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Re: [ARM] getcontext routines v2


On Sat, Feb 25, 2012 at 4:39 AM, Carlos O'Donell <carlos@systemhalted.org> wrote:
On Thu, Feb 23, 2012 at 8:34 PM, Michael Hope <michael.hope@linaro.org> wrote:
This is an implementation of getcontext, makecontext, setcontext and
swapcontext for ARM Linux and continues on from Dave Gilbert's original
version[1].

The changes in this version are:
 * Use the GNU coding style
 * Use ucontext_i.sym to pull constants and struct offsets into the assembly
code
 * Match the style of the MIPS and Tile implementations

These routines survive basic testing.  A full GLIBC, QEMU, and GNU pth test
run is under way.

I looked over things briefly and the formatting and license looks OK. Do you and Dave have FSF copyright assignments in place?

Yes. Linaro has an assignment agreement for GCC, GDB, binutils, and GLIBC under case #664398.


I also have two comments.

(1) Is setcontext correctly implemented?

Your setcontext doesn't iterate over uc_link, instead you appear to rely
on makecontext having set a special return handler and input arguments.

The special return handler won't be set of the user manually sets uc_link
in the context, which I believe is an allowed operation (only uc_mcontext
is forbidden to be modified).

It's correct to the specification and matches the MIPS and Tile ports. From IEEE 1003.1:2004:


"""The uc_link member is used to determine the context that shall be resumed when the context being modified by makecontext() returns. The application shall ensure that the uc_link member is initialized prior to the call to makecontext()."""

There's no mention of uc_link being used except when the makecontext() child completes.

I've changed the function to __startcontext() to match the other ports and added a weak_alias on __makecontext for consistency.

I'd be interested in seeing if you pass all of the glibc tests.

There are no regressions between EGLIBC trunk and trunk + this patch. stdlib/bug-getcontext now passes. The (small) GNU pth testsuite passes.


(2) Please also post a GNU ChangeLog with your patches.

Done.


-- Michael

diff --git a/ChangeLog.arm b/ChangeLog.arm
index 9eef7e7..7ecb11b 100644
--- a/ChangeLog.arm
+++ b/ChangeLog.arm
@@ -1,3 +1,13 @@
+2012-02-27  Michael Hope  <michael.hope@linaro.org>
+
+	* sysdeps/unix/sysv/linux/arm/eabi/getcontext.S: New file.
+	* sysdeps/unix/sysv/linux/arm/eabi/makecontext.c: New file.
+	* sysdeps/unix/sysv/linux/arm/eabi/setcontext.S: New file.
+	* sysdeps/unix/sysv/linux/arm/eabi/swapcontext.S: New file.
+	* sysdeps/unix/sysv/linux/arm/ucontext_i.sym: New file.
+	* sysdeps/unix/sysv/linux/arm/Makefile (gen-as-const-headers): Add
+	ucontext_i.sym.
+
 2012-02-17  Aurelien Jarno  <aurelien@aurel32.net>

