* Nicolas Pitre <nico@xxxxxxxxxxx> [100629 22:14]:
> On Tue, 29 Jun 2010, Tony Lindgren wrote:
>
> > Also, can we detect somehow the hardware that uses CONFIG_TLS_REG_EMUL?
> > Might be possible to remove that Kconfig option too later on..
>
> Well... I don't think we _should_ try to detect it as it is not widely
> available if at all.
OK
> And there is actually a "bug" with __kuser_get_tls because if ever
> CONFIG_TLS_REG_EMUL is selected then a call to __kuser_get_tls is
> currently doing nothing while it should actually use the mrc
> instruction.
I've changed it to initialize to mrc if (tls_emu || has_tls).
> Could this be a tristate instead? There are actually 3 cases:
>
> 1) We know the TLS reg is _always_ available i.e. ARMv6K, ARMV7 and
> above. In that case the test on elf_hwcap is redundant and wasteful.
>
> 2) We know the TLS reg is _never_ available i.e. pre-ARMv6. The test on
> elf_hwcap is again redundant and wasteful.
>
> 3) We're unsure as the actual CPU is known only at run time.
>
> Case #1 will become the common case in the future. Case #2 is still
> widely relevant for deployed systems in the field, and some popular
> ARMv5TE based SOCs are still produced right now. So instead of
> replacing #1 and #2 with #3, I think you should add #3 to the other
> cases instead.
OK. I've implemented this logic in new file tls.h.
> > #ifdef CONFIG_MMU
> > mcr p15, 0, r6, c3, c0, 0 @ Set domain register
> > @@ -1009,16 +1011,13 @@ kuser_cmpxchg_fixup:
> > */
> >
> > __kuser_get_tls: @ 0xffff0fe0
> > -
> > -#if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL)
> > - ldr r0, [pc, #(16 - 8)] @ TLS stored at 0xffff0ff0
> > -#else
> > - mrc p15, 0, r0, c13, c0, 3 @ read TLS register
> > -#endif
> > + nop @ read TLS, set in kuser_get_tls_init
> > usr_ret lr
> > -
> > - .rep 5
> > - .word 0 @ pad up to __kuser_helper_version
> > + mrc p15, 0, r0, c13, c0, 3 @ 0xffff0fe8 hardware TLS code
> > + ldr r0, [pc, #(16 - 8)] @ 0xffff0fec software TLS code
> > + .word 0 @ 0xffff0ff0 software TLS value
> > + nop @ pad up to __kuser_helper_version
> > + nop
> > .endr
>
> This looks obscur. The idea of patching the appropriate instruction at
> runtime here is a good one. However I'd simply keep the ldr version in
> place otherwise the pc displacement doesn't match anymore when
> disassembling. And simply overwrite it with the mrc version when
> necessary.
OK, changed to use the ldr by default.
> BTW you left a stray .endr here.
Oops. I've put back the .rep .endrep instead of the nops now.
> > + if ((((id >> 4) & 0xfff) == 0xb36) && (((id >> 20) & 3) == 0))
> > + elf_hwcap &= ~HWCAP_TLS;
>
> You should probably test for the vendor ID as well (ARM in this case).
OK, added.
> > +}
> > +#else
> > +static inline void feat_v6_fixup(void)
> > +{
> > +}
> > +#endif
>
> I think the #ifdef is unnecessary here. This is __init code anyway, so
> this could as well be always compiled in.
Removed.
> > diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> > index 1621e53..85dd001 100644
> > --- a/arch/arm/kernel/traps.c
> > +++ b/arch/arm/kernel/traps.c
> > @@ -518,16 +518,19 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
> >
> > case NR(set_tls):
> > thread->tp_value = regs->ARM_r0;
> > -#if defined(CONFIG_HAS_TLS_REG)
> > - asm ("mcr p15, 0, %0, c13, c0, 3" : : "r" (regs->ARM_r0) );
> > -#elif !defined(CONFIG_TLS_REG_EMUL)
> > - /*
> > - * User space must never try to access this directly.
