size msg, 13
msg:
.ascii "hello, world\000"
.bss
.align 2
.set .LANCHOR0,. + 0
.set .LANCHOR1,. + 8184
.type buf, %object
.size buf, 4092
buf:
.space 4092
.type x1, %object
.size x1, 4
x1:
.space 4
.type x2, %object
.size x2, 4
x2:
.space 4
.section .debug_frame,"",%progbits
.Lframe0:
.4byte .LECIE0-.LSCIE0
.LSCIE0:
.4byte 0xffffffff
.byte 0x1
.ascii "\000"
.uleb128 0x1
.sleb128 -4
.byte 0xe
.byte 0xc
.uleb128 0xd
.uleb128 0x0
.align 2
.LECIE0:
.LSFDE0:
.4byte .LEFDE0-.LASFDE0
.LASFDE0:
.4byte .Lframe0
.4byte .LFB2
.4byte .LFE2-.LFB2
.byte 0x4
.4byte .LCFI0-.LFB2
.byte 0xe
.uleb128 0x10
.byte 0x8e
.uleb128 0x1
.byte 0x86
.uleb128 0x2
.byte 0x85
.uleb128 0x3
.byte 0x84
.uleb128 0x4
.align 2
.LEFDE0:
.text
.Letext0:
.section .debug_loc,"",%progbits
.Ldebug_loc0:
.LLST0:
.4byte .LFB2-.Ltext0
.4byte .LCFI0-.Ltext0
.2byte 0x1
.byte 0x5d
.4byte .LCFI0-.Ltext0
.4byte .LFE2-.Ltext0
.2byte 0x2
.byte 0x7d
.sleb128 16
.4byte 0x0
.4byte 0x0
.section .debug_info
.4byte 0xee
.2byte 0x2
.4byte .Ldebug_abbrev0
.byte 0x4
.uleb128 0x1
.4byte .LASF10
.byte 0x1
.4byte .LASF11
.4byte .LASF12
.4byte .Ltext0
.4byte .Letext0
.4byte .Ldebug_line0
.uleb128 0x2
.byte 0x4
.byte 0x7
.4byte .LASF0
.uleb128 0x2
.byte 0x2
.byte 0x7
.4byte .LASF1
.uleb128 0x2
.byte 0x4
.byte 0x7
.4byte .LASF2
.uleb128 0x2
.byte 0x4
.byte 0x5
.4byte .LASF3
.uleb128 0x3
.byte 0x4
.byte 0x5
.ascii "int\000"
.uleb128 0x2
.byte 0x1
.byte 0x8
.4byte .LASF4
.uleb128 0x2
.byte 0x8
.byte 0x5
.4byte .LASF5
.uleb128 0x4
.byte 0x4
.byte 0x7
.uleb128 0x2
.byte 0x1
.byte 0x8
.4byte .LASF6
.uleb128 0x2
.byte 0x1
.byte 0x6
.4byte .LASF7
.uleb128 0x2
.byte 0x2
.byte 0x5
.4byte .LASF8
.uleb128 0x2
.byte 0x8
.byte 0x7
.4byte .LASF9
.uleb128 0x5
.byte 0x1
.4byte .LASF13
.byte 0x1
.byte 0xa
.4byte 0x41
.4byte .LFB2
.4byte .LFE2
.4byte .LLST0
.uleb128 0x6
.4byte 0x48
.4byte 0x9e
.uleb128 0x7
.4byte 0x56
.2byte 0xffb
.byte 0x0
.uleb128 0x8
.ascii "buf\000"
.byte 0x1
.byte 0x5
.4byte 0x8d
.byte 0x5
.byte 0x3
.4byte buf
.uleb128 0x8
.ascii "x1\000"
.byte 0x1
.byte 0x6
.4byte 0x41
.byte 0x5
.byte 0x3
.4byte x1
.uleb128 0x8
.ascii "x2\000"
.byte 0x1
.byte 0x7
.4byte 0x41
.byte 0x5
.byte 0x3
.4byte x2
.uleb128 0x6
.4byte 0x48
.4byte 0xdf
.uleb128 0x9
.4byte 0x56
.byte 0xc
.byte 0x0
.uleb128 0xa
.ascii "msg\000"
.byte 0x1
.byte 0x3
.4byte 0xcf
.byte 0x1
.byte 0x5
.byte 0x3
.4byte msg
.byte 0x0
.section .debug_abbrev
.uleb128 0x1
.uleb128 0x11
.byte 0x1
.uleb128 0x25
.uleb128 0xe
.uleb128 0x13
.uleb128 0xb
.uleb128 0x3
.uleb128 0xe
.uleb128 0x1b
.uleb128 0xe
.uleb128 0x11
.uleb128 0x1
.uleb128 0x12
.uleb128 0x1
.uleb128 0x10
.uleb128 0x6
.byte 0x0
.byte 0x0
.uleb128 0x2
.uleb128 0x24
.byte 0x0
