[PATCH v2 18/22] tools/nolibc: add auxiliary vector retrieval for mips

Willy Tarreau
2023-01-10T07:26:22Z

In the _start block we now iterate over envp to find the auxiliary
vector after the NULL. The pointer is saved into an _auxv variable
that is marked as weak so that it's accessible from multiple units.

Signed-off-by: Willy Tarreau <w@1wt.eu>
---
tools/include/nolibc/arch-mips.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/tools/include/nolibc/arch-mips.h b/tools/include/nolibc/arch-mips.h
index 7d22f7bc38b3..bf83432d23ed 100644
--- a/tools/include/nolibc/arch-mips.h
+++ b/tools/include/nolibc/arch-mips.h
@@ -177,6 +177,7 @@ struct sys_stat_struct {
})

char **environ __attribute__((weak));
+const unsigned long *_auxv __attribute__((weak));

/* startup code, note that it's called __start on MIPS */
void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __start(void)
@@ -196,6 +197,16 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) __start(void)
"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
+
+ "move $t0, $a2\n" // iterate t0 over envp, look for NULL
+ "0:" // do {
+ "lw $a3, ($t0)\n" // a3=*(t0);
+ "bne $a3, $0, 0b\n" // } while (a3);
+ "addiu $t0, $t0, 4\n" // delayed slot: t0+=4;
+ "lui $a3, %hi(_auxv)\n" // load _auxv into a3 (hi)
+ "addiu $a3, %lo(_auxv)\n" // load _auxv into a3 (lo)
+ "sw $t0, ($a3)\n" // store t0 into _auxv
+
"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!
--
2.17.5