 	* sysdeps/arm/libm-test-ulps: Adjust ULPs for jn tests.
diff --git a/sysdeps/unix/sysv/linux/arm/Makefile b/sysdeps/unix/sysv/linux/arm/Makefile
index d91b968..a981736 100644
--- a/sysdeps/unix/sysv/linux/arm/Makefile
+++ b/sysdeps/unix/sysv/linux/arm/Makefile
@@ -20,3 +20,7 @@ endif
 ifeq ($(subdir),resource)
 sysdep_routines += oldgetrlimit64
 endif
+
+ifeq ($(subdir),stdlib)
+gen-as-const-headers += ucontext_i.sym
+endif
diff --git a/sysdeps/unix/sysv/linux/arm/eabi/getcontext.S b/sysdeps/unix/sysv/linux/arm/eabi/getcontext.S
new file mode 100644
index 0000000..11a49e3
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/eabi/getcontext.S
@@ -0,0 +1,114 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <sysdep.h>
+#include <rtld-global-offsets.h>
+
+#include "ucontext_i.h"
+
+	.syntax unified
+	.text
+
+/* int getcontext (ucontext_t *ucp) */
+
+ENTRY(__getcontext)
+	/* No need to save r0-r3, d0-d7, or d16-d31.  */
+	add	r1, r0, #MCONTEXT_ARM_R4
+	stmia   r1, {r4-r11}
+
+	/* Save R13 separately as Thumb can't STM it.  */
+	str     r13, [r0, #MCONTEXT_ARM_SP]
+	str     r14, [r0, #MCONTEXT_ARM_LR]
+	/* Return to LR */
+	str     r14, [r0, #MCONTEXT_ARM_PC]
+	/* Return zero */
+	mov     r2, #0
+	str     r2, [r0, #MCONTEXT_ARM_R0]
+
+	/* Save ucontext_t * across the next call.  */
+	mov	r4, r0
+	
+	/* __sigprocmask(SIG_BLOCK, NULL, &(ucontext->uc_sigmask)) */
+	mov     r0, #SIG_BLOCK
+	mov     r1, #0
+	add     r2, r4, #UCONTEXT_SIGMASK
+	bl      PLTJMP(__sigprocmask)
+	
+	/* Store FP regs.  Much of the FP code is copied from arm/eabi/setjmp.S.  */
+
+#ifdef PIC
+        ldr     r2, 1f
+        ldr     r1, Lrtld_global_ro
+0:      add     r2, pc, r2
+        ldr     r2, [r2, r1]
+        ldr     r2, [r2, #RTLD_GLOBAL_RO_DL_HWCAP_OFFSET]
+#else
+        ldr     r2, Lhwcap
+        ldr     r2, [r2, #0]
+#endif
+
+	add	r0, r4, #UCONTEXT_REGSPACE
+
+        tst     r2, #HWCAP_ARM_VFP
+        beq     Lno_vfp
+
+        /* Store the VFP registers.
+           Don't use VFP instructions directly because this code
+           is used in non-VFP multilibs.  */
+        /* Following instruction is vstmia r0!, {d8-d15}.  */
+        stc     p11, cr8, [r0], #64
+        /* Store the floating-point status register.  */
+        /* Following instruction is vmrs r1, fpscr.  */
+        mrc     p10, 7, r1, cr1, cr0, 0
+        str     r1, [r0], #4
+Lno_vfp:
+
+        tst     r2, #HWCAP_ARM_IWMMXT
+        beq     Lno_iwmmxt
+
+        /* Save the call-preserved iWMMXt registers.  */
+        /* Following instructions are wstrd wr10, [r0], #8 (etc.)  */
+        stcl    p1, cr10, [r0], #8
+        stcl    p1, cr11, [r0], #8
+        stcl    p1, cr12, [r0], #8
+        stcl    p1, cr13, [r0], #8
+        stcl    p1, cr14, [r0], #8
+        stcl    p1, cr15, [r0], #8
+Lno_iwmmxt:
+
+	/* Restore the clobbered R4 and LR.  */
+	ldr	r14, [r4, #MCONTEXT_ARM_LR]
+	ldr	r4, [r4, #MCONTEXT_ARM_R4]
+
+	mov	r0, #0
+
+	DO_RET(r14)
+
+END(__getcontext)
+
+#ifdef PIC
+1:      .long   _GLOBAL_OFFSET_TABLE_ - 0b - 8
+Lrtld_global_ro:
+        .long   C_SYMBOL_NAME(_rtld_global_ro)(GOT)
+#else
+Lhwcap:
+        .long   C_SYMBOL_NAME(_dl_hwcap)
+#endif
+
+
+weak_alias(__getcontext, getcontext)
diff --git a/sysdeps/unix/sysv/linux/arm/eabi/makecontext.c b/sysdeps/unix/sysv/linux/arm/eabi/makecontext.c
new file mode 100644
index 0000000..66f8456
