The x86-64 System V ABi doc may help. It’s a reference, albeit lightweight. The Variable Argument List reference starts on page 54, then it goes on, page 56-57 documents va_list: The va_list Type The va_list type is an array containing a single element of one structure containing the necessary information to implement the va_arg macro. … Read more
Since gcc-3.4.0, the ABI is forward compatible. I.E. a library made using an older release can be linked with a newer one and it should work (the reverse doesn’t). Obviously, there could be bugs, but there is only one mentionned in the documentation: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33678
A std::array<int, 3> is 96 bits wide on your implementation. As such the ABI declares that it should be returned in RAX + the low 32 bits of RDX (aka EDX). 4294967296 is 232, in hex it is $1’0000’0000. So the movabs stores 0 in the low order 32 bits of RAX, and 1 in … Read more
I would assume that it’s indicating packages compiled for little-endian and hard-float ABI as appropriate – i.e. it’s a software thing and only tangentially related to the hardware. In other words, you don’t actually have an “armv7l” processor – you have an ARMv7 processor which may well have a hardware FPU (and can run big-endian … Read more
Given these two quotes, is the red zone above the stacked return address or below the stacked return address? The red zone is the 128 bytes just below rsp, i.e. rsp – 128 to rsp – 1. Since this red zone is relative to RSP, does it move downward with each push and does it … Read more
From “Intel®64 and IA-32 Architectures Optimization Reference Manual”, section 4.4.2: “For best performance, the Streaming SIMD Extensions and Streaming SIMD Extensions 2 require their memory operands to be aligned to 16-byte boundaries. Unaligned data can cause significant performance penalties compared to aligned data.” From Appendix D: “It is important to ensure that the stack frame … Read more
Alignment helps the CPU fetch data from memory in an efficient manner: less cache miss/flush, less bus transactions etc. Some memory types (e.g. RDRAM, DRAM etc.) need to be accessed in a structured manner (aligned “words” and in “burst transactions” i.e. many words at one time) in order to yield efficient results. This is due … Read more
Bottom line: some technical limitations that amd64 has in using large addresses suggest dedicating the lower 2GiB of address space to code and data for efficiency. Thus the stack has been relocated out of this range. In i386 ABI1 stack is located before the code, growing from just under 0x8048000 downwards. Which provides “a little … Read more
You should not use libcxxabi directly. To my understanding it is a kind of platform abstraction library, providing low level functions needed to implement libcxx. If you are asking about using libcxx or libstdc++, the differences are mostly the license, newer standard version completeness (the clang project seems slightly faster in implementing recent C++ revisions) … Read more
The Shadow space (also sometimes called Spill space or Home space) is 32 bytes above the return address which the called function owns (and can use as scratch space), below stack args if any. The caller has to reserve space for their callee’s shadow space before running a call instruction. It is meant to be … Read more