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Also some highly non-obvious gotchas and notes, straight from the trenches: - VERY IMPORTANT: you'll be actually writing for a pre-ANSI C compiler! Anything yo

by akavel 12y ago

Also some highly non-obvious gotchas and notes, straight from the trenches: - VERY IMPORTANT: you'll be actually writing for a pre-ANSI C compiler! Anything you think you know about C may prove false! Example real-world discrepancy found when porting Lua (an extremely high-quality ANSI C codebase) to Go's cc: http://golang.org/issue/7027 http://golang.org/issue/7027 - The ternary operator (?:) is not supported on ARM (see: https://github.com/akavel/goluago/issues/8#issuecomment-41448868 https://github.com/akavel/goluago/issues/8#issuecomment-4144...) - You don't have #if, #elif - You must be super careful, and really know what you're doing, when trying to pass pointers through the C<->Go boundary, as you're entering GC (garbage collector)'s carefully tended house of cards - You don't have access to the C standard library (although, see https://github.com/akavel/gostdc https://github.com/akavel/gostdc) - Using varargs functions is non-trivial - You must ensure you include one special header in each and every C file (#include "runtime.h") because of special "extern register" variables; although, I'm not sure if this requirement was not removed in Go 1.3. Hm, that's all I could remember from the top of my head. If you have any questions, feel free to ask me by email (czapkofan@gmail.com) or, obviously, anyone on the golang-nuts mailing list. That said, it's sure fun! :D actually, maybe in part because of all that :)

4ad 12y ago
> you'll be actually writing for a pre-ANSI C compiler! I would not say the compiler is pre-ANSI. For example it even has some C99 features. Rather, it chose to ignore ANSI, so yes, you need to really careful with what your doing. The integer promotion rules are different, for example -1 < u16int(42) is false, unlike in ANSI C. > You must be super careful, and really know what you're doing, when trying to pass pointers through the C<->Go boundary Yes, however that is true with cgo as well. Especially now with the new precise garbage collector. > because of special "extern register" variables; although, I'm not sure if this requirement was not removed in Go 1.3. Nothing changed in 1.3, however big changes are coming into Go 1.4 and Go 1.5. Eventually all the C code in the runtime will go away. Until then, the plan is to move all remaining C code onto the scheduler stack instead of having common Go and C stacks, as that interferes with the copying stacks and the new precise garbage collector. In other words, using the Plan 9 C compiler in your project uses to work by accident. Not it appears as it would still work, but it actually has a subtle net negative effect that's not obvious to see at first glance. You should avoid it.

by akavel 12y ago

4ad 12y ago

> you'll be actually writing for a pre-ANSI C compiler! I would not say the compiler is pre-ANSI. For example it even has some C99 features. Rather, it chose to ignore ANSI, so yes, you need to really careful with what your doing. The integer promotion rules are different, for example -1 < u16int(42) is false, unlike in ANSI C. > You must be super careful, and really know what you're doing, when trying to pass pointers through the C<->Go boundary Yes, however that is true with cgo as well. Especially now with the new precise garbage collector. > because of special "extern register" variables; although, I'm not sure if this requirement was not removed in Go 1.3. Nothing changed in 1.3, however big changes are coming into Go 1.4 and Go 1.5. Eventually all the C code in the runtime will go away. Until then, the plan is to move all remaining C code onto the scheduler stack instead of having common Go and C stacks, as that interferes with the copying stacks and the new precise garbage collector. In other words, using the Plan 9 C compiler in your project uses to work by accident. Not it appears as it would still work, but it actually has a subtle net negative effect that's not obvious to see at first glance. You should avoid it.