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On Sun, 14 Sep 2025 22:42:46 -0700 >> Indu Bhagat wrote: >> >>> In such cases, the routines reading the SFrame data under consideration >>> here (SFrame FRE start addr, and SFrame FRE stack offsets) from memory >>> will need to use a memcpy to copy out the data to an aligned location. >>> >>> In GNU Binutils libsframe (used by ld), we do the above. Such a "SFrame >>> FRE decoding" routine could be provided in a arch-specific manner in >>> SFrame stack tracers. >> >> I'm perfectly fine with making it a requirement for the reader of the >> SFrame section having to use memcpy into an aligned structure for reading >> if the architecture requires it. Let only the architectures that have >> issues with unaligned access take the performance hit. >> >> -- Steve > > I agree. Unaligned access has nearly zero performance impact on modern > architectures, provided the access doesn't span additional cache > lines. > The padding required for alignment would increase the size, likely > creating more overhead than any alignment benefit would justify. > > ( > From a linker and binary utilities perspective, I'd even suggest > adopting a universal little-endian format regardless of the target > system's native endianness. > This would eliminate the need for endianness templates in the C++ code > and simplify toolchain implementation across platforms. > (Perhaps I am missing something) Wouldnt a toolchain implementation need endianness handling anyway to support cross toolchains? > On the big-endian z/Architecture, this is efficient: the LOAD REVERSED > instructions are used by the bswap versions in the following program, > not even requiring extra instructions. > #define WIDTH(x) \ > typedef __UINT##x##_TYPE__ [[gnu::aligned(1)]] uint##x; \ > uint##x load_inc##x(uint##x *p) { return *p+1; } \ > uint##x load_bswap_inc##x(uint##x *p) { return __builtin_bswap##x(*p)+1; }; \ > uint##x load_eq##x(uint##x *p) { return *p==3; } \ > uint##x load_bswap_eq##x(uint##x *p) { return __builtin_bswap##x(*p)==3; }; \ > > WIDTH(16); > WIDTH(32); > WIDTH(64); > ) For AArch64 which SFrame supports too, this is not true. AArch64 has both LE and BE.