On Tue, May 26, 2020 at 4:37 PM Russell King - ARM Linux admin
[off-list ref] wrote:

On Tue, May 26, 2020 at 04:32:49PM +0200, Linus Walleij wrote:

quoted

The act_mm assembly macro is actually partly reimplementing
get_thread_info so let's just use that.

Suggested-by: Russell King <linux@armlinux.org.uk>
Signed-off-by: Linus Walleij <redacted>
---
 arch/arm/mm/proc-macros.S | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index 60ac7c5999a9..65eaea85d3d6 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S

@@ -5,7 +5,6 @@
  *  VMA_VM_FLAGS
  *  VM_EXEC
  */
-#include <linux/const.h>
 #include <asm/asm-offsets.h>
 #include <asm/thread_info.h>

@@ -31,9 +30,7 @@
  * act_mm - get current->active_mm
  */
      .macro  act_mm, rd
-     bic     \rd, sp, #(THREAD_SIZE - 1) & ~63
-     bic     \rd, \rd, #63
-     ldr     \rd, [\rd, #TI_TASK]
+     get_thread_info \rd

This is not quite the same thing.

get_thread_info loads into \rd the address of the thread_info structure.
That's what the two bic instructions are doing.  The LDR is then loading
the address of the task_struct into \rd.

quoted

      .if (TSK_ACTIVE_MM > IMM12_MASK)
      add     \rd, \rd, #TSK_ACTIVE_MM & ~IMM12_MASK
      .endif

So this change alters which structure \rd is pointing to.

Oh I see it. I need to keep the last ldr     \rd, [\rd, #TI_TASK].

Strange that it wasn't crashing on me, I guess I was lucky.

I'll respin, thanks!

(The plan is to also make a patch to get_thread_info to use
bic like you pointed out, I'm just slow with my assembly.)

Yours,
Linus Walleij

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