.uleb128 0xb
.uleb128 0xb
.uleb128 0x3e
.uleb128 0xb
.uleb128 0x3
.uleb128 0xe
.byte 0x0
.byte 0x0
.uleb128 0x3
.uleb128 0x24
.byte 0x0
.uleb128 0xb
.uleb128 0xb
.uleb128 0x3e
.uleb128 0xb
.uleb128 0x3
.uleb128 0x8
.byte 0x0
.byte 0x0
.uleb128 0x4
.uleb128 0x24
.byte 0x0
.uleb128 0xb
.uleb128 0xb
.uleb128 0x3e
.uleb128 0xb
.byte 0x0
.byte 0x0
.uleb128 0x5
.uleb128 0x2e
.byte 0x0
.uleb128 0x3f
.uleb128 0xc
.uleb128 0x3
.uleb128 0xe
.uleb128 0x3a
.uleb128 0xb
.uleb128 0x3b
.uleb128 0xb
.uleb128 0x49
.uleb128 0x13
.uleb128 0x11
.uleb128 0x1
.uleb128 0x12
.uleb128 0x1
.uleb128 0x40
.uleb128 0x6
.byte 0x0
.byte 0x0
.uleb128 0x6
.uleb128 0x1
.byte 0x1
.uleb128 0x49
.uleb128 0x13
.uleb128 0x1
.uleb128 0x13
.byte 0x0
.byte 0x0
.uleb128 0x7
.uleb128 0x21
.byte 0x0
.uleb128 0x49
.uleb128 0x13
.uleb128 0x2f
.uleb128 0x5
.byte 0x0
.byte 0x0
.uleb128 0x8
.uleb128 0x34
.byte 0x0
.uleb128 0x3
.uleb128 0x8
.uleb128 0x3a
.uleb128 0xb
.uleb128 0x3b
.uleb128 0xb
.uleb128 0x49
.uleb128 0x13
.uleb128 0x2
.uleb128 0xa
.byte 0x0
.byte 0x0
.uleb128 0x9
.uleb128 0x21
.byte 0x0
.uleb128 0x49
.uleb128 0x13
.uleb128 0x2f
.uleb128 0xb
.byte 0x0
.byte 0x0
.uleb128 0xa
.uleb128 0x34
.byte 0x0
.uleb128 0x3
.uleb128 0x8
.uleb128 0x3a
.uleb128 0xb
.uleb128 0x3b
.uleb128 0xb
.uleb128 0x49
.uleb128 0x13
.uleb128 0x3f
.uleb128 0xc
.uleb128 0x2
.uleb128 0xa
.byte 0x0
.byte 0x0
.byte 0x0
.section .debug_pubnames,"",%progbits
.4byte 0x1f
.2byte 0x2
.4byte .Ldebug_info0
.4byte 0xf2
.4byte 0x75
.ascii "main\000"
.4byte 0xdf
.ascii "msg\000"
.4byte 0x0
.section .debug_aranges,"",%progbits
.4byte 0x1c
.2byte 0x2
.4byte .Ldebug_info0
.byte 0x4
.byte 0x0
.2byte 0x0
.2byte 0x0
.4byte .Ltext0
.4byte .Letext0-.Ltext0
.4byte 0x0
.4byte 0x0
.section .debug_str,"MS",%progbits,1
.LASF5:
.ascii "long long int\000"
.LASF0:
.ascii "unsigned int\000"
.LASF11:
.ascii "helloworld.c\000"
.LASF13:
.ascii "main\000"
.LASF2:
.ascii "long unsigned int\000"
.LASF9:
.ascii "long long unsigned int\000"
.LASF6:
.ascii "unsigned char\000"
.LASF4:
.ascii "char\000"
.LASF12:
.ascii "/home/jsun/work/lincos/trunk/add_on/helloworld_c\000"
.LASF3:
.ascii "long int\000"
.LASF8:
.ascii "short int\000"
.LASF1:
.ascii "short unsigned int\000"
.LASF7:
.ascii "signed char\000"
.LASF10:
.ascii "GNU C 4.3.3\000"
.ident "GCC: (Netspectrum uClinux EABI) 4.3.3"

Next message: H. Peter Anvin: "Re: Subject: [PATCH 1/2] x86: get back 15 vectors"
Previous message: Dmitry Torokhov: "Re: drm_vm.c:drm_mmap: possible circular locking dependency detected"
In reply to: Jamie Lokier: "Re: [uClinux-dev] [PATCH] Valid relocation symbol for FLAT format on ARM, v2"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]