linux-kernel - [PATCH 11/22] tools/nolibc: export environ as a weak symbol on riscv

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Date:   Mon,  9 Jan 2023 09:41:57 +0100
From:   Willy Tarreau <w@....eu>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Willy Tarreau <w@....eu>
Subject: [PATCH 11/22] tools/nolibc: export environ as a weak symbol on riscv

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 on riscv64 both with environ inherited from
_start and extracted from envp.

Signed-off-by: Willy Tarreau <w@....eu>
---
 tools/include/nolibc/arch-riscv.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/include/nolibc/arch-riscv.h b/tools/include/nolibc/arch-riscv.h
index c2b5db383d96..1608e6bd94b9 100644
--- a/tools/include/nolibc/arch-riscv.h
+++ b/tools/include/nolibc/arch-riscv.h
@@ -170,6 +170,8 @@ struct sys_stat_struct {
 	_arg1;                                                                \
 })

+char **environ __attribute__((weak));
+
 /* startup code */
 void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
 {
@@ -183,6 +185,8 @@ 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
+		"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
 		"call  main\n"               // main() returns the status code, we'll exit with it.
 		"li a7, 93\n"                // NR_exit == 93
-- 
2.17.5