Re: [RFC PATCH 3/4] powerpc: Optimize register usage for dear register

On Thu, Aug 5, 2021 at 6:09 PM Christophe Leroy
[off-list ref] wrote:

Le 26/07/2021 à 16:30, sxwjean@me.com a écrit :

quoted

From: Xiongwei Song <redacted>

Create an anonymous union for dar and dear regsiters, we can reference
dear to get the effective address when CONFIG_4xx=y or CONFIG_BOOKE=y.
Otherwise, reference dar. This makes code more clear.

Same comment here as for patch 1.

Same reply for the patch 1.
Thank you.

quoted

Signed-off-by: Xiongwei Song <redacted>
---
  arch/powerpc/include/asm/ptrace.h      | 5 ++++-
  arch/powerpc/include/uapi/asm/ptrace.h | 5 ++++-
  arch/powerpc/kernel/process.c          | 2 +-
  arch/powerpc/kernel/ptrace/ptrace.c    | 2 ++
  arch/powerpc/kernel/traps.c            | 5 ++++-
  arch/powerpc/mm/fault.c                | 2 +-
  6 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index c252d04b1206..fa725e3238c2 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h

@@ -43,7 +43,10 @@ struct pt_regs
                      unsigned long mq;
  #endif
                      unsigned long trap;
-                     unsigned long dar;
+                     union {
+                             unsigned long dar;
+                             unsigned long dear;
+                     };
                      union {
                              unsigned long dsisr;
                              unsigned long esr;

diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
index e357288b5f34..9ae150fb4c4b 100644
--- a/arch/powerpc/include/uapi/asm/ptrace.h
+++ b/arch/powerpc/include/uapi/asm/ptrace.h

@@ -52,7 +52,10 @@ struct pt_regs
      unsigned long trap;             /* Reason for being here */
      /* N.B. for critical exceptions on 4xx, the dar and dsisr
         fields are overloaded to hold srr0 and srr1. */
-     unsigned long dar;              /* Fault registers */
+     union {
+             unsigned long dar;              /* Fault registers */
+             unsigned long dear;
+     };
      union {
              unsigned long dsisr;            /* on Book-S used for DSISR */
              unsigned long esr;              /* on 4xx/Book-E used for ESR */

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index f74af8f9133c..50436b52c213 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c

@@ -1499,7 +1499,7 @@ static void __show_regs(struct pt_regs *regs)
          trap == INTERRUPT_DATA_STORAGE ||
          trap == INTERRUPT_ALIGNMENT) {
              if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
-                     pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, regs->esr);
+                     pr_cont("DEAR: "REG" ESR: "REG" ", regs->dear, regs->esr);
              else
                      pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);
      }

diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 00789ad2c4a3..969dca8b0718 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c

@@ -373,6 +373,8 @@ void __init pt_regs_check(void)
                   offsetof(struct user_pt_regs, trap));
      BUILD_BUG_ON(offsetof(struct pt_regs, dar) !=
                   offsetof(struct user_pt_regs, dar));
+     BUILD_BUG_ON(offsetof(struct pt_regs, dear) !=
+                  offsetof(struct user_pt_regs, dear));
      BUILD_BUG_ON(offsetof(struct pt_regs, dsisr) !=
                   offsetof(struct user_pt_regs, dsisr));
      BUILD_BUG_ON(offsetof(struct pt_regs, esr) !=

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 2164f5705a0b..0796630d3d23 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c

@@ -1609,7 +1609,10 @@ DEFINE_INTERRUPT_HANDLER(alignment_exception)
      }
  bad:
      if (user_mode(regs))
-             _exception(sig, regs, code, regs->dar);
+             if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
+                     _exception(sig, regs, code, regs->dear);
+             else
+                     _exception(sig, regs, code, regs->dar);
      else
              bad_page_fault(regs, sig);
  }

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 62953d4e7c93..3db6b39a1178 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c

@@ -542,7 +542,7 @@ static __always_inline void __do_page_fault(struct pt_regs *regs)
      long err;

      if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
-             err = ___do_page_fault(regs, regs->dar, regs->esr);
+             err = ___do_page_fault(regs, regs->dear, regs->esr);
      else
              err = ___do_page_fault(regs, regs->dar, regs->dsisr);