tools/nolibc: export environ as a weak symbol on mips

The environ is retrieved from the _start code and is easy to store at
this moment. Let's declare the variable weak and store the value into
it. By not being static it will be visible to all units. By being weak,
if some programs already declared it, they will continue to be able to
use it. This was tested with mips24kc (BE) both with environ inherited
from _start and extracted from envp.

Signed-off-by: Willy Tarreau <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>

Author: wtarreau

tools/include/nolibc/arch-mips.h

@@ -176,6 +176,8 @@ struct sys_stat_struct {
 	_arg4 ? -_num : _num;                                                 \
 })
 
+char **environ __attribute__((weak));
+
 /* startup code, note that it's called __start on MIPS */
 void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __start(void)
 {
@@ -191,6 +193,9 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __start(void)
 		"sll $a2, $a0, 2\n"     // a2 = argc * 4
 		"add   $a2, $a2, $a1\n" // envp = argv + 4*argc ...
 		"addiu $a2, $a2, 4\n"   //        ... + 4
+		"lui $a3, %hi(environ)\n"     // load environ into a3 (hi)
+		"addiu $a3, %lo(environ)\n"   // load environ into a3 (lo)
+		"sw $a2,($a3)\n"              // store envp(a2) into environ
 		"li $t0, -8\n"
 		"and $sp, $sp, $t0\n"   // sp must be 8-byte aligned
 		"addiu $sp,$sp,-16\n"   // the callee expects to save a0..a3 there!