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"ELF-Symbols" tag for relocatable images
From: |
Ahmed, Safayet (GE Global Research, US) |
Subject: |
"ELF-Symbols" tag for relocatable images |
Date: |
Fri, 17 Mar 2017 19:53:51 +0000 |
Hello again,
I had a question on the function, "grub_multiboot_load_elf(32/64)".
(grub/grub_core/loader/multiboot_elfxx.c: line 54)
As a part of parsing an ELF image, the above-named function copies the section
header table into memory, and copies "unloaded" sections into memory (lines 199
- 269). The section table may be passed to an OS image as the "ELF-Symbols" tag
of the multiboot2 information structure.
Section 2.6.7 of the specification states that "the physical address fields of
the ELF section header then refer to where the sections are in memory".
Sections that are loaded are handled differently in the code from sections that
are not loaded. This distinction is made at line 234. The loaded sections are
ignored.
The "sh_addr" field of entries in the table for not-loaded sections are
explicitly updated to point to the address where those sections are copied
(line 265).
For "loaded" sections loaded to a fixed address, the "sh_addr" field of the
section header table entries should be accurate without any updates. However,
if the image is relocated, the "sh_addr" field of the entries for relocated
sections are not necessarily accurate.
Is this a legitimate concern? Alternatively, should the section header table be
absent from ELF images that contain the "relocatable tag" in the multiboot2
header? Under normal circumstances, the section header table isn't really
necessary for loading.
thank you,
Safayet N Ahmed Ph.D
Researcher, Computer Engineer
GE Global Research Center
One Research Circle,
Niskayuna, NY 12309 United States
General Electric Company, GE Global Research
GE imagination at work
- "ELF-Symbols" tag for relocatable images,
Ahmed, Safayet (GE Global Research, US) <=
- Re: "ELF-Symbols" tag for relocatable images, Andrei Borzenkov, 2017/03/19
- Re: "ELF-Symbols" tag for relocatable images, Daniel Kiper, 2017/03/22
- Re: "ELF-Symbols" tag for relocatable images, Andrei Borzenkov, 2017/03/22
- Re: "ELF-Symbols" tag for relocatable images, Daniel Kiper, 2017/03/22
- Re: "ELF-Symbols" tag for relocatable images, Rodrigo Valiña Gutiérrez, 2017/03/22
- Re: "ELF-Symbols" tag for relocatable images, Daniel Kiper, 2017/03/22
- Re: "ELF-Symbols" tag for relocatable images, Andrei Borzenkov, 2017/03/23
- Re: "ELF-Symbols" tag for relocatable images, Rodrigo V. G., 2017/03/23
- Re: "ELF-Symbols" tag for relocatable images, Andrei Borzenkov, 2017/03/26
- Re: "ELF-Symbols" tag for relocatable images, Andrei Borzenkov, 2017/03/23