* Remove the use of usrToCell in gcMark [backport:1.2]
Recently, we've discovered a GC crash resulting from inlining of
the memory allocation procs that allowed the compiler to avoid
maintaining any references to the "user pointer" on the stack.
Instead, a "cell pointer" appeared there and all field accesses
were performed with adjusted offsets. This interfered with the
ability of the GC to mark the correct cell in the conservative
stack scans which lead to premature collection of objects.
More details here:
af69b3ceae
This commit closes another theoretical loophole that may lead to
the same problem. If a short proc is accessing both the object and
its reference count in a short sequence of instructions, the compiler
may be enticed to reduce the number of registers being used by storing
only a single pointer to the object and using offsets when reading
and writing fields. A perfectly good strategy would be to store only
the cell pointer, so the reference count updates can be performed
without applying offsets. Accessing the fields of the object requires
offsets anyway, but these can be adjusted at compile-time without any
loss. Following this strategy will lead to the same problem of marking
a wrong cell during the conservative stack scan, leading to premature
collection.
The problem is avoided by not using `usrToCell` in `gcMark`. Since
the cell discovery logic can already handle interior pointers, the
user pointers don't need to be adjusted for the GC to function correctly.
* Allow use of colons inside fmt
allowing colons inside fmt by replacing the format specifier delimiter lets arbitrary nim code be run within fmt expressions.
Co-authored-by: flywind <xzsflywind@gmail.com>
* formatting,documentation,backslash escapes
Adding support for evaluating expressions by special-casing parentheses causes this regression: `&"""{ "(hello)" }"""` no longer parses.
In addition, code such as &"""{(if open: '(' else: ')')}""" wouldn't work.
To enable that, as well as the use of, e.g. Table constructors inside curlies, I've added backslash escapes.
This also means that if/for/etc statements, unparenthesized, will work, if the colons are escaped, but i've left that under-documented.
It's not exactly elegant having two types of escape, but I believe it's the least bad option.
* changelog
* added json strformat test
* pulled my thumb out and wrote a parser
Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
Co-authored-by: flywind <xzsflywind@gmail.com>
* fix failing test toSeq in manual which now works
* changelog
* reject proc fn(a: iterable)
* add iterable to spec
* remove MCS/UFCS limitation that now works
* Genode: move dyncall failures to runtime
Do not use the "error" pragma to warn that dynamic library loading is
not implemented, print a message at runtime and exit.
* Genode: use stricter dataspace type in page allocator
* Genode: remove compiler configuration from nim.cfg
Self-hosting Nim is not supported on Genode and defining the
cross-compilation environment can be done externally.
* Genode: use new mutex API
* Genode: call nim_component_construct as a C procedure
* Genode: implement echo for NimStringV2
* use sink and lent in deques
* Update lib/pure/collections/deques.nim
Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
* new `macros.genAst`: fixes all issues with `quote do`
* add changelog entry
* add workaround for https://github.com/nim-lang/Nim/issues/2465#issuecomment-511076669
* add test for #9607
* add kNoExposeLocalInjects option
* add test case for nested application of genAst
* genAst: automatically call newLit when needed
* allow skipping `{}`: genAst: foo
* add test that shows this fixes#11986
* add examples showing mixin; add examples showing passing types, macros, templates
* move to std/genasts
* improve docs
This is taken from:
af69b3ceae
Full original comment:
This is to avoid heavy inlining happening when two allocation calls
would occur shortly after each other.
This inlining would sometimes be accompanied with an optimisation
as the compiler is able to see that cellToUsr ending the first
allocation call is shortly followed by an usrToCell call. The
pointer arithmetic is redundant and the compiler can eliminate it,
leaving only the cell address in a register (and later the stack)
instead of the actual pointer to the user data, as one would expect.
This combined with a GC collect cycle will cause the stack scan to
only notice the cell address, which is of no good due to a usrToCell
in the gcMark call which shifts that address to an adjacent cell.
This means that the actual cell of importance will not get marked
and thus cause a premature collection of that cell. BOOM.
