libc: make MINIX assembly code position-independent

While here, simplify ucontext.S

Author: antoineL

lib/libc/arch/i386/sys-minix/__sigreturn.S

@@ -5,5 +5,12 @@
 
 IMPORT(_sigreturn)
 ENTRY(__sigreturn)
+#ifndef PIC
 	addl	$16, %esp
 	jmp	_C_LABEL(_sigreturn)
+#else
+	addl	$16, %esp
+	PIC_PROLOGUE		/* push %ebx, but we do not care */
+	pop	%eax	/* special knowledge of how PIC works: discard pushed EBX */
+	jmp	PIC_PLT(_C_LABEL(_sigreturn))
+#endif /* PIC */

lib/libc/arch/i386/sys-minix/ucontext.S

@@ -1,26 +1,11 @@
 #include <machine/asm.h>
 #include <ucontextoffsets.h>
 
-#ifdef __ACK__
-.text
-begtext:
-#ifdef __ACK__
-.rom
-#else
-.data
-#endif
-begrom:
-.data
-begdata:
-.bss
-begbss:
-#endif
-
-
 IMPORT(getuctx)
 IMPORT(setuctx)
 IMPORT(resumecontext)
 
+	.globl	_C_LABEL(__errno)
 
 /* MCF_MAGIC value from <mcontext.h> */
 #define MCF_MAGIC	0xc0ffee
@@ -29,7 +14,6 @@ IMPORT(resumecontext)
 #define UCF_IGNFPU	0x002
 #define UCF_IGNSIGM	0x004
 
-
 /* EINVAL from errno.h */
 #define EFAULT		14
 #define EINVAL 		22
@@ -43,59 +27,44 @@ ENTRY(getcontext)
 	 * saving its signal mask, then we can skip the context switch to
 	 * PM and kernel altogether and only save general-purpose registers. */
 
-	mov (%esp), %ecx	/* Save return address:
-				 * When setcontext or swapcontext is called,
-				 * we jump to this address and continue
-				 * running. */
-
 	mov 4(%esp), %edx		/* edx = ucp */
 	/* Check null pointer */
 	cmp $0, %edx			/* edx == NULL? */
 	jne 3f				/* Not null, continue */
-	movl $EFAULT, (_C_LABEL(errno))
+	PIC_PROLOGUE
+	call PIC_PLT(_C_LABEL(__errno))
+	PIC_EPILOGUE
+	movl $EFAULT, (%eax)
 	xor %eax, %eax
 	dec %eax			/* return -1 */
 	ret
 
 3:	/* Check flags */
-	push %ecx			/* save ecx */
-	push %ebx			/* save ebx */
-	lea UC_FLAGS(%edx), %ebx	/* ebx = &(ucp->uc_flags) */
-	mov (%ebx), %ecx		/* ecx = ucp->uc_flags */
-	mov $UCF_IGNFPU, %eax
-	or $UCF_IGNSIGM, %eax
-	cmp %eax, %ecx			/* is UCF_IGNFPU or UCF_IGNSIGM set? */
-	pop %ebx			/* restore ebx */
-	pop %ecx			/* restore ecx */
-	jz 1f				/* Both are set, skip getuctx */
-
-0:
-	push %ecx			/* Save ecx */
+	mov UC_FLAGS(%edx), %eax	/* eax = ucp->uc_flags */
+#if 0
+	and $~[UCF_IGNFPU|UCF_IGNSIGM], %eax /* check only those flags */
+#endif
+	xor $[UCF_IGNFPU|UCF_IGNSIGM], %eax /* toggle both flags */
+	jz 5f				/* Both were set, skip getuctx */
+	PIC_PROLOGUE
 	push %edx		 
-	call _C_LABEL(getuctx)		/* getuctx(ucp) */
+	call PIC_PLT(_C_LABEL(getuctx))	/* getuctx(ucp) */
 	pop %edx			/* clean up stack and restore edx */
-	pop %ecx			/* Restore ecx */
+	PIC_EPILOGUE
 
-1: 
+5:
 	/* Save the context */
-	mov 4(%esp), %edx		/* edx = ucp */
-	pop %eax			/* retaddr */
-	mov %eax, PC(%edx)		/* Save real RTA in mcp struct */
+	pop PC(%edx)			/* Save real RTA in mcp struct */
 	mov %esp, SP(%edx)	/* Save stack pointer (now pointing to ucp) */
-	/* Save GP registers */
+	/* Save GP registers (except EAX and EDX) */
 	mov %ebp, BP(%edx)		/* Save EBP */
 	mov %esi, SI(%edx)		/* Save ESI */
 	mov %edi, DI(%edx)		/* Save EDI */
 	mov %ebx, BX(%edx)		/* Save EBX */
 	mov %ecx, CX(%edx)		/* Save ECX */
 	movl $MCF_MAGIC, MAGIC(%edx)	/* Set magic value */
-	push %eax			/* Restore retaddr */
-
 	xor %eax, %eax			/* Return 0 */
-
-2:	
-	add $4, %esp			/* Remove stale (setcontext) RTA */
-	jmp *%ecx			/* Restore return address */
+	jmp *PC(%edx)  			/* Return return address */
 
