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tools/nolibc: i386: Implement syscall with 6 arguments

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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>
This commit is contained in:
Ammar Faizi 2022-03-29 17:17:32 +07:00 committed by Paul E. McKenney
parent 1590c59836
commit f4738ff74c
1 changed files with 23 additions and 0 deletions
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23
tools/include/nolibc/arch-i386.h
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@ -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: