FnAddr (Fnval n) emitted the symbol, which is right for a whole-program build
and wrong the instant anything is redefined into it. It now reads the cell,
and so does every direct call, which is what emit.ml's body_of does and is the
half that matters: a redefinition is one store, and it has to reach call sites
that already exist.
What is emitted, all of it behind dev:
- one cell per function in .data, .globl, initialised to the body this build
compiled. Spelled exactly as Emit.cellname spells it, because the point of
having one here is that an LLVM-built module binds
@"flan.cell.<n>" = external global ptr against it. nm -D over the two
builds of the same program gives identical sets of 68 cell symbols.
- the cell load placed after the arguments, which emit.ml has as a
load-bearing comment: a redefinition landing between two calls must not
land in the middle of one. CallPtr stays the other way round.
- the flan_dev_reg_enable constructor, which arms the allocation registry.
Not emitted: Emit.cellptr, the deeper spelling for a name the host was never
built with. It cannot arise in a whole-program build and belongs with the
redefinition module that would introduce one.
The --x86 --dev refusal is relaxed, and the argument is that flan dev never
reaches this fork: --x86 is read only by flan build, and the daemon builds
host and modules through Build.executable / Build.shared without it. So the
flag means a host whose call sites are redefinable, and nothing claims the
module that would redefine through them exists.
Two things were needed to believe any of that. First, the corpus with --dev on
both sides: 97 MATCH, 0 DIFFER, same as without it. Before the constructor was
added that read 96/1 — registry.flan asks (live? ...) and got four zeroes,
which is the whole of what a dev host does differently besides the cells.
Second, and the corpus cannot do this one: a dev build starts with every cell
pointing at the body this build compiled, so it prints what a release build
prints whether anything reads the cell or not. spike/x86/cells.sh preloads a
shared object whose constructor dlsyms flan.cell.twice and stores a different
body there -- the one store a redefinition ends in, done from outside, no
compiler involved. Both dev builds then print the new answer for a direct call
and for a function value, and both release builds are unchanged, which is what
says the change came from the indirection and not from symbol interposition.
One thing the later lane inherits, now written in both headers rather than
left to be discovered. x86.ml licenses its own calling convention on the
grounds that a dev build is compiled entirely here and a release build
entirely by LLVM, so the two never meet in one process. A cell an LLVM-built
module can store into is the first thing that could make that false: the
conventions agree on scalars and disagree on every aggregate, so an
Emit.redefinition module dlopened into an --x86 host would be right until the
first redefined function took or returned a struct. The answer is a
redefinition emitter here, not a classifier.
The transfer exit returned whatever the return temporary held where
emit.ml returns zero. Meaningless to a caller -- its guard sees the
channel set and never looks -- but main is a caller with no guard, and
what it finds in rax is the process exit status.
The survey compares stderr as well now, which is where every message
the new machinery produces goes: the bounds and slice errors, the
three restart refusals, the transfer failure. Each carries a location
this backend emits by hand as a .rodata label and a length in a
register, and an exit status of 134 with the wrong text beside it is
exactly the failure that reads as a match. It also walks spike/x86's
own probes.
p6-transfer.flan is the two re-propagation branches the corpus does
not reach. Every transfer in restarts.flan stops at a restart-case
inside the handler-bind's extent, so the handler frames never come off
on the transfer path; and in nested and shadowed the inner frame
offers the name, so a restart-case the transfer is not aimed at never
has to put the target back. allocators.flan already covers the third.
89 MATCH 0 DIFFER 0 refused, over test/programs and spike/x86,
comparing stdout, stderr and the exit status.
DISCUSS.md item 17 is the report.
The transfer channel was the only thing between 41 programs and the
corpus. It is there now: a guard after every Flan call, a landing pad
per restart-case, handler-bind and with-allocator, a transfer exit per
function that runs its fdefers, and check_at and check_slice, which
could not exist until the guard did.
Measured by what the programs print and what they exit with, never by
reading bytes. spike/x86/survey.sh builds every program in
test/programs both ways and diffs stdout and the exit status; it did
not exist, so it is here too, and it is the progress meter.
before 41 MATCH 1 DIFFER 41 refused by name
after 83 MATCH 0 DIFFER 0 refused by name
The one DIFFER was bounds.flan, and it was the honest answer to
"--x86 is silently a --no-bounds-checks build". It is not one any
more: check_at and check_slice signal through the channel exactly as
emit.ml's do, so a bounds violation signals, a restart-case catches
it, and an unhandled one exits 134 on both backends. The transitional
refusal that would have said so retired before it was written.
check_no_transfer is not removed, it is narrowed to the one place the
argument still holds: a global's initialiser runs from
flan..init-globals, before main and before anything can handle
anything, so a transfer out of it has nowhere to go.
Four bugs, and three of them are the shape item 16 predicted -- code
that reads correctly and answers wrong, found by output and not by
objdump:
- The body fell through into the transfer exit, so every fdefer ran
twice on a normal return. emit.ml cannot have this bug: its ret
terminates the block.
- A Vec crossed to the runtime as the address of a *copy*, so pushes
grew the copy and an in-bounds (at v 1) signalled against a length
of zero.
- ucomis sets CF, ZF and PF together for a NaN, so sete answered true
for (= x x) and the prelude's NaN test never fired: (/ 0.0 0.0)
formatted as -9223372036854775808. Flan's comparisons are LLVM's
ordered ones, so < and <= swap and =, != take a setnp beside them.
- A union read field 0 through the struct table and was refused by
name rather than laid out as a tag and a payload.
And one that could not have been found later: emit_globals_init stored
a null *into* the channel slot rather than a cell address into it,
which is a null pointer for every callee to write through. Harmless
while nothing could transfer; a fault the first time a guard loaded
through it.
