* How to set alignment and READONLY of a brand new section
@ 2024-05-18 22:33 Massimiliano Cialdi
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From: Massimiliano Cialdi @ 2024-05-18 22:33 UTC (permalink / raw)
To: gcc-help
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Hi,
I apologize in advance if this is not the right place for this question.
In a software project of mine, on linux, I need to create a special section
that needs to be populated with 40 bytes large structures. Then I would
like to treat this section as an array.
For that I added this linker script with the -T option:
SECTIONS
{
/* section for CLI cmd array */
.CLI_cmd_section : ALIGN(8)
{
PROVIDE(__CLI_cmd_start = .);
KEEP(*(.CLI_cmd*));
. = ALIGN(8) ;
PROVIDE(__CLI_cmd_end = .);
}
}
INSERT AFTER .data;
Though, inspecting with objdump I see that the section is aligned to 32
bytes:
Sections:
Idx Name Size VMA LMA File
off Algn Flags
[...]
25 .data 00000008 0000000000009000 0000000000009000
00008000 2**3 CONTENTS, ALLOC, LOAD, DATA
26 .CLI_cmd_section 00000068 0000000000009020 0000000000009020
00008020 2**5 CONTENTS, ALLOC, LOAD, DATA
27 .bss 00000078 00000000000090a0 00000000000090a0
00008088 2**5 ALLOC
[...]
I thought it might be because some of the adjacent sections have such
alignment, but even moving it doesn't change
Sections:
Idx Name Size VMA LMA File
off Algn Flags
[...]
23 .dynamic 000001f0 0000000000008cf0 0000000000008cf0
00007cf0 2**3 CONTENTS, ALLOC, LOAD, DATA
24 .CLI_cmd_section 00000068 0000000000008ee0 0000000000008ee0
00007ee0 2**5 CONTENTS, ALLOC, LOAD, DATA
25 .got 000000a8 0000000000008f48 0000000000008f48
00007f48 2**3 CONTENTS, ALLOC, LOAD, DATA
26 .data 00000008 0000000000009000 0000000000009000
00008000 2**3 CONTENTS, ALLOC, LOAD, DATA
[...]
I wanted to try to see what happened to impose a higher alignment (64) and
in this case it sets it. So it seems that for some reason right now I can't
get below 32 on that section.
this is very annoying, because in the array the compiler considers the
entries offset by 40 bytes, while the linker has them offset by 64 bytes.
How should I get my array indexed well, and then impose alignment 8?
Also I would like this section to be READONLY, but if I try to impose it I
get a warning on the link which I don't know how "serious" it is:
/usr/bin/ld: /tmp/ccDmg9Dd.o: warning: relocation in read-only section
`.CLI_cmd.__CLI_cmd_help'
/usr/bin/ld: warning: creating DT_TEXTREL in a PIE
Is there a safe, reliable and "clean" way to impose READONLY the
.CLI_cmd_section without having errors/warning from the linker?
best regard
Max
--
Et nunc, auxilium solis, vincam!
Oppugnatio solaris!
VIS!
Massimiliano Cialdi
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