What is the difference between the 386 and 32 bit options in ld -V?
elf32_x86_64elf_i386i386linuxi386pepi386pe
And, where can I find the documentation on these "emulation modes"
Add a comment |
1 Answer
The “emulation” selects different linker scripts; you’ll find the scripts themselves in /usr/lib/ldscripts on your system. The emulations you’ve listed correspond to
elf32_x86_64: ELF for x64-32, aka x32 — 32-bit x86-64 binarieself_i386: ELF for i386 — 32-bit i386 binariesi386linux: a.out for i386i386pep: PE+ for x86-64 — Windows-format 64-bit binariesi386pe: PE for i386 — Windows-format 32-bit binaries
The linker scripts define the output format and architecture, the search directories (where ld looks for libraries), the sections in the binary, among other things.
The linker script format is well documented (see above), but the available scripts aren’t; in most cases GCC will specify the right one, so you don’t need to worry about it, and in other cases you effectively end up needing to read the linker scripts themselves to figure out what they do.
- 1Extra info: x32 is a 32bit executable format, that will only run on x86_64. It is intended to use the benefits of x86 64bit mode, but be smaller than 64bit code. All data types (except time), are same as in 32bit mode.ctrl-alt-delor– ctrl-alt-delor2018-09-24 16:19:23 +00:00Commented Sep 24, 2018 at 16:19
-
- 1There's another format
elf_x86_64in theld -Voutput. I believe it is the same thing as theelf64-x86-64in theobjdump -iouput. Both should mean the 64-bit x86-64 binaries. Please correct me if I am wrong.smwikipedia– smwikipedia2019-11-01 04:24:56 +00:00Commented Nov 1, 2019 at 4:24 - Thanks for the
ldscripts/information, very useful! However it's not the end of the story. If/when you provide your own linker script like I did then ldscripts/ are ignored, you can move them out and everything still works. Yet even with all ldscripts/ gone (for testingld), I found there was still a difference between-melf_i386and-melf_x86_64! Alignment. The ELF output of the former was aligned to be mmapped on 4K pages and the latter on 2M pages. This was withld.bfd2.32.MarcH– MarcH2020-01-12 07:10:01 +00:00Commented Jan 12, 2020 at 7:10 - If you can't find
ldscripts/on your system, they're probably built in the executable. You can extract them like this:ld --verbose > default.xc,ld --verbose --melf_x86_64 --nmagic > elf_x86_64.xn, etc.MarcH– MarcH2020-01-13 01:28:16 +00:00Commented Jan 13, 2020 at 1:28