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/eabi/makecontext.c
@@ -0,0 +1,74 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <stdarg.h>
+#include <ucontext.h>
+
+/* Number of arguments that go in registers.  */
+#define NREG_ARGS  4
+
+/* Take a context previously prepared via getcontext() and set to
+   call func() with the given int only args.  */
+void
+__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
+{
+  extern void __startcontext (void);
+  unsigned long *funcstack;
+  va_list vl;
+  unsigned long *regptr;
+  unsigned int reg;
+  int misaligned;
+
+  /* Start at the top of stack.  */
+  funcstack = (unsigned long *) (ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
+
+  /* Ensure the stack stays eight byte aligned.  */
+  misaligned = ((unsigned long) funcstack & 4) != 0;
+
+  if ((argc > NREG_ARGS) && (argc & 1) != 0)
+    misaligned = !misaligned;
+
+  if (misaligned)
+    funcstack -= 1;
+
+  va_start (vl, argc);
+
+  /* Reserve space for the on-stack arguments.  */
+  if (argc > NREG_ARGS)
+    funcstack -= (argc - NREG_ARGS);
+
+  ucp->uc_mcontext.arm_sp = (unsigned long) funcstack;
+  ucp->uc_mcontext.arm_pc = (unsigned long) func;
+
+  /* Exit to startcontext() with the next context in R4 */
+  ucp->uc_mcontext.arm_r4 = (unsigned long) ucp->uc_link;
+  ucp->uc_mcontext.arm_lr = (unsigned long) __startcontext;
+
+  /* The first four arguments go into registers.  */
+  regptr = &(ucp->uc_mcontext.arm_r0);
+
+  for (reg = 0; (reg < argc) && (reg < NREG_ARGS); reg++)
+    *regptr++ = va_arg (vl, unsigned long);
+
+  /* And the remainder on the stack.  */
+  for (; reg < argc; reg++)
+    *funcstack++ = va_arg (vl, unsigned long);
+
+  va_end (vl);
+}
+weak_alias (__makecontext, makecontext)
diff --git a/sysdeps/unix/sysv/linux/arm/eabi/setcontext.S b/sysdeps/unix/sysv/linux/arm/eabi/setcontext.S
new file mode 100644
index 0000000..f07af7f
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/eabi/setcontext.S
@@ -0,0 +1,102 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <sysdep.h>
+#include <rtld-global-offsets.h>
+
+#include "ucontext_i.h"
+
+	.syntax unified
+	.text
+
+/* int setcontext (const ucontext_t *ucp) */
+
+ENTRY(__setcontext)
+	mov	r4, r0
+	add	r0, r0, #UCONTEXT_REGSPACE
+
+        /* Restore the VFP registers.  Copied from arm/eabi/__longjmp.S.  */
+#ifdef PIC
+        ldr     r2, 1f
+        ldr     r1, Lrtld_global_ro
+0:      add     r2, pc, r2
+        ldr     r2, [r2, r1]
+        ldr     r2, [r2, #RTLD_GLOBAL_RO_DL_HWCAP_OFFSET]
+#else
+        ldr     r2, Lhwcap
+        ldr     r2, [r2, #0]
+#endif
+
+        tst     r2, #HWCAP_ARM_VFP
+        beq     Lno_vfp_sc
+
+        /* Following instruction is vldmia r0!, {d8-d15}.  */
+        ldc     p11, cr8, [r0], #64
+        /* Restore the floating-point status register.  */
+        ldr     r1, [r0], #4
+        /* Following instruction is fmxr fpscr, r1.  */
+        mcr     p10, 7, r1, cr1, cr0, 0
+Lno_vfp_sc:
+        tst     r2, #HWCAP_ARM_IWMMXT
+        beq     Lno_iwmmxt_sc
+
+        /* Restore the call-preserved iWMMXt registers.  */
+        /* Following instructions are wldrd wr10, [r0], #8 (etc.)  */
+        ldcl    p1, cr10, [r0], #8
+        ldcl    p1, cr11, [r0], #8
+        ldcl    p1, cr12, [r0], #8
+        ldcl    p1, cr13, [r0], #8
+        ldcl    p1, cr14, [r0], #8
+        ldcl    p1, cr15, [r0], #8
+Lno_iwmmxt_sc:
