[LLVMdev] ARM assembler's syntax in clang

[Bernie Ogden]

Not sure, but I would try:

 

1. Are the objects being linked in the right order?

2. Is the symbol name _data_table correct?

3. You may need to explicitly tell your use_table.s file about the existence of data_table. In armasm I would have an 'import' statement to achieve this, not sure about clang/gas.

 

You also need to return from foo _before_ you execute '.long _data_table'. And be warned that the PC doesn't point at the next instruction when you use it like this - I believe you don't need to modify it at all if you swap the pop and the .long.

 

From: Ashi [mailto:ashi08104 at gmail.com] 
Sent: 07 March 2013 11:39
To: Bernard Ogden
Cc: Renato Golin; LLVM List
Subject: Re: [LLVMdev] ARM assembler's syntax in clang

 

Hi, Bernie, Thanks for your reply!
However, I still have problem by following edk2's code, my test code is attached, what I want to do is build it as a dynamic lib. But I get error from ld:
ld: illegal text-relocation to _data_table in table.o from foo in use_table.o for architecture armv7

Do you have any suggestion to solve this? Thanks!

//==begin table.c==
int data_table[] = {0xff, 0xff};
//==end table.c==

//==begin use_table.s ==
        .text
        .syntax unified
        .align   4
        .global   foo
        .thumb
        .thumb_func

foo:
        PUSH {lr}
        @LDR         r0,[PC,#2]
        .long _data_table
        POP {pc}
//==end use_table.s==

//==begin Makefile==
CC = /Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
CFLAG = -arch armv7 -mcpu=cortex-a9 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPh
oneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk 

all:libtest.dylib 

libtest.dylib:table.o use_table.o
        $(CC) -v  -dynamiclib $(CFLAG) $^ -o $@
table.o:table.c
        $(CC) -c $(CFLAG) $^ -o $@
use_table.o:use_table.s
        $(CC) -c -integrated-as $(CFLAG) $^ -o $@
clean:
        rm *.o libtest.dylib test
//==end Makefile==


Cheers,
Ashi

 

On Wed, Mar 6, 2013 at 11:59 PM, Bernie Ogden <bogden at arm.com> wrote:

Hi Ashi,

 

Your first LDR is a pseudoinstruction that is supported by some tools (gas and armasm, at least), but not by LLVM. Roughly speaking, it turns into a PC-relative load from a literal pool.

 

To do what you're trying to achieve you can write your own literal pool in your assembly. You can see some examples of this sort of thing at https://github.com/tianocore/edk2/blob/master/ArmPkg/Include/AsmMacroIoLib.h.

 

Regards,

 

Bernie

 

 

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Ashi
Sent: 05 March 2013 04:27
To: Renato Golin
Cc: LLVM List
Subject: Re: [LLVMdev] ARM assembler's syntax in clang

 

Hi, all. The previous post have a typo:

problem in ARM assembly: I use LDR to load an external symbol :

LDR         R7,=DataTable

But clang gives error: unexpected token in operand to the '=', 
Then I change the code to:

LDR         R7,DataTable

The error becomes: unsupported relocation on symbol. How can I get around this in clang? My problem is actually how to load external symbol in Clang's integrated-as? I've tried to learn some trivial c code's assembly output, but find there are many linker related symbol and really confusing.

Thanks in advance!

 

On Mon, Mar 4, 2013 at 4:48 PM, Ashi <ashi08104 at gmail.com> wrote:

Hi, all. Another problem in ARM assembly: I use LDR to load an external symbol :

LDR         R7,=DataTable

But clang gives error: unexpected token in operand to the '=', 
Then I change the code to:

LDR         R7,=DataTable

The error becomes: unsupported relocation on symbol. How can I get around this in clang? 

Thanks in advance!

 

On Mon, Feb 25, 2013 at 7:14 PM, Ashi <ashi08104 at gmail.com> wrote:

Hi,all,
I've some problem when using clang compile my ARM assembly code:

1 .qn directive
In GAS, .qn directive is used to create typed and/or indexed register aliases for use in Advanced SIMD Extension (Neon) instructions.(http://sourceware.org/binutils/docs/as/ARM-Directives.html#ARM-Directives)
But clang's integrated-as seems have different syntax, for example, my code:

input .qn Q6.F32 

Clang would give error: unexpected token in argument list

2 .unreq
Clang doesn't recognize .unreq,  my code is as below:

px .req r0
.unreq px
px .req r1

clang give error: redefinition of 'px' does not match original.

3 .end
clang also doesn't recognize .end directive

all my code is compiled by: clang -arch armv7 -v -integrated-as -g -mcpu=cortex-a9 -mfpu=neon -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk/

my clang version is: Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)

BTW, could any tell me which files implement integrated-as in clang source code, I think it may also help me by looking the source code(I've tried 'grep', but with no success.)

Great Thanks!

ashi

ashi

 

 
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