As a reference for anyone interested, attached you find a patch for the
user context switching routines that does work properly.
Note that it only (re)stores the basic set of registers, not the
floating point or IWMMXT registers.
Have fun while using it!
-- Timon
--- a/Makefile.in 2012-06-26 11:06:17.989987413 +0200
+++ b/Makefile.in 2012-06-26 11:05:02.517987412 +0200
@@ -165,6 +165,9 @@ headers: $(top_builddir)include/bits/uCl
subdirs: $(addprefix $(top_builddir),$(subdirs))
pregen-headers: $(top_builddir)include/bits/sysnum.h $(pregen-headers-y)
pregen: headers pregen-headers
+ifeq ($(UCLIBC_HAS_CONTEXT_FUNCS),y)
+ $(Q)$(MAKE) libc_arch_headers
+endif
$(Q)$(if $(UCLIBC_HAS_LOCALE),$(MAKE) -C extra/locale locale_headers)
$(top_builddir)include/bits/sysnum.h: $(top_srcdir)extra/scripts/gen_bits_syscall_h.sh | $(top_builddir)include/bits
--- a/include/ucontext.h 2012-05-15 09:20:09.000000000 +0200
+++ b/include/ucontext.h 2012-06-26 10:45:46.389987413 +0200
@@ -16,6 +16,8 @@
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
+/* System V ABI compliant user-level context switching support. */
+
#ifndef _UCONTEXT_H
#define _UCONTEXT_H 1
@@ -24,9 +26,28 @@
/* Get machine dependent definition of data structures. */
#include <sys/ucontext.h>
-/* The System V ABI user-level context switching support functions
- * are marked obsolescent by SuSv3, and are not implemented by
- * uClibc. This header is therefore empty. */
+__BEGIN_DECLS
+
+/* Get user context and store it in variable pointed to by UCP. */
+extern int getcontext (ucontext_t *__ucp) __THROW;
+
+/* Set user context from information of variable pointed to by UCP. */
+extern int setcontext (__const ucontext_t *__ucp) __THROW;
+
+/* Save current context in context variable pointed to by OUCP and set
+ context from variable pointed to by UCP. */
+extern int swapcontext (ucontext_t *__restrict __oucp,
+ __const ucontext_t *__restrict __ucp) __THROW;
+
+/* Manipulate user context UCP to continue with calling functions FUNC
+ and the ARGC-1 parameters following ARGC when the context is used
+ the next time in `setcontext' or `swapcontext'.
+
+ We cannot say anything about the parameters FUNC takes; `void'
+ is as good as any other choice. */
+extern void makecontext (ucontext_t *__ucp, void (*__func) (void),
+ int __argc, ...) __THROW;
+__END_DECLS
#endif /* ucontext.h */
--- a/libc/sysdeps/linux/arm/getcontext.S 1970-01-01 01:00:00.000000000 +0100
+++ b/libc/sysdeps/linux/arm/getcontext.S 2012-06-26 10:44:33.997987413 +0200
@@ -0,0 +1,58 @@
+/* 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, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <sysdep.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)
+
+ /* 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)
+weak_alias(__getcontext, getcontext)
--- a/libc/sysdeps/linux/arm/makecontext.c 1970-01-01 01:00:00.000000000 +0100
+++ b/libc/sysdeps/linux/arm/makecontext.c 2012-06-26 10:44:33.997987413 +0200
@@ -0,0 +1,73 @@
+/* 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, see
+ <http://www.gnu.org/licenses/>. */
+
+#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)
--- a/libc/sysdeps/linux/arm/Makefile.arch 2012-05-15 09:20:09.000000000 +0200
+++ b/libc/sysdeps/linux/arm/Makefile.arch 2012-06-26 10:52:48.569987412 +0200
@@ -12,6 +12,31 @@ SSRC := \
bsd-_setjmp.S sigrestorer.S mmap64.S \
vfork.S clone.S
+ifeq ($(UCLIBC_HAS_CONTEXT_FUNCS),y)
+CSRC += makecontext.c
+SSRC += getcontext.S setcontext.S swapcontext.S
+
+LIBC_ARCH_DIR := $(top_srcdir)/libc/sysdeps/linux/$(TARGET_ARCH)
+LIBC_ARCH_OUT := $(top_builddir)/libc/sysdeps/linux/$(TARGET_ARCH)
+
+libc_arch_headers : $(LIBC_ARCH_OUT)/ucontext_i.h
+headers_clean-y += libc_arch_headers_clean
+
+CFLAGS-ucontext_i.c = -S
+
+$(LIBC_ARCH_OUT)/ucontext_i.c: $(LIBC_ARCH_DIR)/ucontext_i.sym
+ $(do_awk) $(top_srcdir)extra/scripts/gen-as-const.awk $< > $@
+
+$(LIBC_ARCH_OUT)/ucontext_i.s: $(LIBC_ARCH_OUT)/ucontext_i.c
+ $(compile.c)
+
+$(LIBC_ARCH_OUT)/ucontext_i.h: $(LIBC_ARCH_OUT)/ucontext_i.s
+ $(do_sed) -n "s/^.*@@@name@@@\([^@]*\)@@@value@@@[^0-9Xxa-fA-F-]*\([0-9Xxa-fA-F-][0-9Xxa-fA-F-]*\).*@@@end@@@.*$\/#define \1 \2/p" $< > $@
+
+libc_arch_headers_clean:
+ $(do_rm) $(addprefix $(LIBC_ARCH_OUT)/ucontext_i., c h s)
+endif
+
ifeq ($(UCLIBC_HAS_THREADS_NATIVE),y)
SSRC += libc-aeabi_read_tp.S libc-thumb_atomics.S
endif
--- a/libc/sysdeps/linux/arm/setcontext.S 1970-01-01 01:00:00.000000000 +0100
+++ b/libc/sysdeps/linux/arm/setcontext.S 2012-06-26 10:44:33.997987413 +0200
@@ -0,0 +1,54 @@
+/* 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, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <sysdep.h>
+
+#include "ucontext_i.h"
+
+ .syntax unified
+ .text
+
+/* int setcontext (const ucontext_t *ucp) */
+
+ENTRY(__setcontext)
+ mov r4, r0
+
+ /* 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-r11}
+ 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)
--- a/libc/sysdeps/linux/arm/swapcontext.S 1970-01-01 01:00:00.000000000 +0100
+++ b/libc/sysdeps/linux/arm/swapcontext.S 2012-06-26 10:44:33.997987413 +0200
@@ -0,0 +1,63 @@
+/* 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, see
+ <http://www.gnu.org/licenses/>. */
+
+#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)
--- a/libc/sysdeps/linux/arm/ucontext_i.sym 1970-01-01 01:00:00.000000000 +0100
+++ b/libc/sysdeps/linux/arm/ucontext_i.sym 2012-06-26 10:46:46.001987413 +0200
@@ -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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