Hojun-Cho
4ab530c24d
Capture envp from the kernel-supplied stack into a DATAW slot during
_start's prologue (before CALL main), and expose it via a `rt_envp`
TEXT getter. lib/os.getenv binds the getter as `@symbol("rt_envp")
fn rtenvp() **u8` — the getter-fn pattern works around @symbol-on-let
not being supported by the compiler yet (silent miscompile otherwise).
`os.getenv(name: str) (str | void)` matches Hare's os::getenv surface:
walks the NUL-terminated envp table, "name=" prefix-matches with an
explicit `=` boundary check so prefixes don't false-match longer
names, returns the value as a borrowed str view. Empty value (env
"FOO=") returns len=0 str, not void — void is reserved for "name
not present at all".
Cohort coverage in lib/os/ostest.ww + test/wcc/974_getenv_run.c:
set / empty / unset / prefix-no-match (4 @test fns).
49 lines
2.1 KiB
ArmAsm
49 lines
2.1 KiB
ArmAsm
// rt/start.s — process entry. Linux sets up the stack so that on
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// entry [SP] holds argc, [SP+8] starts argv (NULL-terminated array
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// of *u8), [SP+8+(argc+1)*8] starts envp (also NULL-terminated).
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//
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// We pull argc into DI and the argv pointer into SI, then jump to
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// `main`. ww programs that declare `fn main(argc: i32, argv: **u8)
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// i32` see them; programs declaring `fn main() i32` simply ignore
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// the regs. Either way, main's return value is fed to the exit
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// syscall.
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//
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// envp is captured into the rt_envp_slot DATAW cell before CALL main
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// so lib/os.getenv (via the rt_envp getter below) can walk it. We
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// compute envp = SP + 16 + argc*8 in AX using three doublings and
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// adds — w6a's syntax doesn't ship SIB-style indexed addressing
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// (no `LEAQ 16(SP)(DI*8), AX`), so the explicit shift-by-three is
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// the portable form. AX/DI/SI are scratch on entry; no callee-
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// saved discipline applies until we reach main.
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TEXT _start,$0
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MOVQ (SP), DI // argc → DI (1st arg to main)
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LEAQ 8(SP), SI // &argv[0] → SI (2nd arg to main)
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MOVQ DI, AX // AX = argc
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ADDQ AX, AX // AX = argc * 2
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ADDQ AX, AX // AX = argc * 4
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ADDQ AX, AX // AX = argc * 8
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ADDQ SP, AX // AX = SP + argc*8
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ADDQ $16, AX // AX = SP + argc*8 + 16 = &argv[argc+1] = envp
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MOVQ AX, rt_envp_slot(SB)
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CALL main(SB)
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MOVQ AX, DI
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MOVQ $60, AX
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SYSCALL
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// rt_envp — getter that returns the envp pointer captured at process
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// entry. Bound from lib/os via `@symbol("rt_envp") fn rtenvp() **u8;`,
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// matching the rt_syscall / rt_alloc / rt_abort pattern. Read-only
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// view of the kernel-supplied table; the bytes live for the process
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// lifetime. A future setenv that grows the table re-points the slot
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// (separate task).
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TEXT rt_envp,$0
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MOVQ rt_envp_slot(SB), AX
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RET
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// rt_envp_slot — 8-byte writable cell holding the envp pointer.
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// Initialised to zero in .data; _start overwrites it before
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// transferring control to main. DATAW gives us the writable .data
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// slot (w6a has no GLOBL; same shape as lib/log's silent/default/
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// global cells in lib/log/log.s).
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DATAW rt_envp_slot(SB),"\x00\x00\x00\x00\x00\x00\x00\x00"
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