> > - * Expect your app to break eventually if you do so.
> > - * The user helper at 0xffff0fe0 must be used instead.
> > - * (see entry-armv.S for details)
> > - */
> > - *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
> > +#if !defined(CONFIG_TLS_REG_EMUL)
> > + if (elf_hwcap & HWCAP_TLS) {
> > + asm ("mcr p15, 0, %0, c13, c0, 3"
> > + : : "r" (regs->ARM_r0));
> > + } else {
> > + /*
> > + * User space must never try to access this directly.
> > + * Expect your app to break eventually if you do so.
> > + * The user helper at 0xffff0fe0 must be used instead.
> > + * (see entry-armv.S for details)
> > + */
> > + *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
> > + }
> > #endif
>
> The same comment as for __kuser_get_tls would apply here. However,
> instead of duplicating the code block, you could define a macro, such as
> has_tls_reg(), that would be either 0, 1, or ((elf_hwcap & HWCAP_TLS).
Now using tls_emu and has_tls defines.
> > return 0;
> >
> > @@ -743,6 +746,21 @@ void __init trap_init(void)
> > return;
> > }
> >
> > +#if defined(CONFIG_TLS_REG_EMUL)
> > +static void __init kuser_get_tls_init(unsigned long vectors)
> > +{
> > + memcpy((void *)vectors + 0xfe0, (void *)vectors + 0xfe8, 4);
> > +}
> > +#else
> > +static void __init kuser_get_tls_init(unsigned long vectors)
> > +{
> > + if (elf_hwcap & HWCAP_TLS)
> > + memcpy((void *)vectors + 0xfe0, (void *)vectors + 0xfe8, 4);
> > + else
> > + memcpy((void *)vectors + 0xfe0, (void *)vectors + 0xfec, 4);
> > +}
> > +#endif
>
> Please move the #ifdef within the function body. Also it would be nice
> to add comments about what those magic offsets are.
This is now cleaner too with if (tls_emu || has_tls).
Updated patch below.
Regards,
Tony
commit 9747a3c92be523a73d338e2f26c0b645b200a0f4
Author: Tony Lindgren <tony@xxxxxxxxxxx>
Date: Tue Jun 29 13:34:53 2010 +0300
arm: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and check for it on V6
The TLS register is only available on ARM1136 r1p0 and later.
Set HWCAP_TLS flags if hardware TLS is available and test for
it if CONFIG_CPU_32v6K is not set for V6.
Note that we set the TLS instruction in __kuser_get_tls
dynamically as suggested by Jamie Lokier <jamie@xxxxxxxxxxxxx>.
Also the __switch_to code is optimized out in most cases as
suggested by Nicolas Pitre <nico@xxxxxxxxxxx>.
Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
diff --git a/arch/arm/include/asm/hwcap.h b/arch/arm/include/asm/hwcap.h
index f7bd52b..c1062c3 100644
--- a/arch/arm/include/asm/hwcap.h
+++ b/arch/arm/include/asm/hwcap.h
@@ -19,6 +19,7 @@
#define HWCAP_NEON 4096
#define HWCAP_VFPv3 8192
#define HWCAP_VFPv3D16 16384
+#define HWCAP_TLS 32768
#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
/*
diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h
new file mode 100644
index 0000000..5dcc71a
--- /dev/null
+++ b/arch/arm/include/asm/tls.h
@@ -0,0 +1,46 @@
+#ifndef __ASMARM_TLS_H
+#define __ASMARM_TLS_H
+
+#ifdef __ASSEMBLY__
+ .macro set_tls_none, tp, tmp1, tmp2
+ .endm
+
+ .macro set_tls_v6k, tp, tmp1, tmp2
+ mcr p15, 0, \tp, c13, c0, 3 @ set TLS register
+ .endm
+
+ .macro set_tls_v6, tp, tmp1, tmp2
+ ldr \tmp1, =elf_hwcap
+ ldr \tmp1, [\tmp1, #0]
+ mov \tmp2, #0xffff0fff
+ tst \tmp2, #HWCAP_TLS @ hardware TLS available?
+ mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register
+ streq \tp, [\tmp2, #-15] @ set TLS value at 0xffff0ff0
+ .endm
+
+ .macro set_tls_software, tp, tmp1, tmp2
+ mov \tmp1, #0xffff0fff
+ str \tp, [\tmp1, #-15] @ set TLS value at 0xffff0ff0
+ .endm
+#endif
+
+#ifdef CONFIG_TLS_REG_EMUL
+#define tls_emu 1
+#define has_tls 1
+#define set_tls set_tls_none
+#elif __LINUX_ARM_ARCH__ >= 7 || \
+ (__LINUX_ARM_ARCH__ == 6 && defined(CONFIG_CPU_32v6K))
+#define tls_emu 0
+#define has_tls 1
+#define set_tls set_tls_v6k
+#elif __LINUX_ARM_ARCH__ == 6
+#define tls_emu 0
+#define has_tls (elf_hwcap & HWCAP_TLS)
+#define set_tls set_tls_v6
+#else
+#define tls_emu 0
+#define has_tls 0
+#define set_tls set_tls_software
+#endif
+
+#endif /* __ASMARM_TLS_H */
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 7ee48e7..a6cfb17 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -22,6 +22,7 @@
#include <asm/thread_notify.h>
#include <asm/unwind.h>
#include <asm/unistd.h>
+#include <asm/tls.h>
#include "entry-header.S"
@@ -739,12 +740,7 @@ ENTRY(__switch_to)
#ifdef CONFIG_MMU
ldr r6, [r2, #TI_CPU_DOMAIN]
#endif
-#if defined(CONFIG_HAS_TLS_REG)
- mcr p15, 0, r3, c13, c0, 3 @ set TLS register
-#elif !defined(CONFIG_TLS_REG_EMUL)
- mov r4, #0xffff0fff
- str r3, [r4, #-15] @ TLS val at 0xffff0ff0
-#endif
+ set_tls r3, r4, r5
#ifdef CONFIG_MMU
mcr p15, 0, r6, c3, c0, 0 @ Set domain register
#endif
@@ -1009,17 +1005,12 @@ kuser_cmpxchg_fixup:
*/
__kuser_get_tls: @ 0xffff0fe0
-
-#if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL)
- ldr r0, [pc, #(16 - 8)] @ TLS stored at 0xffff0ff0
-#else
- mrc p15, 0, r0, c13, c0, 3 @ read TLS register
-#endif
+ ldr r0, [pc, #(16 - 8)] @ read TLS, set in kuser_get_tls_init
usr_ret lr
-
- .rep 5
- .word 0 @ pad up to __kuser_helper_version
- .endr
+ mrc p15, 0, r0, c13, c0, 3 @ 0xffff0fe8 hardware TLS code
+ .rep 4
+ .word 0 @ 0xffff0ff0 software TLS value, then
+ .endr @ pad up to __kuser_helper_version
/*
* Reference declaration:
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 122d999..de60733 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -269,6 +269,21 @@ static void __init cacheid_init(void)
extern struct proc_info_list *lookup_processor_type(unsigned int);
extern struct machine_desc *lookup_machine_type(unsigned int);
+static void __init feat_v6_fixup(void)
+{
+ int id = read_cpuid_id();
+
+ if (id & 0x410f0000 != 0x41070000)
+ return;
+
+ /*
+ * HWCAP_TLS is available only on 1136 r1p0 and later,
+ * see also kuser_get_tls_init.
