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From:   Ammar Faizi <ammar.faizi@students.amikom.ac.id>
To:     Willy Tarreau <w@1wt.eu>
Cc:     Ammar Faizi <ammar.faizi@students.amikom.ac.id>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
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        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86-ml <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
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        Peter Cordes <peter@cordes.ca>,
        Bedirhan KURT <windowz414@gnuweeb.org>,
        Louvian Lyndal <louvianlyndal@gmail.com>
Subject: [PATCH 2/2] tools/nolibc: x86-64: Use `mov $60,%eax` instead of `mov $60,%rax`
Date:   Sun, 24 Oct 2021 09:11:32 +0700
Message-Id: <20211024015628.393550-2-ammarfaizi2@intel.com>
In-Reply-To: <20211024020616.395038-1-ammarfaizi2@intel.com>
References: <20211023134323.GA5881@1wt.eu>
 <20211024020616.395038-1-ammarfaizi2@intel.com>
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Note that mov to 32-bit register will zero extend to 64-bit register.
Thus `mov $60,%eax` has the same effect with `mov $60,%rax`. Use the
shorter opcode to achieve the same thing.
```
  b8 3c 00 00 00       	mov    $60,%eax (5 bytes) [1]
  48 c7 c0 3c 00 00 00 	mov    $60,%rax (7 bytes) [2]
```
Currently, we use [2]. Change it to [1] for shorter code.

Signed-off-by: Ammar Faizi <ammar.faizi@students.amikom.ac.id>
---
 tools/include/nolibc/nolibc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h
index ea38d6f356a1..b1a81f711327 100644
--- a/tools/include/nolibc/nolibc.h
+++ b/tools/include/nolibc/nolibc.h
@@ -420,7 +420,7 @@ asm(".section .text\n"
     "and $-16, %rsp\n"          // x86 ABI : esp must be 16-byte aligned before call
     "call main\n"               // main() returns the status code, we'll exit with it.
     "movzb %al, %rdi\n"         // retrieve exit code from 8 lower bits
-    "mov $60, %rax\n"           // NR_exit == 60
+    "mov $60, %eax\n"           // NR_exit == 60
     "syscall\n"                 // really exit
     "hlt\n"                     // ensure it does not return
     "");
-- 
2.30.2