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Re: Proposed change to ppc32 ucontext_t


Ulrich Drepper writes:

> Paul Mackerras wrote:
> > Since we made the change to the ucontext_t on ppc32 to expand it to
> > include space for all of the registers, [...]
> 
> What's up with this?  Would the ppc people please make up their minds?

I haven't heard anything from Franz for ages.

I have made the corresponding changes to the implementation of
set/get/make/swapcontext.  With the patch below (against current glibc
cvs), glibc compiles cleanly and passes the stdlib/tst-setcontext
test.  (Some of the other tests are failing at the moment, but they
fail with or without this patch.)

In my opinion, this patch should go in.  I did the original *context
implementation for ppc32, including the changes to ucontext.h.  This
patch should solve the source compatibility problems that were
introduced by those changes.

In the absence of any comment from Franz, whose opinion would you
trust about ppc32 stuff?

Regards,
Paul.

diff -urN cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext.S libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext.S
--- cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext.S	2003-06-18 13:36:23.000000000 +1000
+++ libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext.S	2003-09-11 16:55:02.000000000 +1000
@@ -24,6 +24,13 @@
 #include "ucontext_i.h"
 
 ENTRY(__getcontext)
+	/*
+	 * Since we are not attempting to save the altivec registers,
+	 * there is no need to get the register storage space
+	 * aligned on a 16-byte boundary.
+	 */
+	addi	r3,r3,_UC_REG_SPACE
+	stw	r3,_UC_REGS_PTR - _UC_REG_SPACE(r3)
 	stw	r0,_UC_GREGS+(PT_R0*4)(r3)
 	stw	r1,_UC_GREGS+(PT_R1*4)(r3)
 	mflr	r0
@@ -112,7 +119,7 @@
 	stfd	fp31,_UC_FREGS+(31*8)(r3)
 	stfd	fp0,_UC_FREGS+(32*8)(r3)
 
-	addi	r5,r3,_UC_SIGMASK
+	addi	r5,r3,_UC_SIGMASK - _UC_REG_SPACE
 	li	r4,0
 	li	r3,SIG_BLOCK
 	bl	JUMPTARGET(sigprocmask)
diff -urN cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S
--- cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S	2003-06-18 13:36:38.000000000 +1000
+++ libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S	2003-09-12 13:04:41.000000000 +1000
@@ -25,22 +25,24 @@
 
 ENTRY(__makecontext)
 	/* Set up the first 7 args to the function in its registers */
-	stw	r6,_UC_GREGS+(PT_R3*4)(r3)
-	stw	r7,_UC_GREGS+(PT_R4*4)(r3)
-	stw	r8,_UC_GREGS+(PT_R5*4)(r3)
-	stw	r9,_UC_GREGS+(PT_R6*4)(r3)
-	stw	r10,_UC_GREGS+(PT_R7*4)(r3)
+	addi	r11,r3,_UC_REG_SPACE
+	stw	r11,_UC_REGS_PTR(r3)
+	stw	r6,_UC_GREGS+(PT_R3*4)(r11)
+	stw	r7,_UC_GREGS+(PT_R4*4)(r11)
+	stw	r8,_UC_GREGS+(PT_R5*4)(r11)
+	stw	r9,_UC_GREGS+(PT_R6*4)(r11)
+	stw	r10,_UC_GREGS+(PT_R7*4)(r11)
 	lwz	r8,8(r1)
 	lwz	r9,12(r1)
-	stw	r8,_UC_GREGS+(PT_R8*4)(r3)
-	stw	r9,_UC_GREGS+(PT_R9*4)(r3)
+	stw	r8,_UC_GREGS+(PT_R8*4)(r11)
+	stw	r9,_UC_GREGS+(PT_R9*4)(r11)
 
 	/* Set the NIP to the start of the function */
-	stw	r4,_UC_GREGS+(PT_NIP*4)(r3)
+	stw	r4,_UC_GREGS+(PT_NIP*4)(r11)
 
 	/* Set the function's r31 to ucp->uc_link for the exitcode below. */
 	lwz	r7,_UC_LINK(r3)
-	stw	r7,_UC_GREGS+(PT_R31*4)(r3)
+	stw	r7,_UC_GREGS+(PT_R31*4)(r11)
 
 	/* Set the function's LR to point to the exitcode below. */
 #ifdef PIC
@@ -53,7 +55,7 @@
 	lis	r6,L(exitcode)@ha
 	addi	r6,r6,L(exitcode)@l
 #endif
-	stw	r6,_UC_GREGS+(PT_LNK*4)(r3)
+	stw	r6,_UC_GREGS+(PT_LNK*4)(r11)
 
 	/*
 	 * Set up the stack frame for the function.
@@ -71,7 +73,7 @@
 	cmpwi	r5,8
 	blt	2f		/* less than 8 args is easy */
 	lwz	r10,16(r1)
-	stw	r10,_UC_GREGS+(PT_R10*4)(r3)
+	stw	r10,_UC_GREGS+(PT_R10*4)(r11)
 	beq	2f		/* if exactly 8 args */
 	subi	r9,r5,3
 	subi	r5,r5,8
@@ -83,7 +85,7 @@
 3:	lwzu	r10,4(r6)
 	stwu	r10,4(r8)
 	bdnz	3b
-2:	stw	r7,_UC_GREGS+(PT_R1*4)(r3)
+2:	stw	r7,_UC_GREGS+(PT_R1*4)(r11)
 	li	r6,0
 	stw	r6,0(r7)
 
diff -urN cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext.S libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext.S
--- cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext.S	2003-06-18 13:36:57.000000000 +1000
+++ libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext.S	2003-09-11 16:48:33.000000000 +1000
@@ -28,7 +28,7 @@
 	stwu	r1,-16(r1)
 	stw	r0,20(r1)
 	stw	r31,12(r1)
-	mr	r31,r3
+	lwz	r31,_UC_REGS_PTR(r3)
 