+ */
+ if ((((id >> 4) & 0xfff) == 0xb36) && (((id >> 20) & 3) == 0))
+ elf_hwcap &= ~HWCAP_TLS;
+}
+
static void __init setup_processor(void)
{
struct proc_info_list *list;
@@ -311,6 +326,8 @@ static void __init setup_processor(void)
elf_hwcap &= ~HWCAP_THUMB;
#endif
+ feat_v6_fixup();
+
cacheid_init();
cpu_proc_init();
}
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 1621e53..e84d210 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -30,6 +30,7 @@
#include <asm/unistd.h>
#include <asm/traps.h>
#include <asm/unwind.h>
+#include <asm/tls.h>
#include "ptrace.h"
#include "signal.h"
@@ -518,17 +519,20 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
case NR(set_tls):
thread->tp_value = regs->ARM_r0;
-#if defined(CONFIG_HAS_TLS_REG)
- asm ("mcr p15, 0, %0, c13, c0, 3" : : "r" (regs->ARM_r0) );
-#elif !defined(CONFIG_TLS_REG_EMUL)
- /*
- * User space must never try to access this directly.
- * Expect your app to break eventually if you do so.
- * The user helper at 0xffff0fe0 must be used instead.
- * (see entry-armv.S for details)
- */
- *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
-#endif
+ if (tls_emu)
+ return 0;
+ if (has_tls) {
+ asm ("mcr p15, 0, %0, c13, c0, 3"
+ : : "r" (regs->ARM_r0));
+ } else {
+ /*
+ * User space must never try to access this directly.
+ * Expect your app to break eventually if you do so.
+ * The user helper at 0xffff0fe0 must be used instead.
+ * (see entry-armv.S for details)
+ */
+ *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
+ }
return 0;
#ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
@@ -743,6 +747,16 @@ void __init trap_init(void)
return;
}
+static void __init kuser_get_tls_init(unsigned long vectors)
+{
+ /*
+ * vectors + 0xfe0 = __kuser_get_tls
+ * vectors + 0xfe8 = hardware TLS instruction at 0xffff0fe8
+ */
+ if (tls_emu || has_tls)
+ memcpy((void *)vectors + 0xfe0, (void *)vectors + 0xfe8, 4);
+}
+
void __init early_trap_init(void)
{
unsigned long vectors = CONFIG_VECTORS_BASE;
@@ -761,6 +775,11 @@ void __init early_trap_init(void)
memcpy((void *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);
/*
+ * Do processor specific fixups for the kuser helpers
+ */
+ kuser_get_tls_init(vectors);
+
+ /*
* Copy signal return handlers into the vector page, and
* set sigreturn to be a pointer to these.
*/
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 346ae14..71d5d5e 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -717,17 +717,6 @@ config TLS_REG_EMUL
a few prototypes like that in existence) and therefore access to
that required register must be emulated.
-config HAS_TLS_REG
- bool
- depends on !TLS_REG_EMUL
- default y if SMP || CPU_32v7
- help
- This selects support for the CP15 thread register.
- It is defined to be available on some ARMv6 processors (including
- all SMP capable ARMv6's) or later processors. User space may
- assume directly accessing that register and always obtain the
- expected value only on ARMv7 and above.
-
config NEEDS_SYSCALL_FOR_CMPXCHG
bool
help
diff --git a/arch/arm/mm/proc-v6.S b/arch/arm/mm/proc-v6.S
index 7a5337e..e10626a 100644
--- a/arch/arm/mm/proc-v6.S
+++ b/arch/arm/mm/proc-v6.S
@@ -239,7 +239,8 @@ __v6_proc_info:
b __v6_setup
.long cpu_arch_name
.long cpu_elf_name
- .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_JAVA
+ /* See also feat_v6_fixup() for HWCAP_TLS */
+ .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_JAVA|HWCAP_TLS
.long cpu_v6_name
.long v6_processor_functions
.long v6wbi_tlb_fns
@@ -262,7 +263,8 @@ __pj4_v6_proc_info:
b __v6_setup
.long cpu_arch_name
.long cpu_elf_name
- .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP
+ /* See also feat_v6_fixup() for HWCAP_TLS */
+ .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS
.long cpu_pj4_name
.long v6_processor_functions
.long v6wbi_tlb_fns
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 7aaf88a..8071bcd 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -344,7 +344,7 @@ __v7_proc_info:
b __v7_setup
.long cpu_arch_name
.long cpu_elf_name
- .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP
+ .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS
.long cpu_v7_name
.long v7_processor_functions
.long v7wbi_tlb_fns
