What directives should I use in GAS? I’ve found the ‘.org’ directive but GAS doesn’t seem to have a ‘.bits’ directive. The assembler defaults to 64–bit for me, you can use –32 or –64 to chose on the command line. Have a look at the manual for as to see how you can change the … Read more
By compiler: GCC: -Wa,-mbranches-within-32B-boundaries clang (10+): -mbranches-within-32B-boundaries compiler option directly, not -Wa. MSVC: /QIntel-jcc-erratum See Intel JCC Erratum – what is the effect of prefixes used for mitigation? ICC: TODO, look for docs. The GNU toolchain does mitigation in the assembler, with as -mbranches-within-32B-boundaries, which enables (GAS manual: x86 options): -malign-branch-boundary=32 (care about 32-byte boundaries). … Read more
With AT&T syntax you can put a label at the start of your bootloader and then use something like this: .global _start .text .code16 _start: jmp . .space 510-(.-_start) .word 0xaa55 Period . is the current location counter relative to the beginning of the current section. The difference between period . and _start is an … Read more
Excerpt from info as (GNU Binutils 2.21.90), or online in the GAS manual: https://sourceware.org/binutils/docs/as/Dot.html 5.4 The Special Dot Symbol The special symbol . refers to the current address that as is assembling into. Thus, the expression melvin: .long . defines melvin to contain its own address. Assigning a value to . is treated the same … Read more
To disable these, use the gcc option -fno-asynchronous-unwind-tables -fno-dwarf2-cfi-asm may be needed also.