 	/*
 	 * If this ucontext refers to the point where we were interrupted
diff -urN cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/swapcontext.S libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/swapcontext.S
--- cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/swapcontext.S	2003-06-18 13:37:19.000000000 +1000
+++ libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/swapcontext.S	2003-09-11 16:55:13.000000000 +1000
@@ -25,6 +25,8 @@
 
 ENTRY(__swapcontext)
 	/* Save the current context */
+	addi	r3,r3,_UC_REG_SPACE
+	stw	r3,_UC_REGS_PTR - _UC_REG_SPACE(r3)
 	stw	r0,_UC_GREGS+(PT_R0*4)(r3)
 	stw	r1,_UC_GREGS+(PT_R1*4)(r3)
 	mflr	r0
@@ -115,7 +117,7 @@
 	stfd	fp31,_UC_FREGS+(31*8)(r3)
 	stfd	fp0,_UC_FREGS+(32*8)(r3)
 
-	addi	r5,r3,_UC_SIGMASK
+	addi	r5,r3,_UC_SIGMASK - _UC_REG_SPACE
 	addi	r4,r4,_UC_SIGMASK
 	li	r3,SIG_SETMASK
 	bl	JUMPTARGET(sigprocmask)
@@ -133,6 +135,8 @@
 	 * r0, xer, ctr.  We don't restore r2 since it will be used as
 	 * the TLS pointer.
 	 */
+	mr	r4,r31
+	lwz	r31,_UC_REGS_PTR(r31)
 	lwz	r0,_UC_GREGS+(PT_MSR*4)(r31)
 	cmpwi	r0,0
 	bne	L(do_sigret)
@@ -223,7 +227,7 @@
 	blr
 
 L(do_sigret):
-	addi	r1,r31,-0xd0
+	addi	r1,r4,-0xd0
 	li	r0,SYS_ify(rt_sigreturn)
 	sc
 	/* NOTREACHED */
diff -urN cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/ucontext_i.h libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/ucontext_i.h
--- cvs/libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/ucontext_i.h	2003-06-18 13:37:33.000000000 +1000
+++ libc/sysdeps/unix/sysv/linux/powerpc/powerpc32/ucontext_i.h	2003-09-11 16:48:08.000000000 +1000
@@ -24,7 +24,11 @@
 #define _UC_LINK	4
 #define _UC_STACK_SP	8
 #define _UC_STACK_SIZE	16
-#define _UC_SIGMASK	64
-#define _UC_GREGS	192
-#define _UC_FREGS	384
-#define _UC_VREGS	656
+#define _UC_REGS_PTR	48
+#define _UC_SIGMASK	52
+#define _UC_REG_SPACE	180
+
+/* offsets within mcontext_t */
+#define _UC_GREGS	0
+#define _UC_FREGS	192
+#define _UC_VREGS	464
diff -urN cvs/libc/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h libc/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h
--- cvs/libc/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h	2003-07-04 10:12:48.000000000 +1000
+++ libc/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h	2003-09-11 16:31:52.000000000 +1000
@@ -74,14 +74,40 @@
     struct ucontext *uc_link;
     stack_t uc_stack;
 #if __WORDSIZE == 32
-    /* These fields are for backwards compatibility. */
+    /*
+     * These fields are set up this way to maximize source and
+     * binary compatibility with code written for the old
+     * ucontext_t definition, which didn't include space for the
+     * registers.
+     *
+     * Different versions of the kernel have stored the registers on
+     * signal delivery at different offsets from the ucontext struct.
+     * Programs should thus use the uc_mcontext.uc_regs pointer to
+     * find where the registers are actually stored.  The registers
+     * will be stored within the ucontext_t struct but not necessarily
+     * at a fixed address.  As a side-effect, this lets us achieve
+     * 16-byte alignment for the register storage space if the
+     * Altivec registers are to be saved, without requiring 16-byte
+     * alignment on the whole ucontext_t.
+     *
+     * The uc_mcontext.regs field is included for source compatibility
+     * with programs written against the older ucontext_t definition,
+     * and its name should therefore not change.  The uc_pad field
+     * is for binary compatibility with programs compiled against the
+     * old ucontext_t; it ensures that uc_mcontext.regs and uc_sigmask
+     * are at the same offset as previously.
+     */
     int uc_pad[7];
-    mcontext_t *uc_regs;
-    unsigned int uc_oldsigmask[2];
-    int uc_pad2;
-#endif
+    union uc_regs_ptr {
+      struct pt_regs *regs;
+      mcontext_t *uc_regs;
+    } uc_mcontext;
+    sigset_t    uc_sigmask;
+    char uc_reg_space[sizeof(mcontext_t) + 12];  /* last for extensibility */
+#else /* 64-bit */
     sigset_t    uc_sigmask;
     mcontext_t  uc_mcontext;  /* last for extensibility */
+#endif
   } ucontext_t;
 
 #endif /* sys/ucontext.h */


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