https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=216316
--- Comment #9 from Michael Brown <mc...@ipxe.org> ---
(In reply to Ed Maste from comment #8)
Thanks for taking a look. The multiple sections all with virtual memory
addresses of zero are correct: there are genuinely multiple disjoint address
spaces at runtime. For example: the real-mode code segment (.text16) and
real-mode data segment (.data16) may be placed arbitrarily in base memory once
loaded, and virtual addresses within those segments are just 16-bit offsets
from the start of each segment, dereferenced against %cs or %ds as applicable.
The load memory addresses (LMA) that we create within the ELF file represent
the offsets at which we expect each section to appear in the file generated by
"objcopy -O binary".
Looking at the output of "objdump -h bin/ipxe.dsk.tmp" I see e.g.:
objdump -h bin/ipxe.dsk.tmp
bin/ipxe.dsk.tmp: file format elf32-i386-freebsd
Sections:
Idx Name Size VMA LMA File off Algn
0 .prefix 0000090d 00000000 00000000 00000154 2**0
CONTENTS, ALLOC, LOAD, CODE
...
7 .textdata 000ce040 00000000 00001370 000014c0 2**5
CONTENTS, ALLOC, LOAD, CODE
which correctly shows that we have (at least) two sections with a VMA of
00000000, but that .prefix should appear at offset 00000000 and .textdata at
offset 00001370 within the "-O binary" output file based on the LMA of each
section.
The binutils objcopy does behave this way: it will use the load memory
addresses as the file offsets for "-O binary" (with the first byte in the
output file corresponding to the lowest load memory address present in the
output).
The binutils objcopy behaviour seems correct to me: since "-O binary" is
intended to create a raw binary image then the LMA (rather than the VMA) is the
relevant value for the offset within this binary image.
Could the elftoolchain objcopy be made to match this behaviour?
Thanks,
Michael
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