x86_64: Update THREAD_SETMEM/THREAD_SETMEM_NC for IMM64
Commit Message
Since there is only "movq imm32s, mem64" and no "movq imm64, mem64", use
"movq reg64, mem64" to store 64-bit constant in TCB.
---
sysdeps/x86_64/nptl/tls.h | 11 +++++++++++
1 file changed, 11 insertions(+)
Comments
On 2/2/21 2:12 PM, H.J. Lu via Libc-alpha wrote:
> Since there is only "movq imm32s, mem64" and no "movq imm64, mem64", use
> "movq reg64, mem64" to store 64-bit constant in TCB.
> ---
> sysdeps/x86_64/nptl/tls.h | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/sysdeps/x86_64/nptl/tls.h b/sysdeps/x86_64/nptl/tls.h
> index 20f0958780..9ec8703e45 100644
> --- a/sysdeps/x86_64/nptl/tls.h
> +++ b/sysdeps/x86_64/nptl/tls.h
> @@ -269,6 +269,11 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
> asm volatile ("movl %0,%%fs:%P1" : \
> : IMM_MODE (value), \
> "i" (offsetof (struct pthread, member))); \
> + else if (__builtin_constant_p (value) \
> + && (int64_t) (int32_t) (uintptr_t) value != (uintptr_t) value) \
> + asm volatile ("movq %0,%%fs:%P1" : \
> + : "r" (value), \
> + "i" (offsetof (struct pthread, member))); \
(1) Move conditional into 'else /* 8 */' section.
The blocks of conditionals are predicated on the size of the member we are
about to write to.
In the block below...
> else /* 8 */ \
... here, we are about to write value into a member that is size 8.
Your code changes the logical construction of the code, but in way that makes
it more difficult to understand.
We previously had:
if (sizeof() == 1)
else if (sizeof() == 4)
else /* Assume 8 */
In your case we must already be in the 'else /* Assume 8 */' because otherwise
we've be writing a 64-bit constant into a < 64-bit structure member.
I think we should put your code into the else clause.
272 else /* 8 */ \
273 { \
if (__builtin_constant_p (value)
&& ([the value is a >32-bit constant])
asm volatile ([use movq reg64, mem64]);
else
274 asm volatile ("movq %q0,%%fs:%P1" : \
275 : IMM_MODE ((uint64_t) cast_to_integer (value)), \
276 "i" (offsetof (struct pthread, member))); \
277 }})
(2) What if gcc can't prove it's constant?
If the constant is >32-bit, but gcc can't prove it's constant, then don't we
try to put a >32-bit constant into a 32-bit immediate?
Shouldn't the code be structured the other way around?
e.g.
else /* 8 */
{
if (__builtin_constant_p (value)
&& ([the value is a <= 32-bit constant])
asm volatile ([use movq imm32, mem64]);
else
asm volatile ([use movq reg64, mem64]);
}
This way the code is always correct?
> { \
> asm volatile ("movq %q0,%%fs:%P1" : \
> @@ -294,6 +299,12 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
> : IMM_MODE (value), \
> "i" (offsetof (struct pthread, member[0])), \
> "r" (idx)); \
> + else if (__builtin_constant_p (value) \
> + && (int64_t) (int32_t) (uintptr_t) value != (uintptr_t) value) \
> + asm volatile ("movq %0,%%fs:%P1(,%q2,8)" : \
> + : "r" (value), \
> + "i" (offsetof (struct pthread, member[0])), \
> + "r" (idx)); \
> else /* 8 */ \
> { \
> asm volatile ("movq %q0,%%fs:%P1(,%q2,8)" : \
>
@@ -269,6 +269,11 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
asm volatile ("movl %0,%%fs:%P1" : \
: IMM_MODE (value), \
"i" (offsetof (struct pthread, member))); \
+ else if (__builtin_constant_p (value) \
+ && (int64_t) (int32_t) (uintptr_t) value != (uintptr_t) value) \
+ asm volatile ("movq %0,%%fs:%P1" : \
+ : "r" (value), \
+ "i" (offsetof (struct pthread, member))); \
else /* 8 */ \
{ \
asm volatile ("movq %q0,%%fs:%P1" : \
@@ -294,6 +299,12 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
: IMM_MODE (value), \
"i" (offsetof (struct pthread, member[0])), \
"r" (idx)); \
+ else if (__builtin_constant_p (value) \
+ && (int64_t) (int32_t) (uintptr_t) value != (uintptr_t) value) \
+ asm volatile ("movq %0,%%fs:%P1(,%q2,8)" : \
+ : "r" (value), \
+ "i" (offsetof (struct pthread, member[0])), \
+ "r" (idx)); \
else /* 8 */ \
{ \
asm volatile ("movq %q0,%%fs:%P1(,%q2,8)" : \