ELF file .text section disappear after setting -Ttext with certain address

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I am trying to create a RISC-V based ZSBL.
The problem I’m having is that ELF .text section disappears as long as the address ends with 0, e.g. 0x300000, 0x3000100, etc. Why?

When the address is 0x2000000001, the output of readelf has .text section.

$riscv64-unknown-elf-as -c zsbl_cp_jmp.S -o zsbl_cp_jmp.o  
$riscv64-unknown-elf-ld -Ttext 0x2000000001  -nostdlib zsbl_cp_jmp.o -o zsbl_cp_jmp.elf

There are 7 section headers, starting at offset 0x11e8:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .text             PROGBITS        0000002000000001 001001 000003 00  AX  0   0  1
  [ 2] .init             PROGBITS        00000000000100b0 0000b0 00004c 00  AX  0   0  1
  [ 3] .riscv.attributes RISCV_ATTRIBUTES 0000000000000000 001004 00002e 00      0   0  1
  [ 4] .symtab           SYMTAB          0000000000000000 001038 000120 18      5   4  8
  [ 5] .strtab           STRTAB          0000000000000000 001158 000056 00      0   0  1
  [ 6] .shstrtab         STRTAB          0000000000000000 0011ae 000039 00      0   0  1

When the address is 0x2000000000, the.text section disappears.

$riscv64-unknown-elf-ld -Ttext 0x2000000000  -nostdlib zsbl_cp_jmp.o -o zsbl_cp_jmp.elf

There are 6 section headers, starting at offset 0x290:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .init             PROGBITS        0000000000010078 000078 00004c 00  AX  0   0  1
  [ 2] .riscv.attributes RISCV_ATTRIBUTES 0000000000000000 0000c4 00002e 00      0   0  1
  [ 3] .symtab           SYMTAB          0000000000000000 0000f8 000108 18      4   3  8
  [ 4] .strtab           STRTAB          0000000000000000 000200 000056 00      0   0  1
  [ 5] .shstrtab         STRTAB          0000000000000000 000256 000033 00      0   0  1

The source code is

.section .init

.global _start
_start:
    li      a0, 0x2000010000
    li      a1, 0x2000030000
    li      a2, 0x20000
    li      t0, 0
1:
    bge     t0, a2, 1f
    add     t1, a1, t0
    lb      t1, 0(t1)
    add     t2, a0, t0
    sb      t1, 0(t2)
    addi    t0, t0, 1
    j       1b
1:
    li t3, 0x2000010000
    jr t3

  • 2

    The assembly code you’re showing doesn’t have a .text section.

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  • It’s interesting that specifying an odd address makes a section appear in the linked binary that wasn’t present in the .o input. It has a size big enough to get to the next 4-byte alignment boundary, so probably the default linker script ends up emitting some padding. Like maybe the default linker script mentions .text enough that it has to get “optimized away” if empty.

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  • @ErikEidt In my understanding, if you set -Ttext, the .text section will appear. Is this understanding correct? If it’s not correct, how can we explain why .text section appears when the address is an odd number？e.g. 0x2000000001

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  • Maybe try putting a non-zero length .text section in the input and let us know what happens.

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  • [guessing] The padding required for the odd address is forcing a size of 3 bytes for the section which would otherwise be empty. With the even address, the empty section is eliminated. Perhaps this is what @PeterCordes already said.

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