 
 /* int setcontext(const ucontext_t *ucp)
@@ -115,60 +84,60 @@ ENTRY(setcontext)
 	/* Check null pointer */
 	cmp $0, %edx			/* edx == NULL? */
 	jnz 3f				/* Not null, continue */
-	movl $EFAULT, (_C_LABEL(errno))
+	movl $EFAULT, %edx
+0:	PIC_PROLOGUE
+	call	PIC_PLT(_C_LABEL(__errno))
+	PIC_EPILOGUE
+	movl %edx, (%eax)
 	xor %eax, %eax
 	dec %eax			/* return -1 */
 	ret
 
 3:	/* Check flags */
-	push %ebx			/* save ebx */
-	lea MAGIC(%edx), %ebx		/* ebx = &(ucp->mc_context.mc_magic) */
-	mov (%ebx), %ecx		/* ecx = ucp->mc_context.mc_magic */
-	pop %ebx			/* restore ebx */
-	cmp $MCF_MAGIC, %ecx	/* is the magic value set (is context valid)?*/
+	cmpl $MCF_MAGIC, MAGIC(%edx)	/* is the magic value set (is context valid)?*/
 	jz 4f				/* is set, proceed */
-	movl $EINVAL, (_C_LABEL(errno)) /* not set, return error code */
-	xor %eax, %eax
-	dec %eax			/* return -1 */
-	ret	
+	movl $EINVAL, %edx		/* not set, return error code */
+	jmp 0b
 
 
-4:	push %ebx			/* save ebx */
-	lea UC_FLAGS(%edx), %ebx 	/* ebx = &(ucp->uc_flags) */
-	mov (%ebx), %ecx		/* ecx = ucp->uc_flags */
-	pop %ebx			/* restore ebx */
-	mov $UCF_IGNFPU, %eax
-	or $UCF_IGNSIGM, %eax
-	cmp %eax, %ecx		/* Are UCF_IGNFPU and UCF_IGNSIGM flags set? */
-	jz 1f			/* Both are set, so don't bother restoring FPU
+4:	mov UC_FLAGS(%edx), %eax	/* eax = ucp->uc_flags */
+#if 0
+	and $~[UCF_IGNFPU|UCF_IGNSIGM], %eax /* check only those flags */
+#endif
+	xor $[UCF_IGNFPU|UCF_IGNSIGM], %eax /* toggle both flags */
+	jz 5f			/* Both are set, so don't bother restoring FPU
 				 * state and signal mask */
 
-0:	push %ecx			/* Save ecx */
+	PIC_PROLOGUE
 	push %edx		 
-	call _C_LABEL(setuctx)		/* setuctx(ucp) */
+	call PIC_PLT(_C_LABEL(setuctx))	/* setuctx(ucp) */
 	pop %edx			/* Clean up stack and restore edx */
-	pop %ecx			/* Restore ecx */
+	PIC_EPILOGUE
 
-1:	/* Restore the registers */
-	mov 4(%esp), %edx		/* edx = ucp */
+5:	/* Restore the registers (except EAX and EDX) */
 	mov CX(%edx), %ecx		/* Restore ECX */
 	mov BX(%edx), %ebx		/* Restore EBX */
 	mov DI(%edx), %edi		/* Restore EDI */
 	mov SI(%edx), %esi		/* Restore ESI */
 	mov BP(%edx), %ebp		/* Restore EBP */
 	mov SP(%edx), %esp		/* Restore stack pointer */
-
-2:
+#if 0
 	jmp *PC(%edx)  	/* Push RTA onto stack so we can return to it */
-
+#else
+	jmp *PC(%edx)  			/* Return to RTA */
+#endif
 
 /* void ctx_start((void *func)(int arg1, ..., argn), arg1, ..., argn,
  *		  ucontext_t *ucp)
  *	A wrapper to start function `func'. ESI register will contain a pointer
  *	to ucp on the stack. By setting ESP to ESI, we effectively 'remove' all
  *	arguments to `func' from the stack. Finally, a call to resumecontext
  *	will start the next context in the linked list (or exit the program if
- *	there is no context). */
+ *	there is no context).
+ *
+ * Since PIC needs the EBX register, which is pushed on the stack by
+ * PIC_PROLOGUE, we need an extra of salsa here.
+ */
 ENTRY(ctx_start)
 	/* 0(esp) -> func
 	 * 4(esp) -> arg1
@@ -178,9 +147,10 @@ ENTRY(ctx_start)
 
 	pop %eax			/* eax = func */
 	call *%eax			/* func(arg1, ..., argn) */
-	mov %esi, %esp			/* Clean up stack */
+	PIC_PROLOGUE		/* may push %ebx, but we do not care */
+	mov %esi, %esp		/* Clean up stack, keep %ebx = &GOT */
 	/* ucp is now at the top of the stack again */
-	call _C_LABEL(resumecontext)	/* resumecontext(ucp) */
+	call PIC_PLT(_C_LABEL(resumecontext))	/* resumecontext(ucp) */
 	ret			/* never reached */