New runtime library: libchkstk

Provides 32-bit and 64-bit ___chkstk_ms and __chkstk. The former can
replace the libgcc implementation. Better license, about half the size,
and substantially faster when used on a hot path. The purpose and role
is similar to libmemory.

Dockerfile

@@ -59,7 +59,7 @@ RUN sha256sum -c $PREFIX/src/SHA256SUMS \
  && tar xJf nasm-$NASM_VERSION.tar.xz \
  && tar xjf vim-$VIM_VERSION.tar.bz2 \
  && tar xzf cppcheck-$CPPCHECK_VERSION.tar.gz
-COPY src/w64devkit.c src/w64devkit.ico src/libmemory.c \
+COPY src/w64devkit.c src/w64devkit.ico src/libmemory.c src/libchkstk.S \
      src/alias.c src/debugbreak.c src/pkg-config.c src/vc++filt.c \
      $PREFIX/src/
 
@@ -126,7 +126,9 @@ ENV PATH="/bootstrap/bin:${PATH}"
 
 RUN mkdir -p $PREFIX/$ARCH/lib \
  && CC=$ARCH-gcc DESTDIR=$PREFIX/$ARCH/lib/ sh $PREFIX/src/libmemory.c \
- && ln $PREFIX/$ARCH/lib/libmemory.a /bootstrap/$ARCH/lib/
+ && ln $PREFIX/$ARCH/lib/libmemory.a /bootstrap/$ARCH/lib/ \
+ && CC=$ARCH-gcc DESTDIR=$PREFIX/$ARCH/lib/ sh $PREFIX/src/libchkstk.S \
+ && ln $PREFIX/$ARCH/lib/libchkstk.a /bootstrap/$ARCH/lib/
 
 WORKDIR /x-mingw-crt
 RUN /mingw-w64-v$MINGW_VERSION/mingw-w64-crt/configure \

README.md

@@ -73,6 +73,12 @@ executables. Unique to w64devkit, `libmemory.a` is a library of `memset`,
 instructions. When [not linking a CRT][crt], linking `-lmemory` provides
 tiny definitions, particularly when GCC requires them.
 
+Also unique to w64devkit, `libchkstk.a` has a leaner, faster definition of
+`___chkstk_ms` than GCC (`-lgcc`), as well as `__chkstk`, sometimes needed
+when linking MSVC artifacts. Both are in the public domain and so, unlike
+default implementations, do not involve complex licensing. When required
+in a `-nostdlib` build, link `-lchkstk`.
+
 ## Fortran support
 
 Only C and C++ are included by default, but w64devkit also has full

src/libchkstk.S

@@ -0,0 +1,82 @@
+#if 0
+# Implementations of ___chkstk_ms (GCC) and __chkstk (MSVC). Unlike
+# libgcc, no work happens if the stack is already committed. Execute
+# this source with a shell to build libchkstk.a.
+# This is free and unencumbered software released into the public domain.
+set -ex
+${CC:-cc} -c -DCHKSTK_MS -Wa,--no-pad-sections -o chkstk_ms.o $0
+${CC:-cc} -c -DCHKSTK    -Wa,--no-pad-sections -o chkstk.o    $0
+rm -f "${DESTDIR}libchkstk.a"
+ar r "${DESTDIR}libchkstk.a" chkstk_ms.o chkstk.o
+rm chkstk_ms.o chkstk.o
+exit 0
+#endif
+
+#if __amd64
+// On x64, ___chkstk_ms and __chkstk have identical semantics. Unlike
+// x86 __chkstk, neither adjusts the stack pointer. This implementation
+// preserves all registers.
+//
+// The frame size is passed in rax, and this function ensures that
+// enough of the stack is committed for the frame. It commits stack
+// pages by writing to the guard page, one page at a time.
+#  if CHKSTK_MS
+	.globl ___chkstk_ms
+___chkstk_ms:
+#  elif CHKSTK
+	.globl __chkstk
+__chkstk:
+#  endif
+	push %rax
+	push %rcx
+	neg  %rax		// rax = frame low address
+	add  %rsp, %rax		// "
+	mov  %gs:(0x10), %rcx	// rcx = stack low address
+	jmp  1f
+0:	sub  $0x1000, %rcx	// extend stack into guard page
+	test %eax, (%rcx)	// commit page (two instruction bytes)
+1:	cmp  %rax, %rcx
+	ja   0b
+	pop  %rcx
+	pop  %rax
+	ret
+#endif  // __amd64
+
+#if __i386
+#  if CHKSTK_MS
+// Behaves exactly like x64 ___chkstk_ms.
+	.globl ___chkstk_ms
+___chkstk_ms:
+	push %eax
+	push %ecx
+	neg  %eax		// eax = frame low address
+	add  %esp, %eax		// "
+	mov  %fs:(0x08), %ecx	// ecx = stack low address
+	jmp  1f
+0:	sub  $0x1000, %ecx	// extend stack into guard page
+	test %eax, (%ecx)	// commit page (two instruction bytes)
+1:	cmp  %eax, %ecx
+	ja   0b
+	sub  %esp, %eax
+	pop  %ecx
+	pop  %eax
+	ret
+#  elif CHKSTK
+// On x86, __chkstk allocates the new stack frame. This implementation
+// clobbers eax. MSVC only seems to care about ebp and ecx (this).
+	.globl __chkstk
+__chkstk:
+	push %ecx		// preserve ecx
+	neg  %eax		// eax = frame low address
+	lea  8(%esp,%eax), %eax	// "
+	mov  %fs:(0x08), %ecx	// ecx = stack low address
+	jmp  1f
+0:	sub  $0x1000, %ecx	// extend stack into guard page
+	test %eax, (%ecx)	// commit page (two instruction bytes)
+1:	cmp  %eax, %ecx
+	ja   0b
+	pop  %ecx		// restore ecx
+	xchg %eax, %esp		// allocate frame
+	jmp  *(%eax)		// return
+#  endif
+#endif  // __i386