Commit f4738ff7 authored Mar 29, 2022 by Ammar Faizi Committed by Paul E. McKenney Apr 20, 2022

tools/nolibc: i386: Implement syscall with 6 arguments

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: x86@kernel.org
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/lkml/2e335ac54db44f1d8496583d97f9dab0@AcuMS.aculab.com


Suggested-by: David Laight <David.Laight@ACULAB.COM>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

parent 1590c598

tools/include/nolibc/arch-i386.h

+23 −0

Original line number	Diff line number	Diff line
		@@ -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: