Hello Leonid,
On 2024-02-07 18:15, Leonid Meyerovich wrote:
Using readelf helps, but I think there is some difference between
running readelf on the file and
parsing elf header in the memory (because my root process is already
in the memory)
As you can see below size of executable segment is different: readelf
=3923cb0, mycode=3923EB0
Also Entry point is different
This is unexpected, are you sure you are comparing the same binary?
Second segment starting address and size are the same (?)
I use __executable_start to parse ELF header in the memory
I don't think you can count on the ELF header being there though.
readelf -l Startup
Elf file type is EXEC (Executable file)
Entry point 0x40ef88
There are 4 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000400000
0x0000000000400000
0x0000000003923cb0 0x0000000003923cb0 RWE 0x1000
LOAD 0x0000000000000000 0x0000000003d30000
0x0000000003d30000
0x0000000000000000 0x0000000000aca428 RW 0x1000
TLS 0x00000000000cb490 0x00000000004cb490
0x00000000004cb490
0x0000000000000000 0x000000000000000c R 0x8
GNU_STACK 0x0000000000000000 0x0000000000000000
0x0000000000000000
0x0000000000000000 0x0000000000000000 RW 0x10
Section to Segment mapping:
Segment Sections...
00 .init .text .fini .rodata .eh_frame .init_array .fini_array
.got .got.plt .data ._archive_cpio __vsyscall _ps_irqchips
Anyway, writeable sections are put into segment 0 too, like .data,
so you can't just checksum the whole segment.
If you want to do these kind of things it's better to do with your
own linker script, then you have full control and can also let the
linker define section start and end symbols so you don't need to
parse ELF headers.
That said, the seL4 kernel has limitations, which is the reason
everything is put in the same segment for the startup task.
In your case just checksum between __executable_start and __etext,
which marks the end of the executable section.
(If you worry that your program is being modified, you can
just load your own program with proper memory protection
where you do everything and do as little as possible in
the startup task.)
Greetings,
Indan
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