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Malte Ubl
994a6b9940
The tree-shaking test failed on Linux x64 with "expected 68344 to be less
than 65536". Measured with the release helper/runtime-pack pipeline in a
Linux x64 sandbox (hello = console.log("hello", "world")):
PR file .text R+E segment
#743 64256 15794 0x3f11
#744 68416 16050 0x4011
#764 68520 16546 0x4221
The allocator adds 256 bytes of .text to hello: the inline scr_mem_free
fast path in the release functions hello already links (scr_str_release,
scr_arr_destroy, scr_arr_gc_free, scr_cyc_free, scr_dyn_dispose). Its
slow path and address-space reservation (scr_sa_slow, scr_sa_reserve)
are already stripped from hello. ELF segments are page aligned, and #743
left only 239 bytes before the executable segment's 16 KiB page, so 17
bytes over the boundary move every later segment, and the file, by 4 KiB.
Shrinking hello back under the old ceiling is not a reasonable trade.
At the top of the stack the executable segment is 545 bytes past the
page boundary. The extra bytes come from hot-path code the later PRs add
on purpose (number-to-string fast paths in scr_f64_to_str, inline-alloc
release paths, the direct fd write), all reached through console.log's
generic argument rendering. Outlining them to save one page would undo
the optimizations those PRs add.
The ceiling's documented intent is "several native pages of
linker-version slack" above a hello that the comment put at about 41KB.
That no longer held before this stack (64256 bytes on #743, 1.2 KiB of
slack). 80 KiB restores about three pages of slack over the stack's
largest hello and still catches lost section GC (the old always-linked
runtime was about 400KB). Symbol absence remains the primary
reachability contract. The Mach-O ceiling is unchanged.
Verified in the Linux x64 sandbox: pnpm test
tests/harness/runtime-tree-shaking.test.ts fails on #744 before this
change (68416 vs 65536) and passes after it, on #744 and on #764.