Combining two assembly files together with both text and data section

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I have two assembly files, a.s and b.s I want to combine both of them and create a new assembly file c.s The file c.s should have all the code in .text of a.s and then all then code in .text of b.s I want to do the same thing with .data section

# File a.s
VSUB.F32 S4, S5, S6
.data
.word 0x10000000

# File b.s
VADD.F32 S4, S5, S6
.data
.word 0x20000000

# File c.s
.include "a.s"
.include "b.s"

I want my output to look like this:

.text
VSUB.F32 S4, S5, S6
VADD.F32 S4, S5, S6

.data
.word 0x10000000
.word 0x20000000

However, this is what I see after dumping the object file.

Disassembly of section .text:

00000000 <.text>:
0:  ee322ac3    vsub.f32    s4, s5, s6


00000000 <.data>:
0:  10000000    .word   0x10000000
4:  ee710a21    vadd.f32    s1, s2, s3
8:  20000000    .word   0x20000000
gcc
assembly
arm
asked on Stack Overflow Feb 8, 2019 by Amardeep reddy • edited Feb 8, 2019 by Amardeep reddy

2 Answers

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thats exactly what a linker does what is the problem?

a.s

add r0,r0,r0

.data

aaa: .word 0xAAAAAAAA

b.s

add r1,r1,r1

.data

bbbb: .word 0xBBBBBBBB

build:

arm-none-eabi-as a.s -o a.o
arm-none-eabi-as b.s -o b.o
arm-none-eabi-ld -Ttext=0x1000 -Tdata=0x2000 a.o b.o -o ab.elf
arm-none-eabi-ld: warning: cannot find entry symbol _start; defaulting to 0000000000001000

disassemble:

arm-none-eabi-objdump -D ab.elf

Disassembly of section .text:

00001000 <.text>:
    1000:   e0800000    add r0, r0, r0
    1004:   e0811001    add r1, r1, r1

Disassembly of section .data:

00002000 <__data_start>:
    2000:   aaaaaaaa    bge feaacab0 <_stack+0xfea2cab0>

00002004 <bbbb>:
    2004:   bbbbbbbb    bllt    feef0ef8 <_stack+0xfee70ef8>

completely useless code but its that simple. You can then complicate it more by using a linker script, etc.

Naturally the code needs to make sense it wants to branch or call functions locally or in other objects with a sane flow. But it is easy to see with this example that the linker simply put the .text sections together and the .data sections together.

Unless dictated by a linker script the order they land in the output so far as I have seen is determined by the order found on the linker command line.

answered on Stack Overflow Feb 8, 2019 by old_timer • edited Feb 8, 2019 by old_timer
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Add .text to the beginning of each file.

The assembler starts with the section set to .text. However, when you use .include, it is in the context of the including file (c.s in your case) which has the section set to .data from the previous include.

Theoretically, you only have to add a .text to the top of the b.s source, but it is always good practice to just always use a .text declaration at the start of your asembler file. You might like .unified, .thumb, etc.

It is true that a linker will solve this issue, but a common practical case is mixing generated assembler with custom code. Generally, you just need driver.s to include generated.s and don't need the third file. The generated file is typical a table or data structure from another source such as 'C' structure offsets, conversion constants, etc.

answered on Stack Overflow Feb 8, 2019 by prl • edited Feb 8, 2019 by artless noise

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