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From: Ammar Faizi <[email protected]>
To: Willy Tarreau <[email protected]>
Cc: Ammar Faizi <[email protected]>,
	Alviro Iskandar Setiawan <[email protected]>,
	Nugraha <[email protected]>,
	"Paul E. McKenney" <[email protected]>,
	Linux Kernel Mailing List <[email protected]>,
	GNU/Weeb Mailing List <[email protected]>,
	[email protected], [email protected],
	David Laight <[email protected]>
Subject: [PATCH v2 4/9] tools/nolibc: i386: Implement syscall with 6 arguments
Date: Tue, 29 Mar 2022 17:17:32 +0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On i386, the 6th argument of syscall goes in %ebp. However, both Clang
and GCC cannot use %ebp in the clobber list and in the "r" constraint
without using -fomit-frame-pointer. To make it always available for
any kind of compilation, the below workaround is implemented.

  1) Push the 6-th argument.
  2) Push %ebp.
  3) Load the 6-th argument from 4(%esp) to %ebp.
  4) Do the syscall (int $0x80).
  5) Pop %ebp (restore the old value of %ebp).
  6) Add %esp by 4 (undo the stack pointer).

Cc: [email protected]
Cc: [email protected]
Link: https://lore.kernel.org/lkml/[email protected]
Suggested-by: David Laight <[email protected]>
Signed-off-by: Ammar Faizi <[email protected]>
===
@@ Changelog:

   Link v1: https://lore.gnuweeb.org/gwml/[email protected]
   v1 -> v2:
    * No changes *

   Link RFC v2: https://lore.kernel.org/lkml/[email protected]
   RFC v2 -> v1:
    - Use the same pattern for syscall6, regardless using GCC or Clang
      (comment from David).
    - Use appropriate constraints for syscall6 instead of always using
      register variables (comment from David).

   Link RFC v1: https://lore.kernel.org/llvm/[email protected]
   RFC v1 -> RFC v2:
    - Fix %ebp saving method. Don't use redzone, i386 doesn't have a redzone
      (comment from David and Alviro).
---
 tools/include/nolibc/arch-i386.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h
index 10aada40680d..d7e7212346e2 100644
--- a/tools/include/nolibc/arch-i386.h
+++ b/tools/include/nolibc/arch-i386.h
@@ -167,6 +167,29 @@ struct sys_stat_struct {
 	_ret;                                                                 \
 })
 
+#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6)	\
+({								\
+	long _eax  = (long)(num);				\
+	long _arg6 = (long)(arg6); /* Always in memory */	\
+	__asm__ volatile (					\
+		"pushl	%[_arg6]\n\t"				\
+		"pushl	%%ebp\n\t"				\
+		"movl	4(%%esp),%%ebp\n\t"			\
+		"int	$0x80\n\t"				\
+		"popl	%%ebp\n\t"				\
+		"addl	$4,%%esp\n\t"				\
+		: "+a"(_eax)		/* %eax */		\
+		: "b"(arg1),		/* %ebx */		\
+		  "c"(arg2),		/* %ecx */		\
+		  "d"(arg3),		/* %edx */		\
+		  "S"(arg4),		/* %esi */		\
+		  "D"(arg5),		/* %edi */		\
+		  [_arg6]"m"(_arg6)	/* memory */		\
+		: "memory", "cc"				\
+	);							\
+	_eax;							\
+})
+
 /* startup code */
 /*
  * i386 System V ABI mandates:
-- 
Ammar Faizi


  parent reply	other threads:[~2022-03-29 10:17 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-29 10:17 [PATCH v2 0/9] Add dynamic memory allocator support for nolibc Ammar Faizi
2022-03-29 10:17 ` [PATCH v2 1/9] tools/nolibc: x86-64: Update System V ABI document link Ammar Faizi
2022-03-29 10:17 ` [PATCH v2 2/9] tools/nolibc: Replace `asm` with `__asm__` Ammar Faizi
2022-03-29 10:17 ` [PATCH v2 3/9] tools/nolibc: Remove .global _start from the entry point code Ammar Faizi
2022-03-29 10:17 ` Ammar Faizi [this message]
2022-03-29 10:17 ` [PATCH v2 5/9] tools/nolibc/sys: Implement `mmap()` and `munmap()` Ammar Faizi
2022-03-29 10:17 ` [PATCH v2 6/9] tools/nolibc/types: Implement `offsetof()` and `container_of()` macro Ammar Faizi
2022-03-29 10:17 ` [PATCH v2 7/9] tools/nolibc/stdlib: Implement `malloc()`, `calloc()`, `realloc()` and `free()` Ammar Faizi
2022-03-29 10:17 ` [PATCH v2 8/9] tools/nolibc/string: Implement `strnlen()` Ammar Faizi
2022-03-29 10:17 ` [PATCH v2 9/9] tools/include/string: Implement `strdup()` and `strndup()` Ammar Faizi
2022-03-29 10:20 ` [PATCH v2 0/9] Add dynamic memory allocator support for nolibc Ammar Faizi
2022-03-30  2:41   ` Willy Tarreau
2022-03-30 18:51     ` Paul E. McKenney
2022-03-31  6:34       ` Willy Tarreau

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