feat: extend ata with Bitmap

include/elf.h

@@ -33,4 +33,60 @@ typedef struct Elf64ProgramHeader {
 
 uint64 elfLoad(const void* image, uint64 imageSize);
 
+/* Maps one ELF64 program header's p_flags (segmentFlags: standard PF_X=1/
+   PF_W=2/PF_R=4 bit values) onto the extra paging.h leaf-PTE bits
+   (pageWrite, pageNoExecute) elfLoad passes to pagingMapUserRangeExact for
+   that segment -- real per-segment W^X (a binary's own .text/.rodata ends
+   up read-only+executable, its .data/.bss read-write+non-executable)
+   instead of one blanket writable+executable range for the whole image.
+   Pure address-flag arithmetic, no paging/scheduler/VFS state touched, so
+   it is fully unit-testable (elfTest.c) the same way elfSlotBase and
+   friends already are. */
+uint64 elfSegmentPagingFlags(uint32 segmentFlags);
+
+/* Every userspace binary in this kernel is linked (Makefile --defsym
+   USER_BASE=...) at a fixed, elfSlotSize-aligned base of its own, since
+   there is one shared address space system-wide (no per-process page
+   tables/CR3) and no relocation support (-fno-pic): two binaries must
+   simply never overlap. kmain.c's boot-time spawnUser calls hardcode each
+   binary's stack/brk address following the same base+offset pattern by
+   hand; elfSlotStackTop/elfSlotBrkStart let syscall.c's exec()/spawn()
+   (a path resolved at runtime, not known at kmain.c's compile time)
+   derive the same addresses purely from the ELF's own entry point. */
+#define elfSlotSize        0x10000000ull
+#define elfSlotStackOffset 0x08000000ull
+#define elfSlotBrkOffset   0x04000000ull
+
+uint64 elfSlotBase(uint64 entry);
+uint64 elfSlotStackTop(uint64 entry);
+uint64 elfSlotBrkStart(uint64 entry);
+
+/* Ceiling on argv entries any single exec()/spawn()/boot launch can pass
+   (syscall.c's copyUserArgv enforces the same bound while copying them out
+   of userspace). Chosen together with the 256-byte per-argument cap
+   syscall.c already uses for path-like strings so that
+   elfMaxArgs*256 + a few hundred bytes of pointers/argc never comes close
+   to execStackSize (syscall.c) or kmain.c's userStackSize -- both far
+   larger than any realistic argv list this kernel's own binaries pass. */
+#define elfMaxArgs 16
+
+/* Lays out a process's very first stack frame the way a real x86_64 SysV
+   process entry looks (used by user/crt.S's _start): from stackTop down,
+   the argument strings themselves, then (16-byte aligned per the ABI)
+   argc, argv[0..argc-1], and a NULL argv terminator -- *outRsp is where
+   _start should start executing with, pointing at argc.
+   argv/argc are already kernel-side data (copyUserArgv, doExec/doSpawn in
+   syscall.c, or a literal array for kmain.c's boot spawnUser) by the time
+   this runs; this function only ever writes into [stackTop-stackSize,
+   stackTop), which the caller must have already mapped (pagingMapUserRange)
+   -- same contract as elfLoad's segment writes.
+   Returns false, writing nothing, if argc is out of [0, elfMaxArgs] or the
+   strings plus the fixed-size argv/argc area do not fit in stackSize bytes
+   -- unreachable for every call site in this kernel today given the bound
+   above, but checked rather than assumed so a future caller with a bigger
+   argv (or a deliberately tiny stack in elfTest.c) fails cleanly instead of
+   silently writing before stackTop-stackSize. */
+bool elfBuildInitialStack(uint64 stackTop, uint64 stackSize, const char* const* argv,
+                           int argc, uint64* outRsp);
+
 #endif