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>

diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h
index 10aada40680dfdcec4483efa70e236a054e22f74..d7e7212346e2fb9a4e7a709948891023f5a7aa2b 100644 (file)
--- 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: