[PATCH v2 17/22] tools/nolibc: add auxiliary vector retrieval for riscv

Willy Tarreau
2023-01-10T07:26:08Z

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.
It was tested on riscv64 only.

Signed-off-by: Willy Tarreau <w@1wt.eu>
---
tools/include/nolibc/arch-riscv.h | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/tools/include/nolibc/arch-riscv.h b/tools/include/nolibc/arch-riscv.h
index 1608e6bd94b9..e197fcb10ac0 100644
--- a/tools/include/nolibc/arch-riscv.h
+++ b/tools/include/nolibc/arch-riscv.h
@@ -171,6 +171,7 @@ struct sys_stat_struct {
})

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

/* startup code */
void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
@@ -185,6 +186,15 @@ void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
"slli a2, a0, "PTRLOG"\n" // envp (a2) = SZREG*argc ...
"add a2, a2, "SZREG"\n" // + SZREG (skip null)
"add a2,a2,a1\n" // + argv
+
+ "add a3, a2, zero\n" // iterate a3 over envp to find auxv (after NULL)
+ "0:\n" // do {
+ "ld a4, 0(a3)\n" // a4 = *a3;
+ "add a3, a3, "SZREG"\n" // a3 += sizeof(void*);
+ "bne a4, zero, 0b\n" // } while (a4);
+ "lui a4, %hi(_auxv)\n" // a4 = &_auxv (high bits)
+ "sd a3, %lo(_auxv)(a4)\n" // store a3 into _auxv
+
"lui a3, %hi(environ)\n" // a3 = &environ (high bits)
"sd a2,%lo(environ)(a3)\n" // store envp(a2) into environ
"andi sp,a1,-16\n" // sp must be 16-byte aligned
--
2.17.5