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| -rw-r--r-- | lispref/internals.texi | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/lispref/internals.texi b/lispref/internals.texi index 8f15e308ad4..df9672b05b6 100644 --- a/lispref/internals.texi +++ b/lispref/internals.texi @@ -503,6 +503,18 @@ must declare these explicitly, with type @code{struct gcpro}. Thus, if you use @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. Alas, we can't explain all the tricky details here. + Remember that you must never initialise external variables (whether +static or not). If you do that, the linker will put the variable into +the initialised data area of the process, which on many architectures +becomes read-only when emacs is dumped (@pxref {Pure Storage}). + + Remember also that the keyword @code{static} is defined as nothing on +many architectures whose linkers would put every static variable in the +initialised data area, which becomes read-only after dumping. This +means that you must never use static local variables, because on those +architectures they would lose the @code{static} specifier and become +automatic. Use static external variables instead. + Defining the C function is not enough to make a Lisp primitive available; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. The code looks like |