xtensa: add support for TLS

The Xtensa architecture provides a global register called THREADPTR
for the purpose of Thread Local Storage (TLS) support. This allows us
to use a fairly simple implementation, keeping the thread pointer in
the regset and simply saving and restoring it upon entering/exiting
the from user space.

Signed-off-by: Chris Zankel <chris@zankel.net>

7 files changed, 25 insertions, 7 deletions

diff --git a/arch/xtensa/include/asm/elf.h b/arch/xtensa/include/asm/elf.h
index 264d5fa450d8..eacb25a41718 100644
--- a/arch/xtensa/include/asm/elf.h
+++ b/arch/xtensa/include/asm/elf.h
@@ -84,7 +84,8 @@ typedef struct {
         elf_greg_t sar;
         elf_greg_t windowstart;
         elf_greg_t windowbase;
-        elf_greg_t reserved[8+48];
+        elf_greg_t threadptr;
+        elf_greg_t reserved[7+48];
         elf_greg_t a[64];
 } xtensa_gregset_t;
 
diff --git a/arch/xtensa/include/asm/ptrace.h b/arch/xtensa/include/asm/ptrace.h
index 682b1deac1f2..81f31bc9dde0 100644
--- a/arch/xtensa/include/asm/ptrace.h
+++ b/arch/xtensa/include/asm/ptrace.h
@@ -38,6 +38,7 @@ struct pt_regs {
         unsigned long syscall;          /*  56 */
         unsigned long icountlevel;      /*  60 */
         unsigned long scompare1;        /*  64 */
+        unsigned long threadptr;        /*  68 */
 
         /* Additional configurable registers that are used by the compiler. */
         xtregs_opt_t xtregs_opt;
@@ -48,7 +49,7 @@ struct pt_regs {
         /* current register frame.
          * Note: The ESF for kernel exceptions ends after 16 registers!
          */
-        unsigned long areg[16];         /* 128 (64) */
+        unsigned long areg[16];
 };
 
 #include <variant/core.h>
diff --git a/arch/xtensa/kernel/asm-offsets.c b/arch/xtensa/kernel/asm-offsets.c
index 0701fad170db..1915c7c889ba 100644
--- a/arch/xtensa/kernel/asm-offsets.c
+++ b/arch/xtensa/kernel/asm-offsets.c
@@ -42,6 +42,7 @@ int main(void)
         DEFINE(PT_ICOUNTLEVEL, offsetof (struct pt_regs, icountlevel));
         DEFINE(PT_SYSCALL, offsetof (struct pt_regs, syscall));
         DEFINE(PT_SCOMPARE1, offsetof(struct pt_regs, scompare1));
+        DEFINE(PT_THREADPTR, offsetof(struct pt_regs, threadptr));
         DEFINE(PT_AREG, offsetof (struct pt_regs, areg[0]));
         DEFINE(PT_AREG0, offsetof (struct pt_regs, areg[0]));
         DEFINE(PT_AREG1, offsetof (struct pt_regs, areg[1]));
diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 70d5a9e33573..63845f950792 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -130,6 +130,11 @@ _user_exception:
         s32i    a3, a1, PT_SAR
         s32i    a2, a1, PT_ICOUNTLEVEL
 
+#if XCHAL_HAVE_THREADPTR
+        rur     a2, threadptr
+        s32i    a2, a1, PT_THREADPTR
+#endif
+
         /* Rotate ws so that the current windowbase is at bit0. */
         /* Assume ws = xxwww1yyyy. Rotate ws right, so that a2 = yyyyxxwww1 */
 
@@ -510,6 +515,11 @@ user_exception_exit:
          *       (if we have restored WSBITS-1 frames).
          */
 
+#if XCHAL_HAVE_THREADPTR
+        l32i    a3, a1, PT_THREADPTR
+        wur     a3, threadptr
+#endif
+
 2:      j       common_exception_exit
 
         /* This is the kernel exception exit.
@@ -1955,7 +1965,7 @@ ENTRY(_switch_to)
         s32i    a6, a3, EXC_TABLE_FIXUP
         s32i    a7, a3, EXC_TABLE_KSTK
 
-        /* restore context of the task that 'next' addresses */
+        /* restore context of the task 'next' */
 
         l32i    a0, a13, THREAD_RA      # restore return address
         l32i    a1, a13, THREAD_SP      # restore stack pointer
diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c
index 0dd5784416d3..5cd82e9f601c 100644
--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -259,9 +259,10 @@ int copy_thread(unsigned long clone_flags, unsigned long usp_thread_fn,
                         memcpy(&childregs->areg[XCHAL_NUM_AREGS - len/4],
                                &regs->areg[XCHAL_NUM_AREGS - len/4], len);
                 }
-// FIXME: we need to set THREADPTR in thread_info...
+
+                /* The thread pointer is passed in the '4th argument' (= a5) */
                 if (clone_flags & CLONE_SETTLS)
-                        childregs->areg[2] = childregs->areg[6];
+                        childregs->threadptr = childregs->areg[5];
         } else {
                 p->thread.ra = MAKE_RA_FOR_CALL(
                                 (unsigned long)ret_from_kernel_thread, 1);
diff --git a/arch/xtensa/kernel/ptrace.c b/arch/xtensa/kernel/ptrace.c
index a8b0d5795571..562fac664751 100644
--- a/arch/xtensa/kernel/ptrace.c
+++ b/arch/xtensa/kernel/ptrace.c
@@ -66,6 +66,7 @@ int ptrace_getregs(struct task_struct *child, void __user *uregs)
         __put_user(regs->lcount, &gregset->lcount);
         __put_user(regs->windowstart, &gregset->windowstart);
         __put_user(regs->windowbase, &gregset->windowbase);
+        __put_user(regs->threadptr, &gregset->threadptr);
 
         for (i = 0; i < XCHAL_NUM_AREGS; i++)
                 __put_user(regs->areg[i],
@@ -92,6 +93,7 @@ int ptrace_setregs(struct task_struct *child, void __user *uregs)
         __get_user(regs->lcount, &gregset->lcount);
         __get_user(ws, &gregset->windowstart);
         __get_user(wb, &gregset->windowbase);
+        __get_user(regs->threadptr, &gregset->threadptr);
 
         regs->ps = (regs->ps & ~ps_mask) | (ps & ps_mask) | (1 << PS_EXCM_BIT);
 
diff --git a/arch/xtensa/kernel/signal.c b/arch/xtensa/kernel/signal.c
index de34d6be91cd..6952d8959236 100644
--- a/arch/xtensa/kernel/signal.c
+++ b/arch/xtensa/kernel/signal.c
@@ -337,7 +337,7 @@ static int setup_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         struct rt_sigframe *frame;
         int err = 0;
         int signal;
-        unsigned long sp, ra;
+        unsigned long sp, ra, tp;
 
         sp = regs->areg[1];
 
@@ -395,7 +395,8 @@ static int setup_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
          * Return context not modified until this point.
          */
 
-        /* Set up registers for signal handler */
+        /* Set up registers for signal handler; preserve the threadptr */
+        tp = regs->threadptr;
         start_thread(regs, (unsigned long) ka->sa.sa_handler,
                      (unsigned long) frame);
 
@@ -406,6 +407,7 @@ static int setup_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         regs->areg[6] = (unsigned long) signal;
         regs->areg[7] = (unsigned long) &frame->info;
         regs->areg[8] = (unsigned long) &frame->uc;
+        regs->threadptr = tp;
 
         /* Set access mode to USER_DS.  Nomenclature is outdated, but
          * functionality is used in uaccess.h