+
+	/* Now bring back the signal status.  */
+	mov	r0, #SIG_SETMASK
+	add	r1, r4, #UCONTEXT_SIGMASK
+	mov	r2, #0
+	bl	PLTJMP(__sigprocmask)
+
+        /* Loading r0-r3 makes makecontext easier.  */
+        add     r14, r4, #MCONTEXT_ARM_R0
+        ldmia   r14, {r0-r12}
+        ldr     r13, [r14, #(MCONTEXT_ARM_SP - MCONTEXT_ARM_R0)]
+        add     r14, r14, #(MCONTEXT_ARM_LR - MCONTEXT_ARM_R0)
+        ldmia   r14, {r14, pc}
+
+END(setcontext)
+weak_alias(__setcontext, setcontext)
+
+	/* Called when a makecontext() context returns.  Start the
+	   context in R4 or fall through to exit().  */
+ENTRY(__startcontext)
+        movs    r0, r4
+        bne     PLTJMP(__setcontext)
+
+        @ New context was 0 - exit
+        b       PLTJMP(_exit)
+END(__startcontext)
+
+#ifdef PIC
+1:      .long   _GLOBAL_OFFSET_TABLE_ - 0b - 8
+Lrtld_global_ro:
+        .long   C_SYMBOL_NAME(_rtld_global_ro)(GOT)
+#else
+Lhwcap:
+        .long   C_SYMBOL_NAME(_dl_hwcap)
+#endif
+
diff --git a/sysdeps/unix/sysv/linux/arm/eabi/swapcontext.S b/sysdeps/unix/sysv/linux/arm/eabi/swapcontext.S
new file mode 100644
index 0000000..efb881a
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/eabi/swapcontext.S
@@ -0,0 +1,64 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <sysdep.h>
+
+#include "ucontext_i.h"
+
+	.syntax unified
+	.text
+
+/* int swapcontext (ucontext_t *oucp, const ucontext_t *ucp) */
+
+ENTRY(swapcontext)
+
+	/* Have getcontext() do most of the work then fix up
+	   LR afterwards.  Save R3 to keep the stack aligned.  */
+	push	{r0,r1,r3,r14}
+	cfi_adjust_cfa_offset (16)
+	cfi_rel_offset (r0,0)
+	cfi_rel_offset (r1,4)
+	cfi_rel_offset (r3,8)
+	cfi_rel_offset (r14,12)
+
+	bl	__getcontext
+	mov	r4, r0
+
+	pop	{r0,r1,r3,r14}
+	cfi_adjust_cfa_offset (-16)
+	cfi_restore (r0)
+	cfi_restore (r1)
+	cfi_restore (r3)
+	cfi_restore (r14)
+
+	/* Exit if getcontext() failed.  */
+	cmp 	r4, #0
+	itt	ne
+	movne	r0, r4
+	RETINSTR(ne, r14)
+	
+	/* Fix up LR and the PC.  */
+	str	r13,[r0, #MCONTEXT_ARM_SP]
+	str	r14,[r0, #MCONTEXT_ARM_LR]
+	str	r14,[r0, #MCONTEXT_ARM_PC]
+
+	/* And swap using swapcontext().  */
+	mov	r0, r1
+	b	__setcontext
+
+END(swapcontext)
diff --git a/sysdeps/unix/sysv/linux/arm/ucontext_i.sym b/sysdeps/unix/sysv/linux/arm/ucontext_i.sym
new file mode 100644
index 0000000..306292f
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/ucontext_i.sym
@@ -0,0 +1,30 @@
+#include <inttypes.h>
+#include <signal.h>
+#include <stddef.h>
+#include <sys/ucontext.h>
+
+SIG_BLOCK
+SIG_SETMASK
+
+-- Offsets of the fields in the ucontext_t structure.
+#define ucontext(member)	offsetof (ucontext_t, member)
+#define mcontext(member)	ucontext (uc_mcontext.member)
+
+UCONTEXT_FLAGS			ucontext (uc_flags)
+UCONTEXT_LINK			ucontext (uc_link)
+UCONTEXT_STACK			ucontext (uc_stack)
+UCONTEXT_MCONTEXT		ucontext (uc_mcontext)
+UCONTEXT_SIGMASK		ucontext (uc_sigmask)
+
+UCONTEXT_REGSPACE		ucontext (uc_regspace)
+
+MCONTEXT_TRAP_NO		mcontext (trap_no)
+MCONTEXT_ERROR_CODE		mcontext (error_code)
+MCONTEXT_OLDMASK		mcontext (oldmask)
+MCONTEXT_ARM_R0			mcontext (arm_r0)
+MCONTEXT_ARM_R4			mcontext (arm_r4)
+MCONTEXT_ARM_SP			mcontext (arm_sp)
+MCONTEXT_ARM_LR			mcontext (arm_lr)
+MCONTEXT_ARM_PC			mcontext (arm_pc)
+MCONTEXT_ARM_CPSR		mcontext (arm_cpsr)
+MCONTEXT_FAULT_ADDRESS		mcontext (